Object default value
Is it possible to have a default value associated python objects? I.e. to flag an attribute in such a way that the assignment operator for the object returns the default attribute instead of the object itself, but calls to other object attributes are properly resolved? (I don't think so, but I am not sure) Example: class obj(object): x=1 #assume x is somehow made into a default value y=2 Ideally this should be the result: myobj=obj() print myobj #-> 1 print myobj.y #-> 2 x=myobj print x #-> 1 print type(x) #int Those are my half-working solutions so far: 1) using __get__ descriptor within the class, def __get__(self,parent,parenttype): return self.x then print myobj #works print myobj.y #does not work! equivalent to: print 1.y 2) Use a __call__ method without a __get__ descriptor. def __call__(self): return self.x then: print myobj() #works, but not the same as: print myobj print myobj.y #works -- http://mail.python.org/mailman/listinfo/python-list
Re: Object default value
The prints can be done by defining an __str__ method on the class, but I don't think you will get the type(obj) to work the way you want. class obj(object): __default=1 y=2 def __str__(self): return str(self.__default) myobj=obj() print "myobj=", myobj print "myobj.y=", myobj.y >>> myobj= 1 >>> myobj.y= 2 ago wrote: > Is it possible to have a default value associated python objects? I.e. > to flag an attribute in such a way that the assignment operator for the > object returns the default attribute instead of the object itself, but > calls to other object attributes are properly resolved? (I don't think > so, but I am not sure) > > Example: > > class obj(object): > x=1 #assume x is somehow made into a default value > y=2 > > Ideally this should be the result: > > myobj=obj() > print myobj #-> 1 > print myobj.y #-> 2 > x=myobj > print x #-> 1 > print type(x) #int > > Those are my half-working solutions so far: > > 1) using __get__ descriptor within the class, > > def __get__(self,parent,parenttype): return self.x > > then > > print myobj #works > print myobj.y #does not work! equivalent to: print 1.y > > 2) Use a __call__ method without a __get__ descriptor. > > def __call__(self): return self.x > > then: > > print myobj() #works, but not the same as: print myobj > print myobj.y #works > -- http://mail.python.org/mailman/listinfo/python-list
Re: Object default value
The print statement was only for illustrative purposes, when calling varx=myobj I need to receive obj.x as opposed to the instance of obj, but I also need to call vary=myobj.y. Something like that exists for com objects/VB, for instance an excel range object uses value as the default attribute, so that you can write set rng=range(...); x=rng y=rng.value 'x==y z=rng.attributeXYZ -- http://mail.python.org/mailman/listinfo/python-list
Re: Object default value
I think you want to overload the assignment operator here. I'm not sure that is allowed in python (I've never seen it done). You can overload the equality, lt, gt, le, ge operators (==, <, ...) such that class Thing: x = 5 def __str__(self): return str(self.x) def __eq__(self, other): if hasattr(other, 'x'): return self.x == other.x else: return self.x == other py> athing = Thing() py> athing.x 5 py> bob = athing.x py> athing == bob # having overlaoded equality for athing True py> athing is bob # not the same object False But I don't think assignment overloading is allowed in python: py> athing = Thing() py> print athing # having overloaded __str__() 5 py> bob = athing py> type(bob) # will not be an int ==> python language constraint James On Tuesday 20 September 2005 13:05, ago wrote: > The print statement was only for illustrative purposes, when calling > varx=myobj I need to receive obj.x as opposed to the instance of obj, > but I also need to call vary=myobj.y. Something like that exists for > com objects/VB, for instance an excel range object uses value as the > default attribute, so that you can write > > set rng=range(...); > x=rng > y=rng.value > 'x==y > z=rng.attributeXYZ -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com/ -- http://mail.python.org/mailman/listinfo/python-list
Re: Object default value
See this recent clpy thread: http://www.thescripts.com/forum/thread19253.html On Tuesday 20 September 2005 13:05, ago wrote: > The print statement was only for illustrative purposes, when calling > varx=myobj I need to receive obj.x as opposed to the instance of obj, > but I also need to call vary=myobj.y. Something like that exists for > com objects/VB, for instance an excel range object uses value as the > default attribute, so that you can write > > set rng=range(...); > x=rng > y=rng.value > 'x==y > z=rng.attributeXYZ -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com/ -- http://mail.python.org/mailman/listinfo/python-list
Re: Object default value
> I think you want to overload the assignment operator here. I'm not sure that > is allowed in python (I've never seen it done). You can't because assignment is not an operator in Python. Is it safe to assume that the OP's next question will be how to invoke functions without the ()'s? To save you the trouble, then answer is 'no'. Python is simple, VB is simple, but Python is not VB. -- Paul -- http://mail.python.org/mailman/listinfo/python-list
Re: Object default value
ago wrote: > Is it possible to have a default value associated python objects? I.e. > to flag an attribute in such a way that the assignment operator for the > object returns the default attribute instead of the object itself, but > calls to other object attributes are properly resolved? (I don't think > so, but I am not sure) You're descriptions aren't very clear. Maybe you can put that in a greater context - what do you want to achieve? And the assignment-operator isn't overloadable - that is for sure! Diez -- http://mail.python.org/mailman/listinfo/python-list
Re: Object default value
I am trying to write a generic DataAttribute class in order to simplify access to object attributes and attached attribute-metadata for end users with little programming experience. Requirement 1: accessing the "default" value should be easy (using assignment operator, via descriptors like __get__ and __set__). Requirement 2: access to the attribute-metadata should also be as intuitive as possible. Requirement 3: possibly the DataAttribute should also be callable, to return for instance, an history of its values. class DataAttribute(object): value=1 #default old=2 class Obj(object): attr=DataAttribute() #From end user prospective, ideally: obj=Obj() x = obj.attr #x=1 xold = obj.attr.old #xold=2 obj.attr = 3 #obj.attr.value=3 xold = obj.attr.old #xold=1 xhistory = obj.attr(startdate, enddate) #xhistory = [[date1, 4],[date2,5],[date3,6]] xtimestmap = x.attr.timestamp print obj.attr == obj.attr.value #True If I use __get__ then I cannot access the metadata. I could create a separate Obj attribute for each metadata item, but then I would litter the Obj namespace (typical object will have several attributes each with lots of metadata) and potentially create name conflicts. Not to mention that DataAttributes should be attached/deleted on the fly and if each attribute becames a set of attributes this operation is complex (metclasses?). If I use __call__ + __set__ but then I am introducing an asymmetry: x = obj.attr() obj.attr = 2 I could use getters and setters but that is not really convenient nor intuitive -- http://mail.python.org/mailman/listinfo/python-list
Re: Object default value
> Is it safe to assume that the OP's next question will be how to invoke functions without the ()'s? To save you the trouble, then answer is 'no'. You probably nailed it, thanks for the answer. I suspected that was the case. I think I'll use __call__ + __set__ -- http://mail.python.org/mailman/listinfo/python-list
Re: Object default value
In fact even IF I could get a default value to work as mentioned, then I would be creating potential name conflicts between the DataAttribute.DefaultValue and the other metadata. I.e. when calling obj.attr.x I could refer to DataAttribute.x or DataAttribute.value.x. It's a no go. -- http://mail.python.org/mailman/listinfo/python-list
Re: Object default value
James Stroud wrote: > I think you want to overload the assignment operator here. I'm not sure that > is allowed in python (I've never seen it done) > But I don't think assignment overloading is allowed in python: Exactly correct. Assignment is an operation on a namespace using a new value, and does not involve the former value. Something similar to assignment overloading is possible with properties, but you need to be using object attributes, not names in a module (or function locals). class SomeDemo(object): def _read_foo(self): print 'Reading foo' return self._foo def _write_foo(self, value): print 'Writing foo as %r' % value return self._foo def _del_foo(self): print 'Deleting foo' del self._foo foo = property(_read_foo, _write_foo, _del_foo) obj = SomeDemo() obj.foo = 123 obj.foo += 1 del obj.foo --Scott David Daniels [EMAIL PROTECTED] -- http://mail.python.org/mailman/listinfo/python-list
Re: Object default value
"ago" <[EMAIL PROTECTED]> wrote: > Is it possible to have a default value associated python objects? I.e. > to flag an attribute in such a way that the assignment operator for the > object returns the default attribute instead of the object itself, but > calls to other object attributes are properly resolved? (I don't think > so, but I am not sure) No. You can overload certain methods to make an object behave like one of its attributes in certain contexts (e.g. comparisions, math operations, conversions), but you cannot do it for all operations. Especially not the "assignment operator", since there is no such thing in Python. (assignment is a statement, and it's an operation on the target namespace, not the source object). (As always, Python works better if you use it to write Python programs) -- http://mail.python.org/mailman/listinfo/python-list
Re: Object default value
On Tuesday 20 September 2005 12:31, ago wrote: > Is it possible to have a default value associated python objects? I.e. > to flag an attribute in such a way that the assignment operator for the > object returns the default attribute instead of the object itself, but > calls to other object attributes are properly resolved? (I don't think > so, but I am not sure) I was thinking about this last night and it seemed an interesting problem. I thought you might want to change the way you look at it, using the python equivalent to type casting (maybe its called "coercing", sorry for my poor command of python vocabulary). I have overridden __int__ and __float__ for this example. You might want to look into __coerce__. This should have the behavior you desire while having the explicit syntax expected of good python code. Inheriting from list allows you to use a stack-like behavior you described in a previous email. You can further modify __getattribute__, __setattribute__, __delattribute__, etc. Overriding __iter__ gives you the history in "correct" order, but may begin to embark on a non-intuitive interface--you be the judge. I think this is about as close as you can get in python to what you are thinking (don't know the oldest python version this is backwards compatible with): py> class Thing(list): ...def __init__(self, start_value): ... list.__init__(self) ... self.append(start_value) ...def __setattr__(self, anattr, aval): ... if (anattr == 'top'): ...self.append(aval) ... else: ...list.__setattr__(self, anattr, aval) ...def __getattr__(self, anattr): ... if (anattr == 'top'): ...return self[-1] ... elif (anattr == 'old'): ...try: ... return self[-2] ...except IndexError: ... raise NameError, "No old value yet" ... else: ...list.__getattr__(self, anattr) ...def __iter__(self): ... return list.__iter__(self[::-1]) ...def __int__(self): ... return int(self.top) ...def __float__(self): ... return float(self.top) ...def __str__(self): ... return str(self.top) ... py> athing = Thing(5)# should init with a reasonable value py> athing.top # __getattr__ 5 py> int(athing) # __int__ 5 py> print athing # __str__ 5 py> float(athing)# __float__ 5.0 py> athing.top = 4 # __setattr__ py> print athing 4 py> athing.old # __getattr__ 5 py> athing.top = 42 # __setattr__ py> [x for x in athing] # __iter__ [42, 4, 5] py> y = float(athing)# closest you can get to assignment overloading py> print y # y is a float 42.0 py> athing # Thing inherits from list, so you get list.__repr__() here [5, 4, 42] Here it is without the prompts: class Thing(list): def __init__(self, start_value): list.__init__(self) self.append(start_value) def __setattr__(self, anattr, aval): if (anattr == 'top'): self.append(aval) else: list.__setattr__(self, anattr, aval) def __getattr__(self, anattr): if (anattr == 'top'): return self[-1] elif (anattr == 'old'): try: return self[-2] except IndexError: raise NameError, "No old value yet" else: list.__getattr__(self, anattr) def __iter__(self): return list.__iter__(self[::-1]) def __int__(self): return int(self.top) def __float__(self): return float(self.top) def __str__(self): return str(self.top) -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com/ -- http://mail.python.org/mailman/listinfo/python-list
Re: Object default value
On 20 Sep 2005 12:31:19 -0700, "ago" <[EMAIL PROTECTED]> wrote: >Is it possible to have a default value associated python objects? I.e. >to flag an attribute in such a way that the assignment operator for the >object returns the default attribute instead of the object itself, but >calls to other object attributes are properly resolved? (I don't think >so, but I am not sure) > >Example: > >class obj(object): > x=1 #assume x is somehow made into a default value > y=2 > >Ideally this should be the result: > >myobj=obj() normal >print myobj #-> 1 expression myobj interpreted as myobj.x? >print myobj.y #-> 2 normal >x=myobj normal, because expression myobj in this context of immediate assignment does not mean myobj.x? >print x #-> 1 expression x is the same as expression myobj, which is intrpreted as myobj.x (alias x.x) if not assigned? >print type(x) #int ditto > If you wanted to have this effect inside a function, you could write a byte-code-munging decorator to evaluate selected_name as selected_name.selected_attr except where assigning to an alias name is all that a statement does, as in x = myobj. But what if you actually wanted to pass the object per se somewhere, or return it from a function? Maybe you could have the expression myobj.x mean the normal myobj, and vice versa in a kind of terrible symmetry ;-) Then usage might be something like @agostino_effect(myobj='x') # eval myobj as myobj.x def foo(): myobj=obj() print myobj #-> 1 print myobj.y #-> 2 x = myobj print x #-> 1 return x, myobj, x.y, myobj.x # with .x having "symmetrically-other" effect ;-) xval, myobjval, x_dot_y_val, myobj_per_se = foo() # assignment from function is not interfered with myobj_per_se.y #->2 myobj_per_se #-> 1 myobj_val.y -> AttributeError: 'int' object has no attribute 'y' I'm not suggesting this is a good way to go forward, I am just playing with the feasibility of doing what you want, even if it's not good for you ;-) I suspect there is a better way, but it wouldn't be that hard to do the above, as you can see from the code of foo that the agostino_effect decorator would be modifying: >>> def foo(): ... myobj=obj() ... print myobj #-> 1 ... print myobj.y #-> 2 ... x = myobj ... print x #-> 1 ... return x, myobj, x.y, myobj.x # with .x having "symmetrically-other" effect ;-) ... >>> import dis >>> dis.dis(foo) 2 0 LOAD_GLOBAL 0 (obj) 3 CALL_FUNCTION0 6 STORE_FAST 0 (myobj) 3 9 LOAD_FAST0 (myobj) Here you'd notice that the next instruction was not STORE_FAST so you'd insert a LOAD_ATTR1 (x) similar to the .y access below 12 PRINT_ITEM 13 PRINT_NEWLINE 4 14 LOAD_FAST0 (myobj) 17 LOAD_ATTR2 (y) Here you'd notice the above wasn't LOAD_ATTR (x) (which you'd otherwise have to remove for object-per-se) 20 PRINT_ITEM 21 PRINT_NEWLINE 5 22 LOAD_FAST0 (myobj) 25 STORE_FAST 1 (x) This you notice is an immediate assignment and you leave it alone, and note the alias 6 28 LOAD_FAST1 (x) Here you notice the alias and insert LOAD_ATTR1 (x) as before with myobj 31 PRINT_ITEM 32 PRINT_NEWLINE 7 33 LOAD_FAST1 (x) insert LOAD_ATTR1 (x) again 36 LOAD_FAST0 (myobj) insert LOAD_ATTR1 (x) again 39 LOAD_FAST1 (x) 42 LOAD_ATTR2 (y) other attribute, no change to above byte code 45 LOAD_FAST0 (myobj) 48 LOAD_ATTR3 (x) anti-attribute, remove above byte code 51 BUILD_TUPLE 4 54 RETURN_VALUE You might want to do the same for LOAD_GLOBAL/STORE_GLOBAL, and STORE_DEREF/LOAD_DEREF, I don't know. But it wouldn't be a big deal to get a hack working. Thorough testing is another matter, not to mention justifying it ;-) Regards, Bengt Richter -- http://mail.python.org/mailman/listinfo/python-list
Re: Object default value
ago wrote: > Is it possible to have a default value associated python objects? I.e. > to flag an attribute in such a way that the assignment operator for the > object returns the default attribute instead of the object itself, but > calls to other object attributes are properly resolved? (I don't think > so, but I am not sure) Python is not Visual Basic. In Visual Basic, objects could have a default property which was set when the object variable was assigned to, but that was only possible because object variables had to be set with "Set", not "Let". Reinhold -- http://mail.python.org/mailman/listinfo/python-list
default value in a list
Hi,
Is there an elegant way to assign to a list from a list of unknown
size? For example, how could you do something like:
>>> a, b, c = (line.split(':'))
if line could have less than three fields?
Thanks,
TB
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Default value for Listbox (Tkinter)
Whenever I set up something similar: vals = ['1', '2','3'] for v in vals: listbox.inset(END, v) I notice that when this listbox is displayed, there is never a default value. How can I make sure that one of the indices is selected by default? Thanks, Harlin -- http://mail.python.org/mailman/listinfo/python-list
default value for list access?
Dear list,
My program needs to do calculation based on a giving data structure
(like a sparse matrix) with lots of missing values (invalid
indices/keys of lists/dictionaries).
The programing is difficult in that I have to use a try...except block
for every item access. I have written a function
def getItem(item, idx, default):
try:
return item[idx]
except:
return default
Then I will have to write a[1]['a'][4] as
getItem( getItem( getItem(a,1,{}), 'a', []), 4, 0)
Is there any way to automatically return 0 when any exception is raised
for such data acceses? (automatic wrapping a[...] as
try:
a[...]
except:
0
)
Many thanks in advance.
Bo
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Providing 'default' value with raw_input()?
Hi All, As always, my posts come with a 'Warning: Newbie lies ahead!' disclaimer... I'm wondering if it's possible, using raw_input(), to provide a 'default' value with the prompt? I would like to include the ability to edit an existing value (drawn from an SQLite table) using a DOS console Python app, but my gut feeling from reading what I can find about raw_input() is that it only allows you to provide a prompt, not a default value as well. If anyone can give me any advice on how I might achieve this, I would be immensely appreciative! Many thanks and much warmth, planetthoughtful -- http://mail.python.org/mailman/listinfo/python-list
Re: default value in a list
What do you want put into the "missing" variables?
I'll assume None. Something like following
works:
values=line.split(':')
try: a=values.pop(0)
except IndexError: a=None
try: b=values.pop(0)
except IndexError: b=None
try: c=values.pop(0)
except IndexError: c=None
Larry Bates
TB wrote:
Hi,
Is there an elegant way to assign to a list from a list of unknown
size? For example, how could you do something like:
a, b, c = (line.split(':'))
if line could have less than three fields?
Thanks,
TB
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Re: default value in a list
TB wrote:
Hi,
Is there an elegant way to assign to a list from a list of unknown
size? For example, how could you do something like:
a, b, c = (line.split(':'))
if line could have less than three fields?
l = line.split(':')
l is a list, whose length will be one more than the number of colons in
the line.
You can access the elements of the list using a[0], a[2], and so on. For
example:
>>> line = "This:is:a:sample:line"
>>> l = line.split(':')
>>> l
['This', 'is', 'a', 'sample', 'line']
>>> for w in l:
... print w
...
This
is
a
sample
line
>>> len(l)
5
>>>
regards
Steve
--
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Python Web Programming http://pydish.holdenweb.com/
Holden Web LLC +1 703 861 4237 +1 800 494 3119
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Re: default value in a list
"TB" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> Hi,
>
> Is there an elegant way to assign to a list from a list of unknown
> size? For example, how could you do something like:
>
> >>> a, b, c = (line.split(':'))
> if line could have less than three fields?
>
> Thanks,
> TB
>
I asked a very similar question a few weeks ago, and from the various
suggestions, I came up with this:
line = ":BBB"
expand = lambda lst,default,minlen : (lst + [default]*minlen)[0:minlen]
a,b,c = expand( line.split(":"), "", 3 )
print a
print b
print c
-- Paul
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Re: default value in a list
Paul McGuire wrote: expand = lambda lst,default,minlen : (lst + [default]*minlen)[0:minlen] Or if you're afraid of lambda like me: def expand(lst,default,minlen):return (lst + [default]*minlen)[0:minlen] or perhaps more readably: def expand(lst, default, minlen): return (lst + [default]*minlen)[0:minlen] No need for an anonymous function when you're naming it. ;) Steve -- http://mail.python.org/mailman/listinfo/python-list
Re: default value in a list
TB wrote:
Hi,
Is there an elegant way to assign to a list from a list of unknown
size? For example, how could you do something like:
a, b, c = (line.split(':'))
if line could have less than three fields?
(Note that you're actually assigning to a group of local variables,
via tuple unpacking, not assigning to a list...)
One could also do something like this:
>>> l = "a:b:c".split(':')
>>> a, b, c, d, e = l + ([None] * (5 - len(l)))
>>> print (a, b, c, d, e)
('a', 'b', 'c', None, None)
>>>
Personally, though, I can't help but think that, if you're not certain
how many fields are in a string, then splitting it into independent
variables (rather than, say, a list or dict) *cannot* be an elegant
solution. If the fields deserve independent names, then they must
have a definite (and distinct) meaning; if they have a distinct
meaning (as opposed to being a series of similar items, in which case
you should keep them in a list), then which field is it that's
missing? Are you sure it's *always* the last fields? This feels to
me like the wrong solution to any problem.
Hm, speaking of fields makes me think of classes.
>>> class LineObj:
... def __init__(self, a=None, b=None, c=None, d=None, e=None):
... self.a = a
... self.b = b
... self.c = c
... self.d = d
... self.e = e
...
>>> l = "a:b:c".split(':')
>>> o = LineObj(*l)
>>> o.__dict__
{'a': 'a', 'c': 'c', 'b': 'b', 'e': None, 'd': None}
>>>
This is a bit more likely to be meaningful, in that there's almost
certainly some logical connection between the fields of the line
you're splitting and keeping them as a class demonstrates that
connection, but it still seems a bit smelly to me.
Jeff Shannon
Technician/Programmer
Credit International
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Re: default value in a list
Paul McGuire wrote: > I asked a very similar question a few weeks ago, and from the various > suggestions, I came up with this: > > expand = lambda lst,default,minlen : (lst + [default]*minlen)[0:minlen] I wouldn't trust whoever suggested that. if you want a function, use a function: def expand(seq, default, minlen): return (seq + [default]*minlen)[:minlen] -- http://mail.python.org/mailman/listinfo/python-list
Re: default value in a list
TB <[EMAIL PROTECTED]> wrote:
> Is there an elegant way to assign to a list from a list of unknown
> size? For example, how could you do something like:
>
> >>> a, b, c = (line.split(':'))
> if line could have less than three fields?
import itertools as it
a, b, c = it.islice(
it.chain(
line.split(':'),
it.repeat(some_default),
),
3)
I find itertools-based solutions to be generally quite elegant.
This one assumes you want to assign some_default to variables in the LHS
target beyond the length of the RHS list. If what you want is to repeat
the RHS list over and over instead, this simplifies the first argument
of islice:
a, b, c = it.islice(it.cycle(line.split(':')), 3)
Of course, you can always choose to write your own generator instead of
building it up with itertools. itertools solutions tend to be faster,
and I think it's good to get familiar with that precious modules, but
without such familiarity many readers may find a specially coded
generator easier to follow. E.g.:
def pad_with_default(N, iterable, default=None):
it = iter(iterable)
for x in it:
if N<=0: break
yield x
N -= 1
while N>0:
yield default
N -= 1
a, b, c = pad_with_default(3, line.split(':'))
The itertools-based solution hinges on a higher level of abstraction,
glueing and tweaking iterators as "atoms"; the innards of a custom coded
generator tend to be programmed at a lower level of abstraction,
reasoning in item-by-item mode. There are pluses and minuses to each
approach; I think in the long range higher abstraction pays off, so it's
worth the investment to train yourself to use itertools.
In the Python Cookbook new 2nd edition, due out in a couple months,
we've added a whole new chapter about iterators and generators, since
it's such a major subfield in today's Python (as evidenced by the wealth
of recipes submitted to Activestate's online cookbook sites on the
subject). A couple of recipes have do with multiple unpacking
assignment -- one of them, in particular, is an evil hack which peers
into the caller's bytecode to find out how many items are on the LHS, so
you don't have to pass that '3' explicitly. I guess that might be
considered "elegant", for suitably contorted meanings of "elegant"...
it's on the site, too, but I don't have the URL at hand. It's
instructive, anyway, but I wouldn't suggest actually using it in any
kind of production code...
Alex
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Re: default value in a list
Paul McGuire wrote:
>> Is there an elegant way to assign to a list from a list of unknown
>> size? For example, how could you do something like:
>>
>> >>> a, b, c = (line.split(':'))
>> if line could have less than three fields?
> I asked a very similar question a few weeks ago, and from the various
> suggestions, I came up with this:
>
> line = ":BBB"
> expand = lambda lst,default,minlen : (lst + [default]*minlen)[0:minlen]
> a,b,c = expand( line.split(":"), "", 3 )
Here is an expand() variant that is not restricted to lists but works with
arbitrary iterables:
from itertools import chain, repeat, islice
def expand(iterable, length, default=None):
return islice(chain(iterable, repeat(default)), length)
Peter
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Re: default value in a list
Peter Otten wrote:
> Paul McGuire wrote:
>
>>> Is there an elegant way to assign to a list from a list of unknown
>>> size? For example, how could you do something like:
>>>
>>> >>> a, b, c = (line.split(':'))
>>> if line could have less than three fields?
>
>> I asked a very similar question a few weeks ago, and from the various
>> suggestions, I came up with this:
>>
>> line = ":BBB"
>> expand = lambda lst,default,minlen : (lst + [default]*minlen)[0:minlen]
>> a,b,c = expand( line.split(":"), "", 3 )
>
> Here is an expand() variant that is not restricted to lists but works with
> arbitrary iterables:
>
> from itertools import chain, repeat, islice
>
> def expand(iterable, length, default=None):
> return islice(chain(iterable, repeat(default)), length)
Also nice, IMHO, is allowing individual defaults for different positions in
the tuple:
>>> def expand(items, defaults):
... if len(items) >= len(defaults):
... return items[:len(defaults)]
... return items + defaults[len(items):]
...
>>> expand((1, 2, 3), (10, 20, 30, 40))
(1, 2, 3, 40)
>>> expand((1, 2, 3), (10, 20))
(1, 2)
Peter
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Re: default value in a list
TB <[EMAIL PROTECTED]> wrote:
> Is there an elegant way to assign to a list from a list of unknown
> size? For example, how could you do something like:
>
> >>> a, b, c = (line.split(':'))
> if line could have less than three fields?
You could use this old trick...
a, b, c = (line+"::").split(':')[:3]
Or this version if you want something other than "" as the default
a, b, b = (line.split(':') + 3*[None])[:3]
BTW This is a feature I miss from perl...
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Re: default value in a list
Nick Craig-Wood <[EMAIL PROTECTED]> wrote:
...
> Or this version if you want something other than "" as the default
>
> a, b, b = (line.split(':') + 3*[None])[:3]
Either you mean a, b, c -- or you're being subtler than I'm grasping.
> BTW This is a feature I miss from perl...
Hmmm, I understand missing the ``and all the rest goes here'' feature
(I'd really love it if the rejected
a, b, *c = whatever
suggestion had gone through, ah well), but I'm not sure what exactly
you'd like to borrow instead -- blissfully by now I've forgotten a lot
of the perl I used to know... care to clarify?
Alex
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Re: default value in a list
On Fri, 21 Jan 2005 17:04:11 -0800, Jeff Shannon <[EMAIL PROTECTED]> wrote:
>TB wrote:
>
>> Hi,
>>
>> Is there an elegant way to assign to a list from a list of unknown
>> size? For example, how could you do something like:
>>
>>
> a, b, c = (line.split(':'))
>>
>> if line could have less than three fields?
>
>(Note that you're actually assigning to a group of local variables,
>via tuple unpacking, not assigning to a list...)
>
>One could also do something like this:
>
> >>> l = "a:b:c".split(':')
> >>> a, b, c, d, e = l + ([None] * (5 - len(l)))
> >>> print (a, b, c, d, e)
>('a', 'b', 'c', None, None)
> >>>
Or
>>> a, b, c, d, e = ('a:b:c'.split(':')+[None]*4)[:5]
>>> print (a, b, c, d, e)
('a', 'b', 'c', None, None)
You could even be profligate and use *5 in place of that *4,
if that makes an easier idiom ;-)
Works if there's too many too:
>>> a, b = ('a:b:c'.split(':')+[None]*2)[:2]
>>> print (a, b)
('a', 'b')
>
>Personally, though, I can't help but think that, if you're not certain
>how many fields are in a string, then splitting it into independent
>variables (rather than, say, a list or dict) *cannot* be an elegant
>solution. If the fields deserve independent names, then they must
>have a definite (and distinct) meaning; if they have a distinct
>meaning (as opposed to being a series of similar items, in which case
>you should keep them in a list), then which field is it that's
>missing? Are you sure it's *always* the last fields? This feels to
>me like the wrong solution to any problem.
>
>Hm, speaking of fields makes me think of classes.
>
> >>> class LineObj:
>... def __init__(self, a=None, b=None, c=None, d=None, e=None):
>... self.a = a
>... self.b = b
>... self.c = c
>... self.d = d
>... self.e = e
>...
> >>> l = "a:b:c".split(':')
> >>> o = LineObj(*l)
> >>> o.__dict__
>{'a': 'a', 'c': 'c', 'b': 'b', 'e': None, 'd': None}
> >>>
>
>This is a bit more likely to be meaningful, in that there's almost
>certainly some logical connection between the fields of the line
>you're splitting and keeping them as a class demonstrates that
>connection, but it still seems a bit smelly to me.
>
That gives me an idea:
>>> def foo(a=None, b=None, c=None, d=None, e=None, *ignore):
... return a, b, c, d, e
...
>>> a, b, c, d, e = foo(*'a:b:c'.split(':'))
>>> print (a, b, c, d, e)
('a', 'b', 'c', None, None)
But then, might as well do:
>>> def bar(nreq, *args):
... if nreq <= len(args): return args[:nreq]
... return args+ (nreq-len(args))*(None,)
...
>>> a, b, c, d, e = bar(5, *'a:b:c'.split(':'))
>>> print (a, b, c, d, e)
('a', 'b', 'c', None, None)
>>> a, b = bar(2, *'a:b:c'.split(':'))
>>> print (a, b)
('a', 'b')
>>> a, b, c = bar(3, *'a:b:c'.split(':'))
>>> print (a, b, c)
('a', 'b', 'c')
But usually, I would like n + tail, where I know n is a safe bet, e.g.,
>>> def ntail(n, *args):
... return args[:n]+(args[n:],)
...
>>> a, b, t = ntail(2, *'a:b:c:d:e'.split(':'))
>>> print (a, b, t)
('a', 'b', ('c', 'd', 'e'))
>>> a, b, t = ntail(2, *'a:b'.split(':'))
>>> print (a, b, t)
('a', 'b', ())
People have asked to be able to spell that as
a, b, *t = 'a:b:c:d:e'.split(':')
Regards,
Bengt Richter
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Re: default value in a list
Alex Martelli <[EMAIL PROTECTED]> wrote:
> Nick Craig-Wood <[EMAIL PROTECTED]> wrote:
> ...
> > Or this version if you want something other than "" as the default
> >
> > a, b, b = (line.split(':') + 3*[None])[:3]
>
> Either you mean a, b, c -- or you're being subtler than I'm
> grasping.
Just a typo - I meant c!
> > BTW This is a feature I miss from perl...
>
> Hmmm, I understand missing the ``and all the rest goes here'' feature
> (I'd really love it if the rejected
> a, b, *c = whatever
> suggestion had gone through, ah well), but I'm not sure what exactly
> you'd like to borrow instead -- blissfully by now I've forgotten a lot
> of the perl I used to know... care to clarify?
I presume your construct above is equivalent to
my ($a, $b, @c) = split /.../;
which I do indeed miss.
Sometimes I miss the fact that in the below any unused items are set
to undef, rather than an exception being raised
my ($a, $b, $c) = @array;
However, I do appreciate the fact (for code reliability) that the
python equivalent
a, b, c = array
will blow up if there aren't exactly 3 elements in array.
So since I obviously can't have my cake an eat it here, I'd leave
python how it is for the second case, and put one of the suggestions
in this thread into my toolbox / the standard library.
BTW I've converted a lot of perl programs to python so I've come
across a lot of little things like this!
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Re: default value in a list
Alex Martelli wrote:
[explanation and the following code:]
>>> a, b, c = it.islice(
... it.chain(
... line.split(':'),
... it.repeat(some_default),
... ),
... 3)
...
...
>>> def pad_with_default(N, iterable, default=None):
... it = iter(iterable)
... for x in it:
... if N<=0: break
... yield x
... N -= 1
... while N>0:
... yield default
... N -= 1
Why not put these together and put it in itertools, since the requirement seems
to crop up every other week?
>>> line = "A:B:C".split(":")
...
>>> def ipad(N,iterable, default = None):
... return it.islice(it.chain(iterable, it.repeat(default)), N)
...
>>> a,b,c,d = ipad(4,line)
>>> a,b,c,d
('A', 'B', 'C', None)
Michael
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Re: default value in a list
Michael Spencer wrote:
> Alex Martelli wrote:
> [explanation and the following code:]
>
>> >>> a, b, c = it.islice(
>> ... it.chain(
>> ... line.split(':'),
>> ... it.repeat(some_default),
>> ... ),
>> ... 3)
>> ...
>> ...
>> >>> def pad_with_default(N, iterable, default=None):
>> ... it = iter(iterable)
>> ... for x in it:
>> ... if N<=0: break
>> ... yield x
>> ... N -= 1
>> ... while N>0:
>> ... yield default
>> ... N -= 1
>
> Why not put these together and put it in itertools, since the requirement
> seems
> to crop up every other week?
>
> >>> line = "A:B:C".split(":")
> ...
> >>> def ipad(N,iterable, default = None):
> ... return it.islice(it.chain(iterable, it.repeat(default)), N)
> ...
> >>> a,b,c,d = ipad(4,line)
> >>> a,b,c,d
> ('A', 'B', 'C', None)
Good idea!
(+1 if this was posted on python-dev!)
Reinhold
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Re: default value in a list
Reinhold Birkenfeld wrote:
Why not put these together and put it in itertools, since the requirement seems
to crop up every other week?
>>> line = "A:B:C".split(":")
...
>>> def ipad(N,iterable, default = None):
... return it.islice(it.chain(iterable, it.repeat(default)), N)
...
>>> a,b,c,d = ipad(4,line)
>>> a,b,c,d
('A', 'B', 'C', None)
Good idea!
(+1 if this was posted on python-dev!)
Please, please Google the python-dev archives before doing so ;)
Cheers,
Nick.
I seem to recall 'tuple unpacking' as the appropriate phrase. . .
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Re: default value in a list
Nick Coghlan wrote:
> Reinhold Birkenfeld wrote:
>>>Why not put these together and put it in itertools, since the requirement
>>>seems
>>>to crop up every other week?
>>>
>>> >>> line = "A:B:C".split(":")
>>> ...
>>> >>> def ipad(N,iterable, default = None):
>>> ... return it.islice(it.chain(iterable, it.repeat(default)), N)
>>> ...
>>> >>> a,b,c,d = ipad(4,line)
>>> >>> a,b,c,d
>>>('A', 'B', 'C', None)
>>
>>
>> Good idea!
>>
>> (+1 if this was posted on python-dev!)
>
> Please, please Google the python-dev archives before doing so ;)
I have no intent of doing so, I would leave that to more experienced
people...
Reinhold ;)
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Re: default value in a list
Thanks very much for all the responses. They were useful to me and I'll probably refer back to them again in the future. TB -- http://mail.python.org/mailman/listinfo/python-list
Re: Default value for Listbox (Tkinter)
Harlin Seritt wrote: Whenever I set up something similar: vals = ['1', '2','3'] for v in vals: listbox.inset(END, v) I notice that when this listbox is displayed, there is never a default value. How can I make sure that one of the indices is selected by default? Hi Harlin, you must use the select_set method of the listbox. --- from Tkinter import * root = Tk() listbox = Listbox(root) listbox.pack() vals = ['1', '2','3'] for v in vals: listbox.insert(END, v) listbox.select_set(0) # sets the first element root.mainloop() --- Some good resources for Tkinter: http://www.pythonware.com/library/tkinter/introduction/index.htm http://infohost.nmt.edu/tcc/help/pubs/tkinter/ HTH Jørgen Cederberg -- http://mail.python.org/mailman/listinfo/python-list
Re: Default value for Listbox (Tkinter)
Thanks Jorgen! I was reading the Tkinter tutorial (I was looking at this particular page: http://www.pythonware.com/library/tkinter/introduction/x5513-methods.htm) and saw this for select_set(): select_set(index), select_set(first, last) Add one or more items to the selection. I think this was why I overlooked it. The description for it says the listbox adds one or more items to a selection. I would think the description should say the listbox sets the index or element. Thanks again, Harlin -- http://mail.python.org/mailman/listinfo/python-list
Re: default value for list access?
To clearify the problem: The data is the count of something, for example a[90]=10. a may be a dictionary if the range is huge and a list when the range is reasonably small. In the dictionary case, I can use a.setdefault(80, 0) if key 80 does not exist. In the list case, I have to check the length of list before I access it (or use exception). This becomes troublesome when I need to do the following a lot. b = a[80][1] + a[80][2] + a[80][3] If I use the getItem function in my previous email, it will look like b = getItem(getItem(a, 80, []), 1, 0) + getItem(getItem(a, 80, []), 2, 0) + getItem(getItem(a, 80, []), 3, 0) What would be the best solution to handle this? Something like b = df( a[80][1], 0) + df( a[80][2], 0) + df( a[80][3], 0) would be reasonable but df can not be easily defined since the exception will be raised before function df is called. Something like b = df( a, [80, 1], 0) + df( a, [80,2], 0) + df( a, [80, 3], 0) would work if df is defined as def df(a, idx, default): try: for i in range(0, idx): a = a[ idx[i] ] return a except: return 0 but I am afraid that a for loop would bring serious performance problem. Thanks. Bo -- http://mail.python.org/mailman/listinfo/python-list
Re: default value for list access?
Bo Peng wrote: The data is the count of something, for example a[90]=10. a may be a dictionary if the range is huge and a list when the range is reasonably small. In the dictionary case, I can use a.setdefault(80, 0) if key 80 does not exist. In the list case, I have to check the length of list before I access it (or use exception). This becomes troublesome when I need to do the following a lot. b = a[80][1] + a[80][2] + a[80][3] If I use the getItem function in my previous email, it will look like b = getItem(getItem(a, 80, []), 1, 0) + getItem(getItem(a, 80, []), 2, 0) + getItem(getItem(a, 80, []), 3, 0) What would be the best solution to handle this? Sounds to me like the best solution is to simplify the implementation and dispense with the list alternative. Why use a list if a dictionary is suitable? Don't say performance: that's premature optimization. Dictionaries already have what you need, apparently, with setdefault(), so just use them and keep the code simple. ... but I am afraid that a for loop would bring serious performance problem. More premature optimization? The first rule of programming should be to make it work. Then consider making it faster, but only if it is really unacceptably slow. (Some would say to make it work, then make it "right", then make it fast. In this case, "right" doesn't mean "correct" (that's the first step), it means making it clean and simple. Doing it this way makes sense only if you have a really good test suite developed along with the code, ala test-driven development. Lacking that, you should focus on "right" and working together, which in this case suggests leaving out the complicated list option.) -Peter -- http://mail.python.org/mailman/listinfo/python-list
Re: default value for list access?
Ð ÐÑÐ, 27/02/2005 Ð 14:03 -0600, Bo Peng ÐÐÑÐÑ: > To clearify the problem: > > The data is the count of something, for example a[90]=10. a may be a > dictionary if the range is huge and a list when the range is reasonably > small. In the dictionary case, I can use a.setdefault(80, 0) if key 80 > does not exist. In the list case, I have to check the length of list > before I access it (or use exception). > > This becomes troublesome when I need to do the following a lot. > >b = a[80][1] + a[80][2] + a[80][3] > > If I use the getItem function in my previous email, it will look like > >b = getItem(getItem(a, 80, []), 1, 0) + getItem(getItem(a, 80, []), > 2, 0) + getItem(getItem(a, 80, []), 3, 0) > > What would be the best solution to handle this? Something like > >b = df( a[80][1], 0) + df( a[80][2], 0) + df( a[80][3], 0) > > would be reasonable but df can not be easily defined since the exception > will be raised before function df is called. Something like > >b = df( a, [80, 1], 0) + df( a, [80,2], 0) + df( a, [80, 3], 0) > > would work if df is defined as > > def df(a, idx, default): >try: > for i in range(0, idx): >a = a[ idx[i] ] > return a >except: > return 0 > > but I am afraid that a for loop would bring serious performance problem. > > Thanks. > > Bo I'm not sure if that's suitable for you, but you could define your own subclasses for 'dict' and 'list' and specify your specific behaviour you would like. For dict something like this: class MyDict(dict): def __getitem__(self, key): try: return super(MyDict, self).__getitem__(key) except: return 0 a = MyDcit() Ruslan -- http://mail.python.org/mailman/listinfo/python-list
Re: default value for list access?
Sounds to me like the best solution is to simplify the implementation
and dispense with the list alternative. Why use a list if a dictionary
is suitable? Don't say performance: that's premature optimization.
Dictionaries already have what you need, apparently, with setdefault(),
so just use them and keep the code simple.
You are right that if I use all dictionaries, I can use
a.setdefault(4,{}).setdefault(2,0)
to access a[4][2]. Not too bad compared to the getItem function.
However, this is an scientific application. Data are stored internally
in C format and exposed to Python as python array (arraymodule). I guess
the best way is to modify the arraymodule interface and stop it from
raising an exception when index is out of range. (similar to Ruslan's
solution). But this means too much trouble for now.
I will use the df(a, idx, default) method and see if its performance is
acceptable.
Thanks.
Bo
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Re: Providing 'default' value with raw_input()?
planetthoughtful wrote:
> I'm wondering if it's possible, using raw_input(), to provide a
> 'default' value with the prompt?
>
def get_input_with_default(default, prompt=">>> "):
result = raw_input('['+str(default)+'] '+str(prompt))
if result == "": result = default
return default
> I would like to include the ability to edit an existing value (drawn
> from an SQLite table) using a DOS console Python app, but my gut
> feeling from reading what I can find about raw_input() is that it only
> allows you to provide a prompt, not a default value as well.
>
I think it is the editing part that is going to give you a hard time.
curses and readline might be some help if you were on a Unix platform.
I can't think of any way to provided a editable value at the dos
prompt.
All the best,
Keir.
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Re: Providing 'default' value with raw_input()?
planetthoughtful wrote:
> Hi All,
>
> As always, my posts come with a 'Warning: Newbie lies ahead!'
> disclaimer...
>
> I'm wondering if it's possible, using raw_input(), to provide a
> 'default' value with the prompt?
>
> I would like to include the ability to edit an existing value (drawn
> from an SQLite table) using a DOS console Python app, but my gut
> feeling from reading what I can find about raw_input() is that it only
> allows you to provide a prompt, not a default value as well.
>
> If anyone can give me any advice on how I might achieve this, I would
> be immensely appreciative!
>
> Many thanks and much warmth,
>
> planetthoughtful
>
You need to define your own function, with a default argument that gives
the value. You can make it work just like raw_input if no default value
is provided. Something like:
>>> def raw_default(prompt, dflt=None):
... if dflt:
... prompt = "%s [%s]: " % (prompt, dflt)
... res = raw_input(prompt)
... if not res and dflt:
... return dflt
... return res
...
>>> raw_default("How many beans make five", '5')
How many beans make five [5]: six
'six'
>>> raw_default("How many beans make five")
How many beans make fiveten
'ten'
>>> raw_default("How many beans make five", '5')
How many beans make five [5]:
'5'
regards
Steve
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Re: Providing 'default' value with raw_input()?
Hi Steve, As keir mentioned, my goal is to be able to edit the value returned from a record stored in SQLite, so that it can be updated with the new value. To give a little background: as a learning exercise I'm writing a command line app that will allow me to quickly capture todo items (based on a similar concept used by an app for the Mac described on 43folders.com). I have the functionality working for adding todo items, and listing items by various criteria, and updating the status of items, but haven't included any functionality for being able to edit items. It seems, according to kier, that this simply can't be done via the command line in DOS, which is a shame. Sorry I didn't explain myself very well in my original post. Much warmth, planetthoughtful -- http://mail.python.org/mailman/listinfo/python-list
Re: Providing 'default' value with raw_input()?
So you are saying that something like this would not work for you?
current_record_value = get_value_in_database ('record_key')
new_record_value = raw_default ("Enter new record value",
current_record_value)
set_value_in_database ('record_key', new_record_value)
Maybe you are confusing this with TAB completion at the shell command
line.
I often use my own default_input function. I also add the ability to
HELP text
to the prompt, so if the user enters '?' then extra information is
printed.
Of course, that means
Yours,
Noah
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Re: Providing 'default' value with raw_input()?
planetthoughtful wrote: > It seems, according to keir, that this simply can't be done via the > command line in DOS, which is a shame. Now, I said I couldn't think of a way to do it - not that it wasn't possible :-) If you don't need you program to be portable you can use extensions - in this case I would expect you need readline for windows, and ctypes (because readline for windows needs ctypes). You can fetch readline from http://sourceforge.net/project/showfiles.php?group_id=82407 and ctypes from http://sourceforge.net/project/showfiles.php?group_id=71702 I can't promise these will work (all my python has to be 'pure' and cross platform so I've never used readline or rlcompleter) but functions like insert_text look to be in the right area for what (I think) you want. Good luck! Keir. -- http://mail.python.org/mailman/listinfo/python-list
Re: Providing 'default' value with raw_input()?
On 22 Dec 2005 08:55:17 -0800, "planetthoughtful" <[EMAIL PROTECTED]> wrote: >Hi All, > >As always, my posts come with a 'Warning: Newbie lies ahead!' >disclaimer... > >I'm wondering if it's possible, using raw_input(), to provide a >'default' value with the prompt? Sure, depending on what you mean ;-) You can only get a prompt string printed to the screen with raw_input, but you can build that string any way you want, so it can show e.g., User-friendly prose and the current value and a default value and anything else. Then the user has to enter zero or more characters and press Enter. Whether something changes value or not, and what value is used, depends on what the program does with the string (possibly empty) that the user typed. So you have to decide what user response should mean "change old value to default as shown" and what should mean "make no change" and what should mean "convert the typed string to a value and change the old value to that. To have a user-friendly program, you won't want to make user errors too easy, and you will probably want to have the program re-prompt if there is an input typo (or maybe an input that converts ok but has bad business consequences (e.g., like that recent Japanese stock sale switcheroo of price and number of shares that cost many megabucks). > >I would like to include the ability to edit an existing value (drawn >from an SQLite table) using a DOS console Python app, but my gut >feeling from reading what I can find about raw_input() is that it only >allows you to provide a prompt, not a default value as well. > What's wrong with showing the default in the prompt itself? The thing is what user input in response should signify the default? E.g., maybe a single period by itself could mean "use the default" and nothing could mean "no change" and other input would be a new value. >If anyone can give me any advice on how I might achieve this, I would >be immensely appreciative! suppose you had some named values in one dict, e.g., >>> for name, price in values.items(): ... while True: # retry until satisfied ... uresp = raw_input( ... '\n' ... 'Current price of %s is $%.2f %s\n' ... 'Press Enter to leave as is, or\n' ... 'type "D" (without quotes) followed by Enter to change price to %.2f,\n' ... 'or enter a new value: ' % (name, price, info[name][0], info[name][1])) ... if not uresp: break ... if uresp=='D': values[name] = info[name][1]; break ... else: ... try: values[name] = type(values[name])(uresp); break ... except Exception, e: ... print '%s: %s'%(e.__class__.__name__, e) ... print 'Try again' ... Current price of yoghurt is $0.90 each Press Enter to leave as is, or type "D" (without quotes) followed by Enter to change price to 1.19, or enter a new value: D Current price of banana is $0.79 per pound Press Enter to leave as is, or type "D" (without quotes) followed by Enter to change price to 0.99, or enter a new value: Current price of apple is $1.29 per pound Press Enter to leave as is, or type "D" (without quotes) followed by Enter to change price to 1.49, or enter a new value: 1..23 ValueError: invalid literal for float(): 1..23 Try again Current price of apple is $1.29 per pound Press Enter to leave as is, or type "D" (without quotes) followed by Enter to change price to 1.49, or enter a new value: 1.23 >>> Ok, now we can see what happened: >>> for name, price in values.items(): print '%10s: %.2f'%(name,price) ... yoghurt: 1.19 banana: 0.79 apple: 1.23 I'm not suggesting this as a pattern to follow, just to illustrate what you can do with raw_input. IOW, it's about how you build the prompt string, and what you do with the user response input string that solves your problem. Voluminous prompts get old fast, so you might e.g. want to accept a '?' to get extra context-sensitive info instead, followed by retry. Regards, Bengt Richter -- http://mail.python.org/mailman/listinfo/python-list
Re: Providing 'default' value with raw_input()?
Hi Noah, I can't find any mention of a 'raw_default' function. So, lol, yes I'm kind of saying that it would not work for me (well, it won't unless I can find where / how you sources and implemented that function, bearing in mind this will be running on Windows). Many thanks and much warmth, planetthoughtful -- http://mail.python.org/mailman/listinfo/python-list
Re: Providing 'default' value with raw_input()?
Bengt Richter wrote: > On 22 Dec 2005 08:55:17 -0800, "planetthoughtful" <[EMAIL PROTECTED]> wrote: > > >I would like to include the ability to edit an existing value (drawn > >from an SQLite table) using a DOS console Python app, but my gut > >feeling from reading what I can find about raw_input() is that it only > >allows you to provide a prompt, not a default value as well. > > > What's wrong with showing the default in the prompt itself? The thing is > what user input in response should signify the default? E.g., maybe a single > period by itself could mean "use the default" and nothing could mean "no > change" > and other input would be a new value. Hi Bengt, I think that would be a great solution if the value being 'edited' was relatively short, or numeric, etc. But the values I want to 'edit' can be several hundred characters long (ie they're text fields containing todo notes), and using your method, I'd either accept the existing value, or have to retype the text for that record. I think I mislead people when I used the word 'default' -- I meant in the sense of being able to edit the existing value, so that value, out of each record, would be presented as the 'default', available for editing. Sorry for the confusion. Much warmth, planetthoughtful -- http://mail.python.org/mailman/listinfo/python-list
Re: Providing 'default' value with raw_input()?
Hi Kier, Any idea where I'd find documentation on using this extension? I've downloaded and installed, but haven't had any luck finding docs for it. Much warmth, planetthoughtful -- http://mail.python.org/mailman/listinfo/python-list
Re: Providing 'default' value with raw_input()?
planetthoughtful wrote: > Hi Kier, > > Any idea where I'd find documentation on using this extension? I've > downloaded and installed, but haven't had any luck finding docs for it. > As it's a windows version of the standard readline module (usually available on Unix only) I'd _guess_ that you could use the standard library readline documenation, i.e. go to python.org and look up the readline module in the library docs. Cheers, Keir. -- http://mail.python.org/mailman/listinfo/python-list
Re: Providing 'default' value with raw_input()?
planetthoughtful wrote: > I think that would be a great solution if the value being 'edited' was > relatively short, or numeric, etc. But the values I want to 'edit' can > be several hundred characters long (ie they're text fields containing > todo notes), and using your method, I'd either accept the existing > value, or have to retype the text for that record. I think I mislead > people when I used the word 'default' -- I meant in the sense of being > able to edit the existing value, so that value, out of each record, > would be presented as the 'default', available for editing. For fields that long I think a GUI is more appropriate than trying to use command-line editing. You might take a look at easygui - it's textbox is readonly but it looks like it wouldn't be hard to make it editable - or learn enough Tkinter to do it yourself. http://www.ferg.org/easygui/ Kent -- http://mail.python.org/mailman/listinfo/python-list
Re: Providing 'default' value with raw_input()?
If you have Pywin32 build 205 installed, you can use the
win32console module to add the data to the typeahead
buffer before you call raw_input.
import win32console
stdin=win32console.GetStdHandle(win32console.STD_INPUT_HANDLE)
def raw_input_with_default(prompt, default_val):
keypresses=[]
for c in default_val:
evt=win32console.PyINPUT_RECORDType(win32console.KEY_EVENT)
evt.Char=unicode(c)
evt.RepeatCount=1
evt.KeyDown=True
keypresses.append(evt)
stdin.WriteConsoleInput(keypresses)
return raw_input(prompt)
data=raw_input_with_default('modify this: ','some data')
print data
hth
Roger
"planetthoughtful" <[EMAIL PROTECTED]> wrote:
> Hi Steve,
>
> As keir mentioned, my goal is to be able to edit the value returned
> from a record stored in SQLite, so that it can be updated with the new
> value.
>
> To give a little background: as a learning exercise I'm writing a
> command line app that will allow me to quickly capture todo items
> (based on a similar concept used by an app for the Mac described on
> 43folders.com). I have the functionality working for adding todo items,
> and listing items by various criteria, and updating the status of
> items, but haven't included any functionality for being able to edit
> items.
>
> It seems, according to kier, that this simply can't be done via the
> command line in DOS, which is a shame.
>
> Sorry I didn't explain myself very well in my original post.
>
> Much warmth,
>
> planetthoughtful
>
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Re: Providing 'default' value with raw_input()?
On 22 Dec 2005 12:42:36 -0800, "planetthoughtful" <[EMAIL PROTECTED]> wrote:
>
>Bengt Richter wrote:
>> On 22 Dec 2005 08:55:17 -0800, "planetthoughtful" <[EMAIL PROTECTED]> wrote:
>>
>
>> >I would like to include the ability to edit an existing value (drawn
>> >from an SQLite table) using a DOS console Python app, but my gut
>> >feeling from reading what I can find about raw_input() is that it only
>> >allows you to provide a prompt, not a default value as well.
>> >
>> What's wrong with showing the default in the prompt itself? The thing is
>> what user input in response should signify the default? E.g., maybe a single
>> period by itself could mean "use the default" and nothing could mean "no
>> change"
>> and other input would be a new value.
>
>Hi Bengt,
>
>I think that would be a great solution if the value being 'edited' was
>relatively short, or numeric, etc. But the values I want to 'edit' can
>be several hundred characters long (ie they're text fields containing
>todo notes), and using your method, I'd either accept the existing
>value, or have to retype the text for that record. I think I mislead
>people when I used the word 'default' -- I meant in the sense of being
>able to edit the existing value, so that value, out of each record,
>would be presented as the 'default', available for editing.
>
>Sorry for the confusion.
>
If you want to edit text, maybe the best thing is a text editor?
Why not write it into a temp file and start the user's favorite editor
on it, and when done, read the file back into python and delete the temp.
Maybe check whether any changes actually happened before updating the DB.
os.popen{2,3,4} and tempfile module might help.
Regards,
Bengt Richter
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Re: Providing 'default' value with raw_input()?
Bengt Richter <[EMAIL PROTECTED]> wrote: ... > If you want to edit text, maybe the best thing is a text editor? > Why not write it into a temp file and start the user's favorite editor Agreed. There's a recipe for that in the online Python Cookbook, and we edited and enhanced that into the 2nd edition of the printed (O'Reilly) Python Cookbook, too. Alex -- http://mail.python.org/mailman/listinfo/python-list
Re: Providing 'default' value with raw_input()?
My intention is to build a GUI for this app, yes, but given that I'm about a week old in my learning of Python, I thought a command-line app was a better place to start. I'm actually quite surprised at how featured I've managed to make this app all things considered, and now I'm running into things that aren't easy to do in Python (and probably also not easy to do in any scripting language on a Win machine), as opposed to not easy for me to work out. I had thought to build GUIs in wxPython - is Tkinter any easier to learn? Much warmth, planetthoughtful -- http://mail.python.org/mailman/listinfo/python-list
Re: Providing 'default' value with raw_input()?
Thank you for the suggestion, I'll have a look at this as an alternative. I must admit, it seems a little like a 'kludge', though -- but probably a necessary one, given the limitations of the OS. I'm assuming os.popen() keeps track of when the editor closes? Or would I have to manually fire an 'ok, now update the record in the db' event after editing the value? Much warmth, planetthoughtful -- http://mail.python.org/mailman/listinfo/python-list
Re: Providing 'default' value with raw_input()?
planetthoughtful <[EMAIL PROTECTED]> wrote: > Thank you for the suggestion, I'll have a look at this as an > alternative. > > I must admit, it seems a little like a 'kludge', though -- but probably > a necessary one, given the limitations of the OS. Hmmm, what OS? The recipe I mentioned is probably the best approach on Windows, MacOS, Linux, and other Unix variants -- what other OS do you have in mind, that would let you submit to the user hundreds of characters for editing without in fact using an editor? > I'm assuming os.popen() keeps track of when the editor closes? Or would It has to, because it needs to supply all the subprocess's output as the contents of the file object it returns, and it couldn't be sure it has all of the output until the subprocess has finished. There are, of course, other ways to control sub-processes (Python 2.4's subprocess module, in particular). > I have to manually fire an 'ok, now update the record in the db' event > after editing the value? In some situations it may be impractical to rely on the editor closing; for example, the user's favorite editor might be a multitab one that's big, heavy, and slow to start, so that the user doesn't close the whole process but rather just a specific tab. In such cases, unless you can build in some hook specific to the user's favorite editor (so you can know when a specific tab/file is done getting edited), you may end up requiring the user to press enter at your prompt to indicate he or she's done editing, or some such semi-kludge. I cannot think of a sufficiently general solution, given the variety of editors around, to just magically divine the crucial "done with editing" condition... Alex -- http://mail.python.org/mailman/listinfo/python-list
Re: Providing 'default' value with raw_input()?
planetthoughtful wrote: > ... > I had thought to build GUIs in wxPython - is Tkinter any easier to > learn? I certainly found Tkinter easier. There are a couple of good tutorials (and there is always the Grayson book) on the web to get started. What is easiest to learn is (in many cases) a property of the student, however. Were I a Linux-only GPL kind of a guy, I think Qt might be an interesting way to go. One thing that helps tremendously in learning Tkinter: using Idle in single-process mode: C:\Python24\Python C:\Python24\Lib\idlelib\idle.pyw -n This is obviously a WinXX example, but the "-n" parameter to idle is the important part. Since a single-process Idle is running the Tkinter GUI loop, you can try operations a step at a time (letting you see what happens). --Scott David Daniels [EMAIL PROTECTED] -- http://mail.python.org/mailman/listinfo/python-list
Re: Providing 'default' value with raw_input()?
Hi Roger, This is exactly what I was looking for! Thank you so much! I now have a fully functioning command-line todo app. Anyone interested in why I picked that as my 2nd-ever-Python-app might like to read the post over at 43folders.com about suggested uses for Quicksilver on the Mac (http://www.43folders.com/2005/11/21/qs-redux/). I wasn't aware of anything similar on Windows, so it seemed like a good opportunity to build something with similar (and, in fact, better) functionality (at least in terms of the 43folders.com use for Quicksilver) using Python. Anyway, thanks again -- very much appreciate everyone's input! Much warmth, planetthoughtful -- http://mail.python.org/mailman/listinfo/python-list
Re: Providing 'default' value with raw_input()?
planetthoughtful wrote: > My intention is to build a GUI for this app, yes, but given that I'm > about a week old in my learning of Python, I thought a command-line app > was a better place to start. > > I had thought to build GUIs in wxPython - is Tkinter any easier to > learn? Tkinter is quite easy to use for simple apps. Pythoncard is a layer on top of wxPython that makes it easier to use, you might want to look at that. Kent -- http://mail.python.org/mailman/listinfo/python-list
Re: Providing 'default' value with raw_input()?
Alex Martelli wrote: > In some situations it may be impractical to rely on the editor closing; > for example, the user's favorite editor might be a multitab one that's > big, heavy, and slow to start, so that the user doesn't close the whole > process but rather just a specific tab. In such cases, unless you can > build in some hook specific to the user's favorite editor (so you can > know when a specific tab/file is done getting edited), you may end up > requiring the user to press enter at your prompt to indicate he or she's > done editing, or some such semi-kludge. I cannot think of a > sufficiently general solution, given the variety of editors around, to > just magically divine the crucial "done with editing" condition... > > > Alex The ExternalEditor product for Zope does this in a quite clever way - probably not perfect, but it worked for me every time in windows and linux. The product is used to be able to edit any Zope object in an external editor and automatically transfer the edited file from the client to the server after save. The source can be found at http://plope.com/software/ExternalEditor. -- http://mail.python.org/mailman/listinfo/python-list
Difficulty with maxsplit default value for str.split
I'm having problems passing a default value to the maxsplit argument of str.split. I'm trying to write a function which acts as a wrapper to split, something like this: def mysplit(S, sep=None, maxsplit=None): pre_processing() result = S.split(sep, maxsplit) post_processing() return result But the split method doesn't accept a value of None for maxsplit, and I don't know what default value I should be using. Passing 0 as the default isn't correct, because then it splits zero times. By experimentation, I have discovered that passing -1 as the default instead of None *appears* to work, but I'm not sure if I can rely on it or if that is an accidental implementation detail. According to the documentation at http://docs.python.org/lib/string-methods.html#string-methods split([sep [,maxsplit]]) Return a list of the words in the string, using sep as the delimiter string. If maxsplit is given, at most maxsplit splits are done. (thus, the list will have at most maxsplit+1 elements). If maxsplit is not specified, then there is no limit on the number of splits (all possible splits are made). If I take that literally, then the correct way to wrap split is something like this: def mysplit(S, sep=None, maxsplit=None): pre_processing() if maxsplit is None: # don't specify maxsplit result = S.split(sep) else: result = S.split(sep, maxsplit) post_processing() return result Is it safe for me to pass -1 as the default to maxsplit, meaning "unlimited splits"? Should the docs be fixed to mention that? Thanks, -- Steven. -- http://mail.python.org/mailman/listinfo/python-list
Re: Difficulty with maxsplit default value for str.split
Steven, According to the current Python source the default value of maxsplit=-1. I think you can count on that as I don't think there would be a reason to change it in the future. If you are really worried about it then your version of calling a particular version of split should work. By the way, if you use Python 2.5 and when your maxsplit function is called there is a clear common case in regards to maxsplit, you could use the new conditional expression. Say most of the time mysplit is used with a default value of maxsplit, then you can re-write your 'if' code as - result=S.split(sep) if maxsplit is None else S.split(sep,maxsplit) - -Nick Vatamaniuc Steven D'Aprano wrote: > I'm having problems passing a default value to the maxsplit argument of > str.split. I'm trying to write a function which acts as a wrapper to > split, something like this: > > def mysplit(S, sep=None, maxsplit=None): > pre_processing() > result = S.split(sep, maxsplit) > post_processing() > return result > > But the split method doesn't accept a value of None for maxsplit, and I > don't know what default value I should be using. Passing 0 as the default > isn't correct, because then it splits zero times. > > By experimentation, I have discovered that passing -1 as the default > instead of None *appears* to work, but I'm not sure if I can rely on it or > if that is an accidental implementation detail. According to the > documentation at > http://docs.python.org/lib/string-methods.html#string-methods > > split([sep [,maxsplit]]) > Return a list of the words in the string, using sep as the delimiter > string. If maxsplit is given, at most maxsplit splits are done. (thus, > the list will have at most maxsplit+1 elements). If maxsplit is not > specified, then there is no limit on the number of splits (all > possible splits are made). > > > If I take that literally, then the correct way to wrap split is something > like this: > > def mysplit(S, sep=None, maxsplit=None): > pre_processing() > if maxsplit is None: > # don't specify maxsplit > result = S.split(sep) > else: > result = S.split(sep, maxsplit) > post_processing() > return result > > Is it safe for me to pass -1 as the default to maxsplit, meaning > "unlimited splits"? Should the docs be fixed to mention that? > > Thanks, > > > > -- > Steven. -- http://mail.python.org/mailman/listinfo/python-list
Re: Difficulty with maxsplit default value for str.split
Steven D'Aprano wrote: > I'm having problems passing a default value to the maxsplit argument of > str.split. I'm trying to write a function which acts as a wrapper to > split, something like this: > > def mysplit(S, sep=None, maxsplit=None): > pre_processing() > result = S.split(sep, maxsplit) > post_processing() > return result > > But the split method doesn't accept a value of None for maxsplit, and I > don't know what default value I should be using. def mysplit(S, *args): pre_processing() result = S.split(*args) post_processing() return result > Is it safe for me to pass -1 as the default to maxsplit, meaning > "unlimited splits"? not really. -- http://mail.python.org/mailman/listinfo/python-list
Re: Difficulty with maxsplit default value for str.split
Steven D'Aprano <[EMAIL PROTECTED]> writes: > Is it safe for me to pass -1 as the default to maxsplit, meaning > "unlimited splits"? Should the docs be fixed to mention that? Frederik gave a simple and practical solution to your immediate problem, but yes, I think the docs should be fixed after checking the code. -- http://mail.python.org/mailman/listinfo/python-list
Re: Difficulty with maxsplit default value for str.split
On Sun, 24 Sep 2006 10:34:31 +0200, Fredrik Lundh wrote: >> But the split method doesn't accept a value of None for maxsplit, and I >> don't know what default value I should be using. > > def mysplit(S, *args): > pre_processing() > result = S.split(*args) > post_processing() > return result Thanks Fredrik, that's *exactly* the sort of insight I was lacking. And now that you've shown me, I can't believe how obvious it is. -- Steven D'Aprano -- http://mail.python.org/mailman/listinfo/python-list
Using default a empty dictionary as a default value
Dear All,
I ran my code through pylint to clean it up and one of the (many) errors it
through up was
Dangerous default value {} as argument
Bascially, I have:
class NewClass:
def __init__(self, myDict={}):
for key, value in myDict:
print key, value
Obviously, this is not the way it should be done. Should I have a default
value of None for myDict and test for it? Or is there some other way?
Thanks
Colin
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Re: Using default a empty dictionary as a default value
C Gillespie wrote:
> Dear All,
> I ran my code through pylint to clean it up and one of the (many) errors
> it through up was
> Dangerous default value {} as argument
> Bascially, I have:
>
> class NewClass:
> def __init__(self, myDict={}):
> for key, value in myDict:
> print key, value
>
> Obviously, this is not the way it should be done. Should I have a default
> value of None for myDict and test for it? Or is there some other way?
Yes. That's the way to go.
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Diez B. Roggisch
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Re: Using default a empty dictionary as a default value
C Gillespie wrote:
Dear All,
I ran my code through pylint to clean it up and one of the (many) errors it
through up was
Dangerous default value {} as argument
Bascially, I have:
class NewClass:
def __init__(self, myDict={}):
for key, value in myDict:
print key, value
Obviously, this is not the way it should be done. Should I have a default
value of None for myDict and test for it? Or is there some other way?
Take a look at:
http://www.python.org/doc/2.4/tut/node6.html#SECTION00671
look for "Important warning"
HTH
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Re: Using default a empty dictionary as a default value
C Gillespie wrote:
Dear All,
I ran my code through pylint to clean it up and one of the (many) errors it
through up was
Dangerous default value {} as argument
Bascially, I have:
class NewClass:
def __init__(self, myDict={}):
for key, value in myDict:
print key, value
Obviously, this is not the way it should be done. Should I have a default
value of None for myDict and test for it? Or is there some other way?
If you *know* you will not be modifying the contents
of myDict, and you *know* you will not be modifying
the function in the future to do so, then it's
completely safe as written...
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User input with a default value that can be modified
Hello the list :-)
I do a little program that permit the user to manage list of sentences.
This program runs into a linux shell.
The user can add, modify and delete the sentences.
What I want to do is :
When the user want to modify one sentence, I would like to do this :
Modify your sentence : The_sentence_appear_here_followed_by_a_cursor
And the user can go back with the cursor, like in the bash shell,
delete, modify, and when pressing enter, the new value (or the same if
not modified) is put in my variable.
Of course, the first think I did as a newbie was :
new_sentence = raw_input("Modify your sentence : "old_sentence)
But OF COURSE, stupid am I, the user cannot put the cursor back into
the old sentence !
I think about playing with some sophisticated keyboard exercise where
I could program a new input command with a value already appearing as
answer, but I am pretty sure that it exists already.
What do you think about it ?
Actually, it is quite difficult to find anything on it, because the
keywords are not very obvious (input, default answer, ...)
Thank you for your help.
Etienne
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Re: User input with a default value that can be modified
On May 28, 11:52 am, "Etienne Hilson" <[EMAIL PROTECTED]>
wrote:
> Hello the list :-)
>
> I do a little program that permit the user to manage list of sentences.
> This program runs into a linux shell.
> The user can add, modify and delete the sentences.
>
> What I want to do is :
>
> When the user want to modify one sentence, I would like to do this :
>
> Modify your sentence : The_sentence_appear_here_followed_by_a_cursor
>
> And the user can go back with the cursor, like in the bash shell,
> delete, modify, and when pressing enter, the new value (or the same if
> not modified) is put in my variable.
>
> Of course, the first think I did as a newbie was :
>
> new_sentence = raw_input("Modify your sentence : "old_sentence)
>
> But OF COURSE, stupid am I, the user cannot put the cursor back into
> the old sentence !
>
> I think about playing with some sophisticated keyboard exercise where
> I could program a new input command with a value already appearing as
> answer, but I am pretty sure that it exists already.
>
> What do you think about it ?
>
> Actually, it is quite difficult to find anything on it, because the
> keywords are not very obvious (input, default answer, ...)
>
> Thank you for your help.
>
> Etienne
> --
> (\__/)
> (='.'=) Ceci est un petit lapin. Copiez/collez-le dans
> (")_(") votre signature pour l'aider à dominer le monde
Check into the readline module. This is what I came up with. A
second thread injects the text into the open readline instance.
Hopefully the experts will show the _right_ way to do it.
import readline, threading
import time
class write(threading.Thread):
def __init__ (self, s):
threading.Thread.__init__(self)
self.s = s
def run(self):
time.sleep(.01)
readline.insert_text(self.s)
readline.redisplay()
write("Edit this sentence").start()
s = raw_input("prompt:")
print s
~Sean
--
http://mail.python.org/mailman/listinfo/python-list
Re: User input with a default value that can be modified
On May 28, 11:52 am, "Etienne Hilson" <[EMAIL PROTECTED]>
wrote:
> Hello the list :-)
>
> I do a little program that permit the user to manage list of sentences.
> This program runs into a linux shell.
> The user can add, modify and delete the sentences.
>
> What I want to do is :
>
> When the user want to modify one sentence, I would like to do this :
>
> Modify your sentence : The_sentence_appear_here_followed_by_a_cursor
>
> And the user can go back with the cursor, like in the bash shell,
> delete, modify, and when pressing enter, the new value (or the same if
> not modified) is put in my variable.
>
> Of course, the first think I did as a newbie was :
>
> new_sentence = raw_input("Modify your sentence : "old_sentence)
>
> But OF COURSE, stupid am I, the user cannot put the cursor back into
> the old sentence !
>
> I think about playing with some sophisticated keyboard exercise where
> I could program a new input command with a value already appearing as
> answer, but I am pretty sure that it exists already.
>
> What do you think about it ?
>
> Actually, it is quite difficult to find anything on it, because the
> keywords are not very obvious (input, default answer, ...)
>
> Thank you for your help.
>
> Etienne
> --
> (\__/)
> (='.'=) Ceci est un petit lapin. Copiez/collez-le dans
> (")_(") votre signature pour l'aider à dominer le monde
Check into the readline module. This is what I came up with. A
second thread injects the text into the open readline instance.
Hopefully the experts will show the _right_ way to do it.
import readline, threading
import time
class write(threading.Thread):
def __init__ (self, s):
threading.Thread.__init__(self)
self.s = s
def run(self):
time.sleep(.01)
readline.insert_text(self.s)
readline.redisplay()
write("Edit this sentence").start()
s = raw_input("prompt:")
print s
~Sean
--
http://mail.python.org/mailman/listinfo/python-list
