Re: Why use "locals()"
On Sep 18, 9:55 am, Simon Forman wrote: > On Mon, Sep 14, 2009 at 1:12 AM, Sean DiZazzo wrote: > > > Thanks for your explanation Steven. I see how it can be valuable, but > > it seems to always break the second rule of Zen. I don't really want > > to get into the code of debuggers, but I guess I can see how they > > might have no other way to know what local variables have been set. > > > ~Sean > > The zeroth "rule" of zen is "don't take the rules so seriously". > "They're really more like guidelines anyway." > > Regards, > ~simon Yeah. I think I was just a bit randy at that moment. I realized that the (*args,**kwargs) idiom is very similar and I use it all the time. ~Sean -- http://mail.python.org/mailman/listinfo/python-list
Re: Why use "locals()"
On Mon, Sep 14, 2009 at 1:12 AM, Sean DiZazzo wrote: > > Thanks for your explanation Steven. I see how it can be valuable, but > it seems to always break the second rule of Zen. I don't really want > to get into the code of debuggers, but I guess I can see how they > might have no other way to know what local variables have been set. > > ~Sean The zeroth "rule" of zen is "don't take the rules so seriously". "They're really more like guidelines anyway." Regards, ~simon -- http://mail.python.org/mailman/listinfo/python-list
Re: Why use "locals()"
Sion Arrowsmith wrote: Gabriel Genellina wrote: escribi�: What I'm not clear about is under what circumstances locals() does not produce the same result as vars() . py> help(vars) Help on built-in function vars in module __builtin__: vars(...) vars([object]) -> dictionary Without arguments, equivalent to locals(). With an argument, equivalent to object.__dict__. Meh, that's what I get for trying to make sense of http://docs.python.org/library/functions.html#vars -- which implies the above, but isn't explicit about it -- rather than using help. In particular, the docs for locals talk about the inclusion of free variables in functions, which is absent for vars, which might imply that there is a difference. I believe the 'free var' stuff is a doc error, so I filed http://bugs.python.org/issue6925 Doc for locals and vars tjr -- http://mail.python.org/mailman/listinfo/python-list
Re: Why use "locals()"
On 09/14/2009 08:36 AM, Sean DiZazzo wrote: I have never used a call to "locals()" in my code. Can you show me a use case where it is valuable and Pythonic? You've received other answers, but just purely from the 'zen' perspective, there is a nice clean yin/yan symmetry about globals() Vs locals() after all... Namespaces are one honking great idea -- let's do more of those! I am sure someone can come up with an example of where having this very distinction is useful ...I am too lazy to dream up one myself right now. cheers, - steve -- random non tech spiel: http://lonetwin.blogspot.com/ tech randomness: http://lonehacks.blogspot.com/ what i'm stumbling into: http://lonetwin.stumbleupon.com/ -- http://mail.python.org/mailman/listinfo/python-list
Re: Why use "locals()"
Gabriel Genellina wrote: > escribió: >> What I'm not clear about is under what circumstances locals() does >> not produce the same result as vars() . > >py> help(vars) >Help on built-in function vars in module __builtin__: > >vars(...) > vars([object]) -> dictionary > > Without arguments, equivalent to locals(). > With an argument, equivalent to object.__dict__. Meh, that's what I get for trying to make sense of http://docs.python.org/library/functions.html#vars -- which implies the above, but isn't explicit about it -- rather than using help. In particular, the docs for locals talk about the inclusion of free variables in functions, which is absent for vars, which might imply that there is a difference. -- \S under construction -- http://mail.python.org/mailman/listinfo/python-list
Re: Why use "locals()"
On Sep 15, 11:41 am, "Gabriel Genellina" wrote: > En Tue, 15 Sep 2009 11:18:35 -0300, Sion Arrowsmith > escribió: > > > Sean DiZazzo wrote: > > What I'm not clear about is under what circumstances locals() does > > not produce the same result as vars() . > > py> help(vars) > Help on built-in function vars in module __builtin__: > > vars(...) > vars([object]) -> dictionary > > Without arguments, equivalent to locals(). > With an argument, equivalent to object.__dict__. Now *this* I would say is unPythonic: it's basically another obvious way to do something with no additional benefits. It'd be more useful (and less of a misnomer) if it would return an object really repesenting the variable visibility at the current scope, something like "globals().copy().update(locals())", while taking care of edge cases like undeclared locals. Carl Banks -- http://mail.python.org/mailman/listinfo/python-list
Re: Why use "locals()"
En Tue, 15 Sep 2009 11:18:35 -0300, Sion Arrowsmith escribió: Sean DiZazzo wrote: What I'm not clear about is under what circumstances locals() does not produce the same result as vars() . py> help(vars) Help on built-in function vars in module __builtin__: vars(...) vars([object]) -> dictionary Without arguments, equivalent to locals(). With an argument, equivalent to object.__dict__. -- Gabriel Genellina -- http://mail.python.org/mailman/listinfo/python-list
Re: Why use "locals()"
Sean DiZazzo wrote:
>> def print_item(item):
>> description = textwrap.fill(item.description, 40)
>> short = item.description.split('\n', 1)[0]
>> code = str(item.id).zfill(6)
>> print "%(code)s %(short)s\n%(description)s\n" % locals()
>
>I see the use of that, but according to Zen, "Explicit is better than
>implicit."
I'm having trouble imaginging what a "more explicit" version would be.
I use this idiom a lot for code generation, finding it much more
readable than:
"%s %s\n%s\n" % (code, short, description)
or even:
code + ' ' + short + '\n' + description + '\n'
What I'm not clear about is under what circumstances locals() does
not produce the same result as vars() .
--
\S
under construction
--
http://mail.python.org/mailman/listinfo/python-list
Re: Why use "locals()"
Given that python is devoid of types: "Is the variable 'a' an int or a float at runtime?", explicit can only be taken so far. Personally, I use locals() when I work with Django. On Mon, Sep 14, 2009 at 7:42 AM, Sean DiZazzo wrote: >> If you are willing to open your mind to the possibility that some >> Pythonic things don't adhere to every Zen, then I would suggest that >> Gabrielle's examples are perfectly Pythonic shortcuts. But if you >> don't want to use them, you don't have to, nobody is forcing you. > > It's a pretty small domain, but I see the use (and the Pythonicity). > > Thanks all for your advice. > > ~Sean > -- > http://mail.python.org/mailman/listinfo/python-list > -- http://mail.python.org/mailman/listinfo/python-list
Re: Why use "locals()"
> If you are willing to open your mind to the possibility that some > Pythonic things don't adhere to every Zen, then I would suggest that > Gabrielle's examples are perfectly Pythonic shortcuts. But if you > don't want to use them, you don't have to, nobody is forcing you. It's a pretty small domain, but I see the use (and the Pythonicity). Thanks all for your advice. ~Sean -- http://mail.python.org/mailman/listinfo/python-list
Re: Why use "locals()"
On Sep 13, 10:15 pm, Carl Banks wrote: > Gabrielle's Whoops, very sorry about that typo, just how it rolled of the fingers. Ugh. Carl Banks -- http://mail.python.org/mailman/listinfo/python-list
Re: Why use "locals()"
On Sep 13, 9:54 pm, Sean DiZazzo wrote:
> > > I have never used a call to "locals()" in my code. Can you show me a
> > > use case where it is valuable and Pythonic?
>
> > def print_item(item):
> > description = textwrap.fill(item.description, 40)
> > short = item.description.split('\n', 1)[0]
> > code = str(item.id).zfill(6)
> > print "%(code)s %(short)s\n%(description)s\n" % locals()
>
> I see the use of that, but according to Zen, "Explicit is better than
> implicit."
>
>
>
> > Transferring arguments:
>
> > def foo(some, long, list, of, arguments):
> > additional = 5
> > return other(**locals())
>
> Why not?:
>
> def foo(**kwargs):
> kwargs["additional"] = 5
> return other(**kwargs)
>
> > Defining properties:
>
> > class ColourThing(object):
> > �...@apply
> > def rgb():
> > def fset(self, rgb):
> > self.r, self.g, self.b = rgb
> > def fget(self):
> > return (self.r, self.g, self.b)
> > return property(**locals())
>
> So really it's just a short hand. But it's against the Zen! Explicit
> not Implicit! I'm not convincedthen again, I didn't look at the
> source code of the standard libraries.
ISTM that any use of locals() is going to be labeled "implicit" by
you, which is not unfair, since it pretty much is implicit compared to
using local variables directly.
If being implicit is alone enough to make anything unPythonic, then
the answer to your question is No, locals() is never Pythonic.
If you are willing to open your mind to the possibility that some
Pythonic things don't adhere to every Zen, then I would suggest that
Gabrielle's examples are perfectly Pythonic shortcuts. But if you
don't want to use them, you don't have to, nobody is forcing you.
Carl Banks
--
http://mail.python.org/mailman/listinfo/python-list
Re: Why use "locals()"
On Sep 13, 9:11 pm, Steven D'Aprano
wrote:
> On Sun, 13 Sep 2009 20:26:06 -0700, Sean DiZazzo wrote:
> > On Sep 13, 8:18 pm, Steven D'Aprano
> > wrote:
> >> On Sun, 13 Sep 2009 20:06:51 -0700, Sean DiZazzo wrote:
> >> > I have never used a call to "locals()" in my code. Can you show me a
> >> > use case where it is valuable and Pythonic?
>
> >> grep is your friend:
>
> >> $ grep "locals()" /usr/lib/python2.5/*.py
> >> /usr/lib/python2.5/decimal.py: for name, val in
> >> locals().items(): /usr/lib/python2.5/doctest.py: return
> >> __import__(module, globals(), locals(), ["*"])
> >> /usr/lib/python2.5/profile.py: p.runctx('f(m)', globals(),
> >> locals()) /usr/lib/python2.5/pydoc.py: docloc = ' >> href="%(docloc)s">Module Docs' % locals()
> >> /usr/lib/python2.5/smtpd.py: mod =
> >> __import__(classname[:lastdot], globals(), locals(), [""])
>
> >> --
> >> Steven
>
> > That is not a use case. I still don't understand!
>
> Look at the source code to find out what they're doing with the
> information they extract from locals(), and why.
>
> For instance, profile should be obvious -- debuggers and profilers often
> need to see the values of local names.
>
> pydoc is using the fairly common idiom of injecting the values of
> variables into a string. Personally, I don't see why it uses this idiom:
>
> docloc = 'something'
> docloc = '%(docloc)s' % locals()
>
> instead of this:
>
> docloc = 'something'
> docloc = '%s' % docloc
>
> but for more complicated cases, the first idiom is much simpler.
>
> decimal seems to be using locals() to avoid this anti-pattern:
>
> def __init__(self, a, b, c, d, e, f, g, h):
> self.a = a
> self.b = b
> self.c = c
> self.d = d
> # blah blah blah
> self.h = h
>
> and replacing it with:
>
> def __init__(self, a, b, c, d, e, f, g, h):
> for name, val in locals().items():
> setattr(self, name, val)
> del self.self
>
> Another use-case: if you have a tool that documents Python code
> automatically, it needs a way to automatically view the values of local
> names.
>
> > PS. I know how to use grep.
>
> I'm sure you do. But you didn't think of using grep, which is why I made
> the suggestion that grepping the standard library is a good tool to use
> to search for Pythonic examples of code.
>
> It's not foolproof, e.g. the unittest module is more Java-onic than
> Pythonic, but it's a good start.
>
> --
> Steven
Thanks for your explanation Steven. I see how it can be valuable, but
it seems to always break the second rule of Zen. I don't really want
to get into the code of debuggers, but I guess I can see how they
might have no other way to know what local variables have been set.
~Sean
--
http://mail.python.org/mailman/listinfo/python-list
Re: Why use "locals()"
> > I have never used a call to "locals()" in my code. Can you show me a
> > use case where it is valuable and Pythonic?
>
> def print_item(item):
> description = textwrap.fill(item.description, 40)
> short = item.description.split('\n', 1)[0]
> code = str(item.id).zfill(6)
> print "%(code)s %(short)s\n%(description)s\n" % locals()
I see the use of that, but according to Zen, "Explicit is better than
implicit."
>
> Transferring arguments:
>
> def foo(some, long, list, of, arguments):
> additional = 5
> return other(**locals())
>
Why not?:
def foo(**kwargs):
kwargs["additional"] = 5
return other(**kwargs)
> Defining properties:
>
> class ColourThing(object):
> �...@apply
> def rgb():
> def fset(self, rgb):
> self.r, self.g, self.b = rgb
> def fget(self):
> return (self.r, self.g, self.b)
> return property(**locals())
>
So really it's just a short hand. But it's against the Zen! Explicit
not Implicit! I'm not convincedthen again, I didn't look at the
source code of the standard libraries.
~Sean
--
http://mail.python.org/mailman/listinfo/python-list
Re: Why use "locals()"
En Mon, 14 Sep 2009 00:06:51 -0300, Sean DiZazzo
escribió:
I have never used a call to "locals()" in my code. Can you show me a
use case where it is valuable and Pythonic?
def print_item(item):
description = textwrap.fill(item.description, 40)
short = item.description.split('\n', 1)[0]
code = str(item.id).zfill(6)
print "%(code)s %(short)s\n%(description)s\n" % locals()
Transferring arguments:
def foo(some, long, list, of, arguments):
additional = 5
return other(**locals())
Defining properties:
class ColourThing(object):
@apply
def rgb():
def fset(self, rgb):
self.r, self.g, self.b = rgb
def fget(self):
return (self.r, self.g, self.b)
return property(**locals())
(example taken from this recent thread
http://groups.google.com/group/comp.lang.python/browse_thread/thread/449eb9b835a472e7/
see also this recipe http://code.activestate.com/recipes/576742/ )
--
Gabriel Genellina
--
http://mail.python.org/mailman/listinfo/python-list
Re: Why use "locals()"
On Sun, 13 Sep 2009 20:26:06 -0700, Sean DiZazzo wrote:
> On Sep 13, 8:18 pm, Steven D'Aprano
> wrote:
>> On Sun, 13 Sep 2009 20:06:51 -0700, Sean DiZazzo wrote:
>> > I have never used a call to "locals()" in my code. Can you show me a
>> > use case where it is valuable and Pythonic?
>>
>> grep is your friend:
>>
>> $ grep "locals()" /usr/lib/python2.5/*.py
>> /usr/lib/python2.5/decimal.py: for name, val in
>> locals().items(): /usr/lib/python2.5/doctest.py: return
>> __import__(module, globals(), locals(), ["*"])
>> /usr/lib/python2.5/profile.py: p.runctx('f(m)', globals(),
>> locals()) /usr/lib/python2.5/pydoc.py: docloc = '> href="%(docloc)s">Module Docs' % locals()
>> /usr/lib/python2.5/smtpd.py: mod =
>> __import__(classname[:lastdot], globals(), locals(), [""])
>>
>> --
>> Steven
>
> That is not a use case. I still don't understand!
Look at the source code to find out what they're doing with the
information they extract from locals(), and why.
For instance, profile should be obvious -- debuggers and profilers often
need to see the values of local names.
pydoc is using the fairly common idiom of injecting the values of
variables into a string. Personally, I don't see why it uses this idiom:
docloc = 'something'
docloc = '%(docloc)s' % locals()
instead of this:
docloc = 'something'
docloc = '%s' % docloc
but for more complicated cases, the first idiom is much simpler.
decimal seems to be using locals() to avoid this anti-pattern:
def __init__(self, a, b, c, d, e, f, g, h):
self.a = a
self.b = b
self.c = c
self.d = d
# blah blah blah
self.h = h
and replacing it with:
def __init__(self, a, b, c, d, e, f, g, h):
for name, val in locals().items():
setattr(self, name, val)
del self.self
Another use-case: if you have a tool that documents Python code
automatically, it needs a way to automatically view the values of local
names.
> PS. I know how to use grep.
I'm sure you do. But you didn't think of using grep, which is why I made
the suggestion that grepping the standard library is a good tool to use
to search for Pythonic examples of code.
It's not foolproof, e.g. the unittest module is more Java-onic than
Pythonic, but it's a good start.
--
Steven
--
http://mail.python.org/mailman/listinfo/python-list
Re: Why use "locals()"
On Sep 13, 8:18 pm, Steven D'Aprano
wrote:
> On Sun, 13 Sep 2009 20:06:51 -0700, Sean DiZazzo wrote:
> > I have never used a call to "locals()" in my code. Can you show me a
> > use case where it is valuable and Pythonic?
>
> grep is your friend:
>
> $ grep "locals()" /usr/lib/python2.5/*.py
> /usr/lib/python2.5/decimal.py: for name, val in locals().items():
> /usr/lib/python2.5/doctest.py: return __import__(module, globals(),
> locals(), ["*"])
> /usr/lib/python2.5/profile.py: p.runctx('f(m)', globals(), locals())
> /usr/lib/python2.5/pydoc.py: docloc = ' href="%(docloc)s">Module Docs' % locals()
> /usr/lib/python2.5/smtpd.py: mod = __import__(classname[:lastdot],
> globals(), locals(), [""])
>
> --
> Steven
That is not a use case. I still don't understand!
PS. I know how to use grep.
~Sean
--
http://mail.python.org/mailman/listinfo/python-list
Re: Why use "locals()"
On Sun, 13 Sep 2009 20:06:51 -0700, Sean DiZazzo wrote:
> I have never used a call to "locals()" in my code. Can you show me a
> use case where it is valuable and Pythonic?
grep is your friend:
$ grep "locals()" /usr/lib/python2.5/*.py
/usr/lib/python2.5/decimal.py:for name, val in locals().items():
/usr/lib/python2.5/doctest.py:return __import__(module, globals(),
locals(), ["*"])
/usr/lib/python2.5/profile.py:p.runctx('f(m)', globals(), locals())
/usr/lib/python2.5/pydoc.py:docloc = 'Module Docs' % locals()
/usr/lib/python2.5/smtpd.py:mod = __import__(classname[:lastdot],
globals(), locals(), [""])
--
Steven
--
http://mail.python.org/mailman/listinfo/python-list
Why use "locals()"
I have never used a call to "locals()" in my code. Can you show me a use case where it is valuable and Pythonic? ~Sean -- http://mail.python.org/mailman/listinfo/python-list
