[Tutor] 2.7.3 documentation gripe (feel free to ignore)
6.5. The del http://docs.python.org/reference/simple_stmts.html#del statement *del_stmt* ::= del target_list http://docs.python.org/reference/simple_stmts.html#grammar-token-target_list Deletion is recursively defined very similar to the way assignment is defined. Rather than spelling it out in full details, here are some hints. === They call this DOCUMENTATION??? it's similar to such and such - you figure it outhere are the hints! Bah! I hope their code is better than the documentation. :-p Ray P.S. Not a request for help - I can find the answers. Just a comment on the documentation in general ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] index of elements in numpy array
Thank you all for the answer. Below, i have pasted a sample code that shows what i am intending to do. The code fails at line 13 as numpy array dnt have a index attribute. 1 #!/usr/bin/env python 2 import numpy as np 3 4 a=np.array([1,2,3,4,5,6,7,8,9,10,11,12]) 5 6 b=np.reshape(a,(3,4)) 7 8 z=[100,101,102,103,104,106,107,108,109,110,111,112] 9 10 # loop over each row 11 for i1, d1 in enumerate(b): 12 # each x in d1 - value in z corresponding to index of x in d1 13 d1=[x-z[d1.index(x)] for x in d1] If d1 is a simple list, i can fetch the index of its element as d1.index(x). So i would like to know how can achieve the same with numpy array. Thanks once again, Bala On Fri, Sep 14, 2012 at 12:39 AM, Dave Angel d...@davea.name wrote: On 09/13/2012 04:16 PM, Bala subramanian wrote: Friends, I have a 2D matrix (a numpy array) and i am looping over each row in the matrix. I would like to know how i can find the index of each element in a while looping a row. Is there any function in numpy. Thanks Perhaps you're asking a more general question. When iterating over a collection, sometimes you not only want the object, but you also want the index you might have used to fetch it. for row in rows: dosomething with row for index, row in enumerate(rows): dosomething with row and with index Now if rows be a list, or whatever numpy decides to call it, then you can manipulate the particular one with rows[index]. -- DaveA -- C. Balasubramanian ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] (2.7.3) Inexplicable change of type
The code:
def split_string(source,splitlist):
idx = 0
while idx len(splitlist):
if splitlist[idx] in source:
source = ' '.join(source.split(splitlist[idx]))
idx += 1
source = source.split(' ')
print source is, source, and its type is, type(source) # --
while '' in
source:# --
source = source.remove('')
return source
out = split_string('Hi! I am your Assistant Instructor, Peter.', '! ,.')
print out
The result:
source is ['Hi', '', 'I', 'am', 'your', 'Assistant', 'Instructor', '',
'Peter', ''] and its type is type 'list'
Traceback (most recent call last):
File /tmp/pytmp.py, line 18, in module
out = split_string('Hi! I am your Assistant Instructor, Peter.', '! ,.')
File /tmp/pytmp.py, line 13, in split_string
while '' in source:
TypeError: argument of type 'NoneType' is not iterable
Between the two arrows, 'source' inexplicably switches from type list
to type NoneType. Why?
Ray
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Re: [Tutor] index of elements in numpy array
Bala subramanian wrote: Thank you all for the answer. Below, i have pasted a sample code that shows what i am intending to do. The code fails at line 13 as numpy array dnt have a index attribute. 1 #!/usr/bin/env python 2 import numpy as np 3 4 a=np.array([1,2,3,4,5,6,7,8,9,10,11,12]) 5 6 b=np.reshape(a,(3,4)) 7 8 z=[100,101,102,103,104,106,107,108,109,110,111,112] 9 10 # loop over each row 11 for i1, d1 in enumerate(b): 12 # each x in d1 - value in z corresponding to index of x in d1 13 d1=[x-z[d1.index(x)] for x in d1] If d1 is a simple list, i can fetch the index of its element as d1.index(x). So i would like to know how can achieve the same with numpy array. How about b - np.array(z[:4]) array([[-99, -99, -99, -99], [-95, -95, -95, -95], [-91, -91, -91, -91]]) (Note that the result may differ from that of your code if d1 contains duplicate values) ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] (2.7.3) Inexplicable change of type
On 14/09/12 18:43, Ray Jones wrote:
Between the two arrows, 'source' inexplicably switches fromtype list
totype NoneType. Why?
source.remove('') does not do what you think it does. Checking the
Fine Manual is always a good idea, or experimentation at the interactive
interpreter:
py source = list('abcd')
py result = source.remove('a')
py result is None
True
py source
['b', 'c', 'd']
The list.remove method operates on the list in place, and like (nearly?)
all such in-place methods, it returns None.
So source = source.remove(' ') replaces source with None instead of the
list, which is then lost.
By the way, at the interactive interpreter you can also say:
help(list.remove)
to read some documentation on the method.
--
Steven
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Re: [Tutor] (2.7.3) Inexplicable change of type
Ray Jones wrote:
source = source.remove('')
list.remove() modifies the list in-place and therefore by convention returns
None:
source = [one, , three]
source.remove()
source
['one', 'three']
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Re: [Tutor] (2.7.3) Inexplicable change of type
On Fri, Sep 14, 2012 at 4:43 AM, Ray Jones crawlz...@gmail.com wrote:
source = source.remove('')
Between the two arrows, 'source' inexplicably switches from type list
to type NoneType. Why?
x = [1,2,3]
result = x.remove(1)
type(result)
type 'NoneType'
x
[2, 3]
Methods that mutate an object typically return None. Just call
remove() without reassignment.
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Re: [Tutor] (2.7.3) Inexplicable change of type
On 09/14/2012 02:07 AM, Steven D'Aprano wrote:
On 14/09/12 18:43, Ray Jones wrote:
Between the two arrows, 'source' inexplicably switches fromtype list
totype NoneType. Why?
source.remove('') does not do what you think it does. Checking the
Fine Manual is always a good idea, or experimentation at the interactive
interpreter:
[...]
So source = source.remove(' ') replaces source with None instead of the
list, which is then lost.
By the way, at the interactive interpreter you can also say:
help(list.remove)
to read some documentation on the method.
I did use the help() on that, but I missed the 'in place' part. That
would explain things! :))
Thanks.
Ray
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Re: [Tutor] (2.7.3) Inexplicable change of type
Thanks for the responses. I knew it had to be something stupid ;)). Ray ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] 2.7.3 documentation gripe (feel free to ignore)
On 14/09/12 17:29, Ray Jones wrote: 6.5. The del http://docs.python.org/reference/simple_stmts.html#del statement [...] They call this DOCUMENTATION??? it's similar to such and such - you figure it outhere are the hints! Bah! I hope their code is better than the documentation. :-p *shrug* Look at the size of the documentation for assignments, two and a half pages. Deletion is almost exactly the same except there is no target on the left hand side of the operator. I'm honestly not sure that there would be any advantage to spelling out in gory detail over a page and a half how del works, but if you think the documentation is lacking, remember that Python is an open-source project and community input is welcome and desired. -- Steven ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] 2.7.3 documentation gripe (feel free to ignore)
On 09/14/2012 02:32 AM, Steven D'Aprano wrote: On 14/09/12 17:29, Ray Jones wrote: 6.5. The del http://docs.python.org/reference/simple_stmts.html#del statement [...] They call this DOCUMENTATION??? it's similar to such and such - you figure it outhere are the hints! I'm honestly not sure that there would be any advantage to spelling out in gory detail over a page and a half how del works, but if you think the documentation is lacking, remember that Python is an open-source project and community input is welcome and desired. Great reply to sour grapes! lol I'll remember that ;). Ray ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] index of elements in numpy array
On Fri, Sep 14, 2012 at 4:36 AM, Bala subramanian bala.biophys...@gmail.com wrote: 10 # loop over each row 11 for i1, d1 in enumerate(b): 12 # each x in d1 - value in z corresponding to index of x in d1 13 d1=[x-z[d1.index(x)] for x in d1] If d1 is a simple list, i can fetch the index of its element as d1.index(x). So i would like to know how can achieve the same with numpy array. In general you don't want to loop over and enumerate a NumPy array. That's a lot slower than using vectorized operations (just like in MATLAB) and broadcasting. See Peter Otten's answer. For an 'index' operation you have a couple of options. To begin with, a test returns a bool array: d = np.array([1,2,1,2,1]) d == 1 array([ True, False, True, False, True], dtype=bool) You can use this bool array to index the source array: d[d == 1] array([1, 1, 1]) d[d == 1] = 3 d array([3, 2, 3, 2, 3]) To get the indexes, use nonzero or where: np.nonzero(d == 2) (array([1, 3]),) np.where(d == 2) (array([1, 3]),) ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Musical note on python
On Thu, Sep 13, 2012 at 8:37 PM, D.V.N.Sarma డి.వి.ఎన్.శర్మ dvnsa...@gmail.com wrote: Error: name data undefined import wave import winsound from cStringIO import StringIO def get_wave(data): f = StringIO() w = wave.open(f, 'w') w.setnchannels(1) # mono w.setsampwidth(2) # 2 bytes w.setframerate(48000) # samples/second w.writeframes(data) return f.getvalue() Then play the sound like this (_untested_): wave_data = get_wave(data) windsound.PlaySound(wave_data, winsound.SND_MEMORY) data is a byte string of packed samples. For example, the function packwave() converts a sequence of floats into a byte string. It assumes the input is in the range [-1.0, 1.0]. It scales this range to [-32767, 32767]. Each scaled value is packed as 2 bytes in little endian order. That means the order is (low byte, high byte). For example, 32767 becomes \xff\x7f, where 0xff (255) is the low byte and 0x7f (127) is the high byte. You can calculate the value as follows: 255 + 127*256 = 32767. Since the format is 2's complement, the next value up, \x00\x80, wraps around to -32768. Then \x01\x80 is -32767, and so on, up to -1 at \xff\xff. http://docs.python.org/library/struct http://en.wikipedia.org/wiki/Endianness http://en.wikipedia.org/wiki/Two%27s_complement ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] is this use or abuse of __getitem__ ?
Hi, I defined a __getitem__ special method in a class that reads a binary data file using a C library. The docstring should clarify the purpose of the method. This works exactly as I intended it, however, the key argument is actually used as an index (it also raises an IndexError when key is greater than the number of records in the file). Am I abusing the __getitem__ method, or is this just a creative way of using it? # Python 2.6.4 (r264:75708, Oct 26 2009, 08:23:19) [MSC v.1500 32 bit (Intel)] on win32 def __getitem__(self, key): This function reports the record of case number key. For example: firstRecord = FileReader(fileName)[0] if not isinstance(key, (int, float)): raise TypeError if abs(key) self.nCases: raise IndexError retcode1 = self.iomodule.SeekNextCase(self.fh, ctypes.c_long(int(key))) self.caseBuffer, self.caseBufferPtr = self.getCaseBuffer() retcode2 = self.iomodule.WholeCaseIn(self.fh, self.caseBufferPtr) record = struct.unpack(self.structFmt, self.caseBuffer.raw) if any([retcode1, retcode2]): raise RuntimeError, Error retrieving record %d [%s, %s] % \ (key, retcodes[retcode1], retcodes[retcode2]) return record Regards, Albert-Jan ~~ All right, but apart from the sanitation, the medicine, education, wine, public order, irrigation, roads, a fresh water system, and public health, what have the Romans ever done for us? ~~ ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] index of elements in numpy array
On 14 September 2012 11:05, eryksun eryk...@gmail.com wrote: On Fri, Sep 14, 2012 at 4:36 AM, Bala subramanian bala.biophys...@gmail.com wrote: 10 # loop over each row 11 for i1, d1 in enumerate(b): 12 # each x in d1 - value in z corresponding to index of x in d1 13 d1=[x-z[d1.index(x)] for x in d1] If d1 is a simple list, i can fetch the index of its element as d1.index(x). So i would like to know how can achieve the same with numpy array. Whether you use a list or a numpy array, iterating over the elements and then trying to get the index of each value from the value itself is inefficient. It's also leads to problems when the array/list contains duplicate values. I think the way to replace your line 13 would be to use: d1 = [x - z[n] for n, x in enumerate(d1)] There is another problem though which is that you're assigning to d1 which is the same name that you've used for your loop variable in the outer loop. This means that you're throwing away the values you compute. Are you hoping that by assigning to d1, the values would get stored in b? Perhaps what you need to do is: b[i1, :] = [x - z[n] for n, x in enumerate(d1)] This way the values will get stored in b. If you actually want them to be stored in another array, say c, then create that array before the loop with c = np.zeros_like(b) If this is what you're trying to do, though you would be better off just using Peter's suggestion: c = b - np.array(z[:b.shape[1]]) so that you don't need a loop at all. In general you don't want to loop over and enumerate a NumPy array. That's a lot slower than using vectorized operations (just like in MATLAB) and broadcasting. See Peter Otten's answer. For an 'index' operation you have a couple of options. To begin with, a test returns a bool array: d = np.array([1,2,1,2,1]) d == 1 array([ True, False, True, False, True], dtype=bool) You can use this bool array to index the source array: d[d == 1] array([1, 1, 1]) d[d == 1] = 3 d array([3, 2, 3, 2, 3]) To get the indexes, use nonzero or where: np.nonzero(d == 2) (array([1, 3]),) np.where(d == 2) (array([1, 3]),) The suggestions above from eryksun are closer to what actually happens when you use the index function on a list, but you should consider whether or not that is really what you want to do. Oscar ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] (2.7.3) Inexplicable change of type
On 9/14/2012 1:43 AM Ray Jones said...
The code:
snip
source = source.remove('')
return source
To round things out, here's one way to do what I expect you're expecting:
r=range(10)
a = r.pop(r.index(4))
a
4
r
[0, 1, 2, 3, 5, 6, 7, 8, 9]
Emile
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Re: [Tutor] is this use or abuse of __getitem__ ?
On Fri, Sep 14, 2012 at 8:16 AM, Albert-Jan Roskam fo...@yahoo.com wrote: Am I abusing the __getitem__ method, or is this just a creative way of using it? No, you're using it the normal way. The item to get can be an index, a key, or even a slice. http://docs.python.org/reference/datamodel.html#object.__getitem__ if not isinstance(key, (int, float)): raise TypeError Instead you could raise a TypeError if not hasattr(key, '__int__') since later you call int(key). if abs(key) self.nCases: raise IndexError You might also want to support slicing. Here's an example: http://stackoverflow.com/a/2936876/205580 ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] (2.7.3) Inexplicable change of type
On Fri, Sep 14, 2012 at 8:37 AM, Emile van Sebille em...@fenx.com wrote:
source = source.remove('')
To round things out, here's one way to do what I expect you're expecting:
r=range(10)
a = r.pop(r.index(4))
a
4
r
[0, 1, 2, 3, 5, 6, 7, 8, 9]
Ray was probably thinking in terms of immutable objects such as strings:
1.replace('1', '2').replace('2', '3')
'3'
Since Python doesn't do in-place operations on strings, it has to
return a new object for each call to replace().
list.pop() returns a value, but Ray doesn't want the value. Splitting
on a single character leaves empty strings between consecutive runs of
the character (or at the edges). For example, splitting 'babbbab' on
'b' returns ['', 'a', '', '', 'a', '']. Ray is looping until all of
the empty strings have been removed from the list. It's a completely
in-place modification.
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Re: [Tutor] is this use or abuse of __getitem__ ?
On 14/09/12 22:16, Albert-Jan Roskam wrote: Hi, I defined a __getitem__ special method in a class that reads a binary data file using a C library. The docstring should clarify the purpose of the method. This works exactly as I intended it, however, the key argument is actually used as an index (it also raises an IndexError whenkey is greater than the number of records in the file). Am I abusing the __getitem__ method, or is this just a creative way of using it? No, that's exactly what __getitem__ is for. It does double-duty for key-lookup in mappings (dict[key]) and index-lookup in sequences (list[index]). You can also support ranges of indexes by accepting a slice argument. Another comment below: # Python 2.6.4 (r264:75708, Oct 26 2009, 08:23:19) [MSC v.1500 32 bit (Intel)] on win32 def __getitem__(self, key): This function reports the record of case numberkey. For example: firstRecord = FileReader(fileName)[0] if not isinstance(key, (int, float)): raise TypeError Floats? Do you actually have have case number (for example) 0.14285714285714285 ? For this case, I think it is reasonable to insist on exactly an int, and nothing else (except possibly a slice object, to support for example obj[2:15]). -- Steven ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] simon game issues
It would appear you're running some form of event loop, such as
wxpython, tkinter, pygame, or whatever. If so, you have to do your
delays using the mechanism that system defines, not using sleep(). As
you've discovered, sleep() stops the whole thread, and that's not what
you want. What you want is to set an event to fire at some measured
time in the future, so the actual waiting is done inside the event loop.
hey i looked at the livewires documentation and pulled up the timer
information. im struggling to figure out how to use its explanation. i
need to use it at 2 different parts of the program. 1st when the game
starts i need to create my sprite objects so they appear before my
animation objects:
red = Sprite(colour = Colours.red, x = 250, y = 255)
games.screen.add(red)
#timer event delay goes here so the animations don't start as soon as
the game is opened, before the coloured sprites as they've been doing.
self.create_animations()
-
i also need a timer event when i display my sequence of animation
objects so they dont show on screen simultaneously. so:
#1st animation
red_animation = Animation(images = c_red, x = 250, y = 255,
repeat_interval = 4, n_repeats = 1)
games.screen.add(red_ani)
red_sound.play()
#Timer event to go here, so next animation in sequence goes after the
timed pause.
#2nd animation
blue_animation = Animation(images = c_blue, x = 373, y = 255,
repeat_interval = 4, n_repeats = 1)
games.screen.add(blue_ani)
blue_sound.play()
do you think you can offer any help how to implement the timer code or
function? i will provide the link to the page, but here's the relevant
code:
Timer
The Timer class is a class you can add to something which is also a
subclass of Object, to make an object that performs actions at regular
intervals. A class which is intended to be used with another class is
called a mix-in. For instance, if you wanted to make a new class of
your own which was a Circle and also a Timer, you would define the
class by saying class MyClass (games.Circle, games.Timer):
• init_timer (interval)
interval is how often the tick method is called, measured in timer
ticks. How long a tick is depends on the fps argument you give to the
Screen‘s mainloop method. Setting fps to 50 means a tick is 1/50 of a
second.
You must call this method emph{after} you have called the init_ method
for the Object subclass you are using.
• stop ()
Stop the timer running. It continues to exist, but doesn’t count any more.
• start ()
Starts the timer again. A full interval will elapse before it ticks.
• get_interval ()
Gets the current interval.
• set_interval (interval)
Sets the current interval.
• tick ()
This method must be supplied by you, by subclassing the Timer class.
http://www.geon.wz.cz/livewires/w-livewires.html
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Re: [Tutor] is this use or abuse of __getitem__ ?
On 14/09/12 22:16, Albert-Jan Roskam wrote: Hi, I defined a __getitem__ special method in a class that reads a binary data file using a C library. The docstring should clarify the purpose of the method. This works exactly as I intended it, however, the key argument is actually used as an index (it also raises an IndexError whenkey is greater than the number of records in the file). Am I abusing the __getitem__ method, or is this just a creative way of using it? No, that's exactly what __getitem__ is for. It does double-duty for key-lookup in mappings (dict[key]) and index-lookup in sequences (list[index]). You can also support ranges of indexes by accepting a slice argument. COOL! I was already wondering how this could be implemented. Dive into Python is pretty exhaustive wrt special methods, but I don't think they mentioned using the slice class. Below is how I did it. Is it recommended to define the geitem() function inside the __getitem__() method? I was thinking I could also define a _getitem() private method. Hmmm, maybe getitem() is redefined over and over again the way I did it now? def __getitem__(self, key): This function reports the record of case number key. For example: firstRecord = SavReader(savFileName)[0] def getitem(key): retcode1 = self.iomodule.SeekNextCase(self.fh, ctypes.c_long(int(key))) self.caseBuffer, self.caseBufferPtr = self.getCaseBuffer() retcode2 = self.iomodule.WholeCaseIn(self.fh, self.caseBufferPtr) record = struct.unpack(self.structFmt, self.caseBuffer.raw) if any([retcode1, retcode2]): raise RuntimeError, Error retrieving record %d [%s, %s] % \ (key, retcodes[retcode1], retcodes[retcode2]) return record if isinstance(key, slice): records = [getitem(i) for i in range(*key.indices(self.nCases))] return records elif hasattr(key, __int__): # isinstance(key, (int, float)): if abs(key) (self.nCases - 1): raise IndexError else: key = self.nCases + key if key 0 else key record = getitem(key) return record else: raise TypeError Another comment below: # Python 2.6.4 (r264:75708, Oct 26 2009, 08:23:19) [MSC v.1500 32 bit (Intel)] on win32 def __getitem__(self, key): This function reports the record of case numberkey. For example: firstRecord = FileReader(fileName)[0] if not isinstance(key, (int, float)): raise TypeError Floats? Do you actually have have case number (for example) 0.14285714285714285 ? For this case, I think it is reasonable to insist on exactly an int, and nothing else (except possibly a slice object, to support for example obj[2:15]). I also accepted floats as a convenience. I had examples in mind like: record = data[1.0] . Kind of annoying when this raises a TypeError. But in your example makes perfect sense to raise such an exception. Eryksun, Steven: Thanks!!! Albert-Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] (no subject)
hi to all readers, i 'm a newbie and i'm interested to learn python programming, can anybody please guide me out to learn basic to advance python programming, be actually can anyone out there should suggest a free book that i can read it on just to learn from as a newbie to python programming? i can be kindly respect and appreciate the guidance you can recommend it to me..thnx___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
