Re: [Tutor] What exactly is [::-1]?
On 26/07/07, Luke Paireepinart <[EMAIL PROTECTED]> wrote: > Wow, it was actually quite a bit harder to Google than I thought :) > well, some experimentation leads me to believe this is the syntax for > list slicing: [...] It's in the docs, albeit rather tersely: http://www.python.org/doc/current/lib/typesseq.html -- John. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] What exactly is [::-1]?
when you use the 3rd element, it's called the extended slice syntax. here are a few more examples: >>> x = 'python programming' >>> x[::-1] 'gnimmargorp nohtyp' >>> x[2:12:2] 'to rg' >>> ironically, this feature has been available in the interpreter for many years, but it wasn't until circa 2.3 that it was available via Python syntax. it was also odd that i could use the extended slice syntax with Jython (formerly JPython) 1.1 when it wasn't available in the standard C Python back in the day. hope this helps! -- wesley - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - "Core Python Programming", Prentice Hall, (c)2007,2001 http://corepython.com wesley.j.chun :: wescpy-at-gmail.com python training and technical consulting cyberweb.consulting : silicon valley, ca http://cyberwebconsulting.com ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] What exactly is [::-1]?
Dick Moores wrote: > At 08:38 PM 7/25/2007, Luke Paireepinart wrote: >> > I would like to know what exactly the index notation of [::-1] is, >> where >> > it comes from and if there are other variants. >> > >> This is called list slicing. Look into it to figure out what all this >> stuff means. >> I could send you a link but I'd just google 'python list slicing' to >> find it, so I'll leave that as an exercise for the reader. > > I don't find Google of help with this. Could someone supply a link? Wow, it was actually quite a bit harder to Google than I thought :) well, some experimentation leads me to believe this is the syntax for list slicing: x[ i : j ] slices from i to j x[ i : ] slices from i to the end of the list x[ : j ] slices from the beginning of the list to j x[ : ] slices from the beginning of the list to the unspecified parameter (the end of the list) in other words, you can use this to make a copy. x[ : : ] This seems to work the same as the above. (note that in both cases, : and ::, the list is just a one-level-deep copy. so the list [[1,2,3],[4,5,6]] can't be copied fully with this.) however, x[ : : k ] is a copy (same as above) that uses k as a step. Here are some examples that should make it make sense. >>> x = [1,2,3,4,5,6,7,8,9] >>> x[::1] [1, 2, 3, 4, 5, 6, 7, 8, 9] >>> x[::2] [1, 3, 5, 7, 9] >>> x[::5] [1, 6] >>> x[::-5] [9, 4] >>> x[::-1] [9, 8, 7, 6, 5, 4, 3, 2, 1] To summarize, the negative/positiveness of this parameter k denotes whether the step is from beginning to end, or from end to beginning. so if it's negative, the step will start at the last element, then step |k| toward the beginning, then grab that element ( if such an element exists) and proceed in this manner. This is all gleaned from experimentation, so it shouldn't be taken as the Word. HTH, -Luke > > Dick Moores > > > ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] What exactly is [::-1]?
At 08:38 PM 7/25/2007, Luke Paireepinart wrote: > > I would like to know what exactly the index notation of [::-1] is, where > > it comes from and if there are other variants. > > >This is called list slicing. Look into it to figure out what all this >stuff means. >I could send you a link but I'd just google 'python list slicing' to >find it, so I'll leave that as an exercise for the reader. I don't find Google of help with this. Could someone supply a link? Dick Moores ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Livewires questions
As promised, here's some comments on your code.
from livewires import *
begin_graphics()
allow_moveables()
def place_player():
global player_x
global player_y
global player_shape
player_y = random_between(0,47)
player_x = random_between(0,63)
player_shape = circle(10*player_x, 10*player_y, 5, filled=1)
In general, you should try to avoid global usage like this.
You'd want to have a player class, probably.
However, the way this tutorial is going, it seems like this is what it
expects you to do.
It mentions classes further near the end of the tutorial, so don't worry
about it.
for now, we'll just go with what you've got.
def place_robot():
global robot_x
global robot_y
global robot_shape
robot_y = random_between(0,47)-0.5
robot_x = random_between(0,63)-0.5
I'm not too clear why you're subtracting 0.5 here.
Doesn't this make the robot's center on the grid lines, rather than
having the robot occupy a full square on the grid?
I guess that's the intended behavior, huh?
robot_shape = box(10*robot_x, 10*robot_y,10*robot_x+10,10*robot_y+10)
def move_player():
while 1:
global player_x
global player_y
if 't' in keys:
place_player()
break
You can't reuse your place_player function here, because you put the
initialization (the creation) of the graphics that represent the player
_inside_ of the place_player function. Well, technically you could, but
it would be better instead to use move_to(player_shape, x, y) because
this doesn't overwrite the old player_shape circle.
Also, will this work if the player presses "T"?
if '8' in keys:
move_to(player_shape,player_x*10 ,player_y*10 + 10)
player_y = player_y + 1
if player_y > 47:
player_y = player_y -1
else:
pass
'if' statements don't have to have an 'else' clause.
else:
pass
is just a waste of 2 lines. 'pass' does nothing, and since the 'else'
is not required, you may as well leave it off.
break
if '7' in keys:
move_to(player_shape,player_x*10 - 10,player_y*10 +10)
player_x = player_x -1
player_y = player_y + 1
if player_x < 1 or player_y > 47:
player_x = player_x+1
player_y = player_y-1
else:
pass
break
if '9' in keys:
move_to(player_shape,player_x*10 + 10,player_y*10 + 10)
player_x = player_x +1
player_y = player_y +1
if player_x > 63 or player_y >47:
player_x = player_x -1
player_y = player_y -1
else:
pass
break
if '4' in keys:
move_to(player_shape,player_x*10 - 10,player_y*10)
player_x = player_x - 1
if player_x < 1 :
player_x = player_x+1
else:
pass
break
if '5' in keys:
break
if '6' in keys:
move_to(player_shape,player_x*10+10,player_y*10)
player_x = player_x + 1
if player_x > 63:
player_x = player_x-1
else:
pass
break
if '1' in keys:
move_to(player_shape,player_x*10-10,player_y*10-10)
player_x = player_x -1
player_y = player_y -1
if player_x < 1 or player_y < 1:
player_x = player_x +1
player_y = player_y +1
else:
pass
break
if '2' in keys:
move_to(player_shape,player_x*10,player_y*10-10)
player_y = player_y -1
if player_y < 1:
player_y = player_y+1
else:
pass
break
if '3' in keys:
move_to(player_shape,player_x*10+10,player_y*10-10)
player_x = player_x +1
player_y = player_y -1
if player_x > 63 or player_y < 1:
player_x = player_x -1
player_y = player_y +1
else:
pass
break
This big block of movement code can be shortened into a few lines.
I am not sure how much python you know, so if any of this doesn't make
sense, let me know.
Think of it this way:
step 1: look to see if they pressed a key that we want to process.
step 2: if so, figure out how we need to move the player (based on input)
step 3: check if this movement will move him out of bounds.
step 4: perform the movement.
Now that we have this pattern of evaluating our problem, we can reduce
the code.
First, what kind of data structures are we going to need?
This is how I'm going to do it:
movement = {}
for x in range(3):
for y in range(1,4):
#this goes from 0 - 9, I was just too lazy to puzzle out a more
efficient
#way to do it.
Re: [Tutor] What exactly is [::-1]?
cuell wrote: > In order to reverse the order of an array, I discovered that I'm > supposed to use [::-1]. > I don't know if 'supposed to' is the correct term. You could just as easily get away with using ['a','b','c'].reverse(). However, below you're using 'array' and I'm not sure exacly what this is. Does it have to do with the built-in array module or one of the numeric/numpy variants? > >>> a = array([1., 2., 3.]) > >>> a > array([ 1., 2., 3.]) > >>> a[::-1] > array([ 3., 2., 1.]) > >>> > > I would like to know what exactly the index notation of [::-1] is, where > it comes from and if there are other variants. > This is called list slicing. Look into it to figure out what all this stuff means. I could send you a link but I'd just google 'python list slicing' to find it, so I'll leave that as an exercise for the reader. > Thank you for your help. I lurk about on this list and have learned a > fair bit. > Good to hear :) -Luke ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] What exactly is [::-1]?
In order to reverse the order of an array, I discovered that I'm supposed to use [::-1]. >>> a = array([1., 2., 3.]) >>> a array([ 1., 2., 3.]) >>> a[::-1] array([ 3., 2., 1.]) >>> I would like to know what exactly the index notation of [::-1] is, where it comes from and if there are other variants. Thank you for your help. I lurk about on this list and have learned a fair bit. -- Charles Cuell [EMAIL PROTECTED] http://math.usask.ca/~cuell ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Livewires questions
Tonu Mikk wrote: > Thanks for offering to help! I am following the Livewires exercise > (attached file "5-robots.pdf"). I have gotten as far as page 7. > Attached is also my code so far in robotsarecoming-teleport.py. > Question 1. I was checking for collision of a robot and player first > in this way: > > def check_collisions(): >if player_x == robot_x+0.5 and player_y == robot_y+0.5: > print 'You have been caught' > > This was working fine. I then tried to create a definition like this: > > def collided(): >player_x == robot_x+0.5 and player_y == robot_y+0.5 I haven't looked at your code yet, but this doesn't seem like a very good way to check for collisions, unless the player moves on a grid of 0.5 at a time, and you guarantee that you can check if the player collided with a robot on every move. even so, doesn't this only collide with the robot if the player hits the bottom-right corner? > > and then check for collisions in this way (as in my code): > def check_collisions(): >if collided() == 1: >print 'You have been caught' The reason this isn't working is because your function 'collided' doesn't return anything. Consider this example: def foo(): "Hello" What do you expect to happen when you call foo()? 1) "Hello" won't be printed, because there is no 'print' statement here. 2) "Hello" won't be returned, because you have no return statement. So what does happen, then? well, foo() creates a string in memory with "Hello" stored in it, but there are no variables referenced to it, so nothing happens. Basically, the only thing foo() accomplishes is that it wastes memory until "Hello" is garbage collected and deleted. Now consider this: def foo(): a == b and b == c What do you expect to happen here? It's similar to the above example. a == b is evaluated. if it's true, b == c is evaluated. if it's true, then the value True is there, but it's not assigned to any variables, so it just disappears. Can you see now why your code doesn't work? Here's an example of a function you'd want to look at to give you an idea of what to do: def foo(): return a < b > But this isn't printing out anything when the player and robot > collide. I think I need to pass a variable of collided somehow, but I > am not sure how. I also tried following: > def check_collisions(): >if collided() > print 'You have been caught' > but this isn't working either. This is because collided() is not returning anything. Try this: print collided() you will get this output: None > > Question 2. I created a if statement to check if the "t" key is > pressed on a keyboard. If it is, I want the player to be placed on > another location on the grid. However nothing happens when I press > the "t" key. I am not sure why. Instead of changing the player's location, print "YOU PRESSED T" instead, and if you see that in the console, you know there's a problem with your repositioning code. If you don't see that, you know it's a problem with your input code. If you can't diagnose further than that, let us know. > > Question 3. I think there is something strange about how I check that > my player is within the boundaries of the grid. When it gets close to > the edges of the grid, it can sometimes disappear past it even though > I thought I had prevented this from happening. It's probably similar to the thing I was mentioning above. Imagine that you have this case: you're checking if the player is hitting 0.5, 0.5 now if the player can move by acceleration, etc... and you can't guarantee that it moves exactly in .5 increments, the player may very well move to the position .51,.51 and from there, to .49, .49 which would negate your test. Even if you check a range of values (for example, 0.0 - 0.5 in the x axis and 0.0 - 0.5 in the y axis) the player could theoretically jump right over this boundary (unless you restrict his maximum movement speed.) The best way to check would be: Say you have the player's coordinates playerx, playery and your player-permitted space is 0,0 to 1024, 768 I would suggest something like this: newx, newy = (playerx + movex, playery + movey) if newx >= 0 and newx < 1024: playerx = newx if newy >= 0 and newy < 768: playery = newy This will only allow the player to move to wherever he's moving IFF he's not moving out of bounds. Otherwise, he just stays where he is. Alternatively, you could check the boundaries, and if he's outside, set him to the boundary. That way you could have the player walk right up to the wall, which isn't allowed in my code (depending how fast the player moves) For example, if the player moves at 1.5, and he's at the position 1.4, he won't be able to move any closer to the wall. > > > Thank you again for looking at this. The attached bit of code has > taken a long time to create. I admire all who can program :-). Hey, I'm going to send this e-mail now, so everyone on the list (you included) will be able to rea
Re: [Tutor] How to determine if every character in one string is inanother string?
Alan Gauld wrote: > "Terry Carroll" <[EMAIL PROTECTED]> wrote > >> if Y in X: > > FWIW I believe that 'in' did only work for single characters up until > version 2.X so your ideas may have been based on experiences with > an earlier Python version. Yes, it changed in Python 2.3. Kent ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Livewires Python course
Kent Johnson wrote: > Tonu Mikk wrote: > >> I also >> began reading and coding the Livewires course exercises >> (http://www.livewires.org.uk/python/). I have gotten through the first >> 4 exercise, but got stuck with the last one where we build a robot >> game. The Livewires coding exercise uses modules that can be downloaded >> from their website. Would anyone be willing to install Livewires >> modules on their computer and assist me with the coding? I have >> specific questions, but the code could be difficult to read because it >> takes advantage of the imported modules. >> > > Go ahead and post your questions. I have tried LiveWires (long ago!) and > there may be others on the list. > Yes, but please next time you start a thread don't do it as a reply to another thread. My e-mail client threw your e-mail in with the 'function declaration problems' thread, which, if I had decided I didn't need to watch that thread anymore, would've resulted in your question getting overlooked. So overall your questions get less exposure that way, as well as breaking the threading of some mail clients. Let us know what specific questions you have. -Luke ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] How to determine if every character in one string is inanother string?
"Terry Carroll" <[EMAIL PROTECTED]> wrote > if Y in X: > > Which is much more elegant/pythonic; but I didn't know you could do > that > with one string over another. For some reason, I had thought Y > would have > to exactly match one iterable element in X (e.g., one element of a > list, > or one character of a string) for that to work. FWIW I believe that 'in' did only work for single characters up until version 2.X so your ideas may have been based on experiences with an earlier Python version. Alan G. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] How to determine if every character in one string is inanother string?
On Tue, 24 Jul 2007, wesley chun wrote: > i don't have any time myself either (getting ready for OSCON talk), > but i'm not sure what terry's OP was about... looking for a > well-written piece of code, a faster-performing snippet, or both? i > think he was just unsatissfied with his 1st attempt. Exactly. It worked fine, but just seemed unpythonic to me. To use an analogy, not long ago I thought the best way to see if string X contained string Y was: if X.find(Y) != -1 Which works just fine. But another poster pointed out: if Y in X: Which is much more elegant/pythonic; but I didn't know you could do that with one string over another. For some reason, I had thought Y would have to exactly match one iterable element in X (e.g., one element of a list, or one character of a string) for that to work. Similarly, I was thinking that while that first attempt of mine worked, its apparent-to-me lameness suggested that there was a more idiomatic approach, and I wanted to find out what that was. Seeing the different approaches put forward by the various contributors was pretty interesting, though, I must say. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] function declaration problems perhaps?
> By the way, this is an important and fundamental subject about > Python. When I teach classes on Python, I always need to explain > Python's execution model, and I always struggle with it. So, > anything you can tell me that would help me teach this will be much > appreciated. > > Dave The way I keep it clear is simple. If python needs the value of the name (it has to look it up) then it had better be defined. Otherwise ~ It doesn't matter! Think of it like assignment. x = 1 Does python need to know the current value of x? No. Then x does not have to be previously defined. f() Does python need to know the current value of f? Yes. It has to know that f is a function, and where the address is, etc. def f1(): f() Does python need to know the current value of f? No. Not until f1 is executed. Does this help? Only one rule to remember. ;-) ~Does python need to know the value of _this_ variable?~ JS ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Livewires Python course
Tonu Mikk wrote: > I also > began reading and coding the Livewires course exercises > (http://www.livewires.org.uk/python/). I have gotten through the first > 4 exercise, but got stuck with the last one where we build a robot > game. The Livewires coding exercise uses modules that can be downloaded > from their website. Would anyone be willing to install Livewires > modules on their computer and assist me with the coding? I have > specific questions, but the code could be difficult to read because it > takes advantage of the imported modules. Go ahead and post your questions. I have tried LiveWires (long ago!) and there may be others on the list. Kent ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] Livewires Python course
Hello, I am at a very beginning on trying to learn Python. So far I have read first few chapters of Alan Gauld tutorials, and completed all the exercises of Guido van Robot (http://gvr.sourceforge.net/). I also began reading and coding the Livewires course exercises (http://www.livewires.org.uk/python/). I have gotten through the first 4 exercise, but got stuck with the last one where we build a robot game. The Livewires coding exercise uses modules that can be downloaded from their website. Would anyone be willing to install Livewires modules on their computer and assist me with the coding? I have specific questions, but the code could be difficult to read because it takes advantage of the imported modules. Thank you, Tonu ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Logging module
> I found the problem. It was rather simple actually. I didn't have remote > logging enabled for syslog. Even though I was logging to localhost, for > some reason, it wouldn't work until I gave syslogd a -r at startup. > Thanks localhost is still remote, in that sockets are used to reach it. The implementation doesn't know the difference between 127.0.0.1 and 241.12.31.7 because it's easier than making a special case. JS ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Text matching and replacing
> Cheers for the critique I'll take you points on board .especially
> this schoolboy error
It's not an error, really. It will work. Just... not intuitive
Errors are things that do not work.
> One thing to note about the re expression is that the products are not
> these were just substitutes. In reality these are product
> names with no commonality e.g. ('baked beans'|'tuna'|'salad')
>
> So with that in mind is the way I have set the re way the best way or is
> there an another more pythonic way.
I can't tell you one way or the other, (and I have a hard time determining
that which makes something more or less pythonic) but i have noticed that
using re expressions for fixed patterns like that (no special identifiers,
etc.) is considered overkill. It is easier to use string methods.
> As an aside I don't believe there were any tips in there to help solve
> the problems I have...again any help would be warmly appreciated.
However, the answer to your problem may be that you could rely on re
expressions more than you are. What I like about regular expressions is the
sheer power. Watch.
import re
teststring = """
Name: Jacob Schmidt
Address: 1234 Fake Street
City: Nowhere
State: Indiana
Zip Code: 14241
Name: Tiger Power
Address: 4321 Mysterious Lane
City: Jersey
State: Indiana
Zip Code: 14051-1390
"""
pat = re.compile(r".*Name: (.*)\nAddress: (.*)\nCity: (.*)\nState: (.*)\nZip
Code: (\d{5}(?:-\d{4})?).*")
lst = pat.findall(teststring)
for x in lst:
print x
##
I'm sure this will help you some. :-)
JS
___
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Re: [Tutor] function declaration problems perhaps?
Alan Gauld wrote: > "Kent Johnson" <[EMAIL PROTECTED]> wrote > > >>> Perl executes differently to Python in that it does a compilation >>> stage before executing. Therefore Perl knows about all the function >>> definitions prior to executing any code. Python compiles modules >>> which it imports >>> but not scripts which it executes. >>> >> Python compiles all scripts to bytecode. >> > > Doh! Yes of course it does, stoopid me. > > >> scripts. However this has no bearing on the current thread; for both >> imported modules and executed scripts, a function must be defined >> before >> it can be called. >> > > Yes, the bearing is in the way that Perl compiles its code. > Perl builds a name tree from the entire file before executing > so it doesn't rely on the order of definition, Python seems > to compile and execute code in a sequential manner and > therefore relies on the sequence being right. > > I'm not sure if the undefined name errors come from the compilation > or from the execution - does anyone else. I confess i've never looked > deeply into how Python actually does its complile/execute cycle. > Compiling to bytecode raises syntax, deprecation and indentation errors. All others AKAIK are raised during execution > Alan G. > > > ___ > Tutor maillist - Tutor@python.org > http://mail.python.org/mailman/listinfo/tutor > > -- Bob Gailer 510-978-4454 Oakland, CA 919-636-4239 Chapel Hill, NC ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] function declaration problems perhaps?
On Wed, Jul 25, 2007 at 06:21:08PM +0100, Alan Gauld wrote: > > I'm not sure if the undefined name errors come from the compilation > or from the execution - does anyone else. I confess i've never looked > deeply into how Python actually does its complile/execute cycle. > A couple of points that might help: 1. In python it's all execution. Yes, Kent is right that Python is compiled to byte code. But, Alan is right to ignore that in trying to understand what happens. In particular, "class" and "def" statements execute, and when they do they bind a name to a class or function object in the local namespace. 2. It's all about look-up. Every variable reference causes Python to do a look-up in the current namespace (and enclosing namespaces, which is another subject). So, you need to ask whether at that time a given name has been created in the current namespace. Some examples ... The following works because func2 is not called (looked up) until func1 is executed, which is after func2 is defined: # Test 1 def func1(): func2() def func2(): print 'hello' func1() The following does *not* work, because func1 executes *before* func2 is defined, which means that func2 is needed before it is defined: # Test 2 def func1(): func2() func1() def func2(): print 'hello' And, (admittedly a rare case), the following does *not* work because when the statement "class A(B)" executes, B is not yet defined and is needed. This is an example of a name (B) being needed when another object (A) is defined (when the "class A(B)" is executed): # Test 3 class A(B): pass class B(object): pass By the way, this is an important and fundamental subject about Python. When I teach classes on Python, I always need to explain Python's execution model, and I always struggle with it. So, anything you can tell me that would help me teach this will be much appreciated. Dave -- Dave Kuhlman http://www.rexx.com/~dkuhlman ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] function declaration problems perhaps?
Alan Gauld wrote: > "Kent Johnson" <[EMAIL PROTECTED]> wrote >> scripts. However this has no bearing on the current thread; for both >> imported modules and executed scripts, a function must be defined >> before >> it can be called. > > Yes, the bearing is in the way that Perl compiles its code. > Perl builds a name tree from the entire file before executing > so it doesn't rely on the order of definition, Python seems > to compile and execute code in a sequential manner and > therefore relies on the sequence being right. It executes code in a sequential manner, and names are bound during execution, not compilation. That is the key difference. I guess you could say that the compiler doesn't forward any names to the execution phase; when a module starts executing, the only names in the module namespace are ['__builtins__', '__doc__', '__file__', '__name__'] You can see this if you import a module whose contents are just print dir() Any other names must be bound by executing code. > I'm not sure if the undefined name errors come from the compilation > or from the execution - does anyone else. I confess i've never looked > deeply into how Python actually does its complile/execute cycle. They come from execution. See my separate post about def, etc. being executable statements. Kent ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] function declaration problems perhaps?
"Kent Johnson" <[EMAIL PROTECTED]> wrote >> Perl executes differently to Python in that it does a compilation >> stage before executing. Therefore Perl knows about all the function >> definitions prior to executing any code. Python compiles modules >> which it imports >> but not scripts which it executes. > > Python compiles all scripts to bytecode. Doh! Yes of course it does, stoopid me. > scripts. However this has no bearing on the current thread; for both > imported modules and executed scripts, a function must be defined > before > it can be called. Yes, the bearing is in the way that Perl compiles its code. Perl builds a name tree from the entire file before executing so it doesn't rely on the order of definition, Python seems to compile and execute code in a sequential manner and therefore relies on the sequence being right. I'm not sure if the undefined name errors come from the compilation or from the execution - does anyone else. I confess i've never looked deeply into how Python actually does its complile/execute cycle. Alan G. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] function declaration problems perhaps?
Alan Gauld wrote:
> "nibudh" <[EMAIL PROTECTED]> wrote
>
>
>> in perl this works:
>>
>> #!/usr/bin/env perl
>> hello("World");
>>
>> sub hello {
>>print "Hello ". $_[0] . "\n";
>> }
>>
>
>
> Perl executes differently to Python in that it does a compilation
> stage
> before executing. Therefore Perl knows about all the function
> definitions
> prior to executing any code. Python compiles modules which it imports
> but not scripts which it executes.
>
Not exactly. When Python imports a module that is new* it "compiles" it
into bytecode. No recognition of names or objects takes place in this
step. The bytecode is saved in a file with extension .pyc. Then Python
executes the bytecode. Any function definitions that get executed create
function objects that are available to subsequently executed code.
Running a script does exactly the same thing, except the bytecode is not
saved in a file.
The bottom line is: a function definition must be executed before the
function can be used. This is true of ANY Python object.
*new means that no .pyc file exists or the modification time of the .py
is more recent than that of the .pyc.
>
>> I have a vague recollection that ASP works in a similar way to
>> python hence
>> the "hunch" i had earlier but i could be wrong. It's been a while
>> since i've
>> done programming.
>>
>
> Most interpreted languages work this way.
> Even the original versions of C worked that way although I thiunk more
> recent (ANSI/ISO compliant?) versions no longer need the strict
> ordering,
> and Pascal also does it that way even though they are pure compiled
> languages. In the case of Pascal it is because Pascal is designed to
> be a single pass comilation language - which is why Borland's Object
> Pascal comiles so quickly in Delphi!
>
>
--
Bob Gailer
510-978-4454 Oakland, CA
919-636-4239 Chapel Hill, NC
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Re: [Tutor] function declaration problems perhaps?
Alan Gauld wrote:
> "nibudh" <[EMAIL PROTECTED]> wrote
>
>> in perl this works:
>>
>> #!/usr/bin/env perl
>> hello("World");
>>
>> sub hello {
>>print "Hello ". $_[0] . "\n";
>> }
>
>
> Perl executes differently to Python in that it does a compilation
> stage
> before executing. Therefore Perl knows about all the function
> definitions
> prior to executing any code. Python compiles modules which it imports
> but not scripts which it executes.
Python compiles all scripts to bytecode. For imported modules it saves
the compiled bytecode in a .pyc file, but not for directly-executed
scripts. However this has no bearing on the current thread; for both
imported modules and executed scripts, a function must be defined before
it can be called.
Kent
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Re: [Tutor] Logging module
Thanks for the reply Kent.
I found the problem. It was rather simple actually. I didn't have remote
logging enabled for syslog. Even though I was logging to localhost, for
some reason, it wouldn't work until I gave syslogd a -r at startup. Thanks
jay
On 7/25/07, Kent Johnson <[EMAIL PROTECTED]> wrote:
jay wrote:
> Hello,
>
> I'm trying to setup simple Syslog logging in python using the logging
> module. I would like to use a config file, but so far haven't been able
> to get the correct configuration. Actually, I don't get any warnings or
> errors, program runs fine, but nothing is logged anywhere. I have my
> syslog LOCAL6 setup to go to /var/log/scripts.log, and that worked fine
> during testing of the syslog module. But logging gives me more
> flexibility, I'd rather use that.
>
> Anyone with some experience using this module? The documentation, at
> least to me, is a bit confusing, and I haven't found a good example on
> the web yet.
I haven't used logging config files, but I don't see anything obviously
wrong here. A couple of ideas to try:
- make sure logging.conf can be found by
print os.path.exists('logging.conf')
- turn on console logging in the config file and see if that works
- try to configure the syslog handler in code instead of in a file, then
translate the successful configuration to a file.
Kent
>
> ---main.py---
> #!/usr/bin/env python
>
> import logging, logging.config
>
> logging.config.fileConfig('logging.conf')
>
> log = logging.getLogger()
> log.info('here we go, testing logger')
> --- end main.py ---
>
> --- logging.conf ---
> [formatters]
> keys: detailed,simple
>
> [handlers]
> keys: console,syslog
>
> [loggers]
> keys: root
>
> [formatter_simple]
> format: %(name)s:%(levelname)s: %(message)s
>
> [formatter_detailed]
> format: %(name)s:%(levelname)s %(module)s:%(lineno)d: %(message)s
>
> [handler_console]
> class: StreamHandler
> args: []
> formatter: simple
>
> [handler_syslog]
> class: handlers.SysLogHandler
> args: [('localhost', handlers.SYSLOG_UDP_PORT),
> handlers.SysLogHandler.LOG_LOCAL6 ]
> formatter: detailed
>
> [logger_root]
> level: INFO
> handlers: syslog
>
> end logging.conf ---
>
> Thanks for any help!
>
> jay
>
>
>
>
> ___
> Tutor maillist - Tutor@python.org
> http://mail.python.org/mailman/listinfo/tutor
___
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Re: [Tutor] function declaration problems perhaps?
"nibudh" <[EMAIL PROTECTED]> wrote
> in perl this works:
>
> #!/usr/bin/env perl
> hello("World");
>
> sub hello {
>print "Hello ". $_[0] . "\n";
> }
Perl executes differently to Python in that it does a compilation
stage
before executing. Therefore Perl knows about all the function
definitions
prior to executing any code. Python compiles modules which it imports
but not scripts which it executes.
> I have a vague recollection that ASP works in a similar way to
> python hence
> the "hunch" i had earlier but i could be wrong. It's been a while
> since i've
> done programming.
Most interpreted languages work this way.
Even the original versions of C worked that way although I thiunk more
recent (ANSI/ISO compliant?) versions no longer need the strict
ordering,
and Pascal also does it that way even though they are pure compiled
languages. In the case of Pascal it is because Pascal is designed to
be a single pass comilation language - which is why Borland's Object
Pascal comiles so quickly in Delphi!
--
Alan Gauld
Author of the Learn to Program web site
http://www.freenetpages.co.uk/hp/alan.gauld
___
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Re: [Tutor] comparing lists, __lt__ and __gt__
Andrew Purdea wrote: > Hello! > I can see that lists have implemented these methods in jython.. > But i can not find any documentation on this. It looks like python > compares each element, and and when it finds a difference, it returns. > Where can i find documenation on this? Will this behaviour remain in > python for future releases? Good question! The only doc I can find on this behavior is this: http://docs.python.org/lib/comparisons.html which just says that the comparison operation exists. There doesn't seem to be any documentation on how comparison works with sequences. I think it is pretty safe to count on the current behaviour of < and > for lists. I'll put in a documentation bug on this - the meaning of these operations (and ==) should be explicit in the docs. Kent ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] comparing lists, __lt__ and __gt__
Andrew Purdea wrote: > Hello! > I can see that lists have implemented these methods in jython.. > But i can not find any documentation on this. It looks like python > compares each element, and and when it finds a difference, it returns. > Where can i find documenation on this? In python 2.5 reference 3.4.1: *__lt__*( self, other) *__le__*( self, other) *__eq__*( self, other) *__ne__*( self, other) *__gt__*( self, other) *__ge__*( self, other) New in version 2.1. These are the so-called ``rich comparison'' methods, and are called for comparison operators in preference to __cmp__() below. The correspondence between operator symbols and method names is as follows: |xy| call |x.__ne__(y)|, |x>y| calls |x.__gt__(y)|, and |x>=y| calls |x.__ge__(y)|. These methods can return any value, but if the comparison operator is used in a Boolean context, the return value should be interpretable as a Boolean value, else a TypeError will be raised. By convention, |False| is used for false and |True| for true. There are no implied relationships among the comparison operators. The truth of |x==y| does not imply that |x!=y| is false. Accordingly, when defining __eq__(), one should also define __ne__() so that the operators will behave as expected. There are no reflected (swapped-argument) versions of these methods (to be used when the left argument does not support the operation but the right argument does); rather, __lt__() and __gt__() are each other's reflection, __le__() and __ge__() are each other's reflection, and __eq__() and __ne__() are their own reflection. Arguments to rich comparison methods are never coerced. A rich comparison method may return |NotImplemented| if it does not implement the operation for a given pair of arguments. > Will this behaviour remain in python for future releases? I certainly hope so. A LOT of programs would suffer if not. I certainly have not seen any PEPs that discuss replacing or eliminating these. -- Bob Gailer 510-978-4454 Oakland, CA 919-636-4239 Chapel Hill, NC ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] location of points in a covariance matrix
Beanan O Loughlin wrote: > Hi all, I'm a meteorology postgrad working with python for the first time. > > I have found the location minimum in a large covariance matrix. this > value corresponds to the covariance of two points on a latitude, > longitude grid. > > I need to find a method to locate these two points on the lat,lon grid. Usually multi-dimensional arrays are stored in "row-major" order. So the subscripts of an array of shape 2,3,4 (planes, rows. columns) would look like: 1,1,1 1,1,2 1,1,3 1,1 4 1,2,1 1,2,2 1,2,3 1,2,4 1,3,1 1,3,2 1,3,3 1,3,4 2,1,1 2,1,2 2,1,3 2,1 4 2,2,1 2,2,2 2,2,3 2,2,4 2,3,1 2,3,2 2,3,3 2,3,4 When you reshape it to 2,12 the elements remain "in place", and the subscripts now are: 1,1 1,2 1,3 1,4 1,5 1,6 1,7 1,8 1,9 1,10 1,11 1,12 2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8 2,9 2,10 2,11 2,12 Is that enough of a hint? > > this is the code i have used, where 'se' is a 3-D array of data > > > >>> nt,nlat,nlon = shape(se) > >>>nt,nlat,nlon# 3-D array of data taken > 1464 times, over 41 latitudes and 58 longitudes > (1464, 41, 58) > >>> > >>> > >>>m=reshape(se,(nt,nlat*nlon))# reshape to (time,latitude > longitude data point) where 2378 = 41*58 > >>> > >>>shape(m) > (1464,2378) > >>> > >>> > >>>covmat=cov(m) # calculate covariance matrix > >>> > >>>shape(covmat) > (2378,2378) > > >>>def min(R): >U = triu(R) #just use one half of > the diagonal matrix >n = U.shape[0] >U.flat[::n+1] = 10.0#give the diagonal elements a > large value so they wont be selected >k = argmin(U.flat)#find the min value of > the flattened array >i, j = divmod(k,n) #calculate the index of > the minimum data >return i, j, R[i,j] > > >>> > >>> min(covmat) > (7, 1914, -2.3016361721151051) > > so the minimum is found at (7,1914) in the covariance matrix and has a > value of - 2.3 > > This min point corresponds to the covariance between two 'lat,lon' > data points in my (41,58) sample grid. > > Is there a way i can move back from my (2378,2378) covariance matrix > to see where these two points are located on the (41, 58) grid? > > Thank you very much in advance > > B. > > > > ___ > Tutor maillist - Tutor@python.org > http://mail.python.org/mailman/listinfo/tutor > -- Bob Gailer 510-978-4454 Oakland, CA 919-636-4239 Chapel Hill, NC ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] function declaration problems perhaps?
Hi Kent and Alan,
Thanks for the responses. It really got me thinking!
To test what i thought i knew, i wrote a "hello world" script in perl and
python.
in perl this works:
#!/usr/bin/env perl
hello("World");
sub hello {
print "Hello ". $_[0] . "\n";
}
but in python:
#!/usr/bin/env python
hello('World')
def hello(name):
print "Hello" + name
That doesn't.
I have a vague recollection that ASP works in a similar way to python hence
the "hunch" i had earlier but i could be wrong. It's been a while since i've
done programming.
I can see how the property of being executable (defs and imports) could be
handy, but right now I'm still getting to grips with the language proper.
Thanks again for the explanations and I'll keep them in mind as i experiment
some more with python.
nibudh.
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Re: [Tutor] Text matching and replacing
Cheers for the critique I'll take you points on board .especially
this schoolboy error
def findTestDirectories(path):
os.chdir(path)
directory_listing = os.listdir(os.getcwd())
--
Change this to
directory_listing = os.listdir(path)
Why look up the current directory when you have *just* set what it is?
One thing to note about the re expression is that the products are not
these were just substitutes. In reality these are product
names with no commonality e.g. ('baked beans'|'tuna'|'salad')
So with that in mind is the way I have set the re way the best way or is
there an another more pythonic way.
As an aside I don't believe there were any tips in there to help solve
the problems I have...again any help would be warmly appreciated.
Cheers
Dean
Message: 3
Date: Tue, 24 Jul 2007 14:18:46 -0500
From: "Tiger12506" <[EMAIL PROTECTED]>
Subject: Re: [Tutor] Text matching and replacing
To:
Message-ID: <[EMAIL PROTECTED]>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
reply-type=original
def findTestDirectories(path):
os.chdir(path)
directory_listing = os.listdir(os.getcwd())
--
Change this to
directory_listing = os.listdir(path)
Why look up the current directory when you have *just* set what it is?
test_record_directories = []
for directory in directory_listing:
if "TestRecords" in directory:
test_record_directories.append(directory)
--
This whole block could be turned into a list comprehension
test_record directories = [di for di in directory_listing if
"TestRecords"
in di]
-
return test_record_directories
def findProductFromComments(records_from_record_file):
'''
Attempt to find products run against in the comment field
if we find one. Write it to the newly created product run field
'''
searchText = re.compile(r'(|||)', re.IGNORECASE)
---
Woah! Regular expression could use work.
Try:
re.compile(r'', re.IGNORECASE)
This will match product #s 1-9
If you want to match all product numbers to infinity put a * after \d
--
for record in records_from_record_file:
if searchText.findall(record) !=[]:
---
if searchText.findall(record):
is sufficient
-
print record.split("\n\n")
def amendProductField(dir):
fileList = os.listdir(dir)
currPath = os.getcwd()+"\\"+dir+"\\"
This could be
currPath = os.path.join(os.getcwd(), dir)
--
dict_of_amended_records = {}
list_of_amended_records = []
for file in fileList:
if "CVS" in file:
pass
else:
f = open(currPath+"\\"+file)
---
And again ~
f = open(os.path.join(currPath,file))
--
if debug:
print "opening %s for reading" %file
fileContents = f.read()
fileContents = fileContents.split("\n\n")
findProductFromComments(fileContents)
for record in fileContents:
record+="\nProductRun:\n\n"
list_of_amended_records.append(record)
dict_of_amended_records[file] = list_of_amended_records
list_of_amended_records = []
#writeUpdatedRecordsToFile(currPath,dict_of_amended_records)
test_dir = findTestDirectories("C:\\Sandbox")
if debug:
print "Opening %s for amending" %test_dir[0]
#for directory in test_dir:
#amendProductField(directory)
amendProductField(test_dir[0])
Current Record:
TestedDate: 2005-04-30
TestId: 001591
Branch:
Version: 3351
SpecId: Specification--0966
Cpu: Pentium 4
OperatingSystem: Windows 2000
CpuCount: Single
Tester: someone
Comment: Run on
MinutesTaken: 5
PassOrFail: Pass
Desired Record:
TestedDate: 2005-04-30
TestId: 001591
Branch:
Version: 3351
SpecId: Specification--0966
Cpu: Pentium 4
OperatingSystem: Windows 2000
CpuCount: Single
Tester: someone
Comment: Run on
MinutesTaken: 5
PassOrFail: Pass
Product:
Dean Gardner
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Re: [Tutor] Logging module
jay wrote:
> Hello,
>
> I'm trying to setup simple Syslog logging in python using the logging
> module. I would like to use a config file, but so far haven't been able
> to get the correct configuration. Actually, I don't get any warnings or
> errors, program runs fine, but nothing is logged anywhere. I have my
> syslog LOCAL6 setup to go to /var/log/scripts.log, and that worked fine
> during testing of the syslog module. But logging gives me more
> flexibility, I'd rather use that.
>
> Anyone with some experience using this module? The documentation, at
> least to me, is a bit confusing, and I haven't found a good example on
> the web yet.
I haven't used logging config files, but I don't see anything obviously
wrong here. A couple of ideas to try:
- make sure logging.conf can be found by
print os.path.exists('logging.conf')
- turn on console logging in the config file and see if that works
- try to configure the syslog handler in code instead of in a file, then
translate the successful configuration to a file.
Kent
>
> ---main.py---
> #!/usr/bin/env python
>
> import logging, logging.config
>
> logging.config.fileConfig('logging.conf')
>
> log = logging.getLogger()
> log.info('here we go, testing logger')
> --- end main.py ---
>
> --- logging.conf ---
> [formatters]
> keys: detailed,simple
>
> [handlers]
> keys: console,syslog
>
> [loggers]
> keys: root
>
> [formatter_simple]
> format: %(name)s:%(levelname)s: %(message)s
>
> [formatter_detailed]
> format: %(name)s:%(levelname)s %(module)s:%(lineno)d: %(message)s
>
> [handler_console]
> class: StreamHandler
> args: []
> formatter: simple
>
> [handler_syslog]
> class: handlers.SysLogHandler
> args: [('localhost', handlers.SYSLOG_UDP_PORT),
> handlers.SysLogHandler.LOG_LOCAL6 ]
> formatter: detailed
>
> [logger_root]
> level: INFO
> handlers: syslog
>
> end logging.conf ---
>
> Thanks for any help!
>
> jay
>
>
>
>
> ___
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___
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Re: [Tutor] function declaration problems perhaps?
Alan Gauld wrote:
> "nibudh" <[EMAIL PROTECTED]> wrote
>
>> I looked over my code (all 41 lines!) and couldn't find anything,
>> then on a
>> hunch i moved the def statement _above_ the rest of my code and hey
>> presto
>> it worked.
>>
>> I vaguely understand why this is happening, but can someone explain
>> it to
>> me.
>
> Its pretty simple.
> Python processes the file top to bottom. If it comes upon
> a name that it doesn't recofgnise it generates an error.
A key concept to understand is that def (and class and import) are
executable statements that have no effect until they are actually
executed. The effect of executing a def is to create a function object
and bind it to the name given in the def. Before the def is executed,
the name is not bound to anything and can't be used.
This is a shift from less-dynamic languages such as Java and C, where
functions exist from the time a module is loaded.
One consequence of executable def is that you can, for example, have
conditional defs:
if has_foo:
def bar():
# Implementation of bar using foo
else:
def bar():
# Implementation of bar without using foo
Similar techniques can be used with imports. This can be handy for
writing code that is backwards compatible. For example here is some code
that tries to import ElementTree from its Python 2.5 library package and
from the effbot distribution:
try:
import xml.etree.ElementTree as ET # in python >=2.5
except ImportError:
try:
import elementtree.ElementTree as ET # effbot's pure Python module
except ImportError:
raise ImportError("Can't import ElementTree")
If this code successfully executes, the ElementTree module will be
available as ET.
Kent
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[Tutor] comparing lists, __lt__ and __gt__
Hello! I can see that lists have implemented these methods in jython.. But i can not find any documentation on this. It looks like python compares each element, and and when it finds a difference, it returns. Where can i find documenation on this? Will this behaviour remain in python for future releases? Thanks Regards, Andrew ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] function declaration problems perhaps?
"nibudh" <[EMAIL PROTECTED]> wrote > I looked over my code (all 41 lines!) and couldn't find anything, > then on a > hunch i moved the def statement _above_ the rest of my code and hey > presto > it worked. > > I vaguely understand why this is happening, but can someone explain > it to > me. Its pretty simple. Python processes the file top to bottom. If it comes upon a name that it doesn't recofgnise it generates an error. Thus: # print foo(42) def foo(x): return x * 2 ## will generate an error because at the point where the print statement tries to execute foo(42), foo does not exist! This is one good reason to avoid putting executable code in the main body of a file but to always wrap it in a function like so: ## def main() print foo(42) def foo(x): return x * 2 if __name__ == "__main__": main() ### Now the code doesn't get executed until the last line of the file by which time all definitions have been executed and the program will work correctly. This also makes the module inherently more reusable since it can be imported without the main code being executed (the purpose of the if expression.) HTH, -- Alan Gauld Author of the Learn to Program web site http://www.freenetpages.co.uk/hp/alan.gauld ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] function declaration problems perhaps?
Hi list, I've just been writing a small script to parse some xml files and output tab separated values into a separate file. I was surprised to see that my function "processXML(fpart)" was failing with an error along the lines of "processXML not defined" I looked over my code (all 41 lines!) and couldn't find anything, then on a hunch i moved the def statement _above_ the rest of my code and hey presto it worked. I vaguely understand why this is happening, but can someone explain it to me. If this makes no sense then tell me that too :-) cheers, nibudh. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
