Python information and short questions megathread.

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No Safe Word: Feb 26, 2005

JoeNotCharles posted:

Fixed your variable name for you.

l = list("1234") is easier and clearer.

Argh, don't do this either :p (I'm sounding like the crotchety old man in this thread). If you want to use a single-letter variable name for a list, use L instead of l. l is a bad variable name in any language because it looks too much like 1 in fixed-width fonts.

# ? Apr 3, 2008 15:49

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# ? Apr 28, 2024 05:20

hey mom its 420: May 12, 2007

lst

# ? Apr 3, 2008 16:39

deimos: Nov 30, 2006; Forget it man this bat is whack, it's got poobrain!

No Safe Word posted:

Argh, don't do this either :p (I'm sounding like the crotchety old man in this thread). If you want to use a single-letter variable name for a list, use L instead of l. l is a bad variable name in any language because it looks too much like 1 in fixed-width fonts.

Not if you're using a good coding font. Fonts should not affect how you code.

# ? Apr 3, 2008 18:35

bitprophet: Jul 22, 2004; Taco Defender

deimos posted:

Not if you're using a good coding font. Fonts should not affect how you code.

Except for the myriad of places that code is seen outside of your preferred editor, such as on pastebin websites. It's silly to do things (or rather, to not do them) which require a particular editor/font choice/keyboard layout/etc, when it's just as easy to do the right thing which won't break everywhere else.

# ? Apr 3, 2008 20:57

Habnabit: Dec 30, 2007; lift your skinny fists like
antennas in germany.

deimos posted:

Not if you're using a good coding font. Fonts should not affect how you code.

PEP 8 posted:

Prescriptive: Naming Conventions

Names to Avoid

Never use the characters `l' (lowercase letter el), `O' (uppercase
letter oh), or `I' (uppercase letter eye) as single character variable
names.

In some fonts, these characters are indistinguishable from the numerals
one and zero. When tempted to use `l', use `L' instead.

# ? Apr 4, 2008 03:38

tehk: Mar 10, 2006; [-4] Flaw: Heart Broken - Tehk is extremely lonely. The Gay Empire's ultimate weapon finds it hard to have time for love.

I think the only time I had an issue with 'l' was when I committed some code to a project with a fairly strict(for a python project) coding style and I broke some naming conventions by naming a method(that required a L/l as its first letter) with a uppercase L to avoid misreading. Someone submitted a 'fix' later that day.

# ? Apr 4, 2008 11:01

chutwig: May 28, 2001; BURLAP SATCHEL OF CRACKERJACKS

Is the smtplib module not thread-safe or something? I have a little monitor script set up to monitor some SQL servers and send out an e-mail if there's a long-running query that's taking up too much time on the server. Everything works fine, but when I added smtplib into the mix, everything went all wrong. As soon as the monitor thread sends an e-mail, the script just seems to stop execution shortly after the server.quit(). It sends that e-mail fine (with some formatting issues, but I'll fix that poo poo later) and I see all the debug output on the terminal from set_debuglevel(), and I see it print "E-mail successful" as well (because I added that after the server.quit() to see if it was hanging on waiting for the connection to time out or something), but it never exits the enclosing elif. It's not using any CPU time or anything... it just doesn't do anything. Here's the relevant code:

code:

for k in new_current_pid_dict:
    if new_current_pid_dict[k][2]:
        pass
    elif (new_current_pid_dict[k][1] - new_current_pid_dict[k][0]) > 15: #3h
        from_addr = "pgmonitor@blah"
        to_addr = "me@blah"
        subject = "Database process",k
        warning_text = "Database process",k,"has been running for more than three hours.\r\n \
        Please review this process and terminate it if necessary with 'kill -SIGINT",k,"."
        msg = "From: %s\r\nTo: %s\r\nSubject: %s\r\n\r\n%s" % (from_addr,to_addr,subject,warning_text)

        print "SENDING EMAIL",k
        server = smtplib.SMTP('localhost')
        server.set_debuglevel(1)
        server.sendmail(from_addr,to_addr,msg)
        server.quit()
        print "E-mail successful"
        new_current_pid_dict[k][2] = True

If I just have it print a string or something, no problem, the script continues as normal. smtplib's presence here is loving things up in some way.

# ? Apr 9, 2008 16:27

m0nk3yz: Mar 13, 2002; Behold the power of cheese!

Chutwig Regarding smtplib - did you look at this thread on c.l.p?

http://groups.google.com/group/comp...a1de3ed29133546

# ? Apr 9, 2008 20:49

chutwig: May 28, 2001; BURLAP SATCHEL OF CRACKERJACKS

m0nk3yz posted:

Chutwig Regarding smtplib - did you look at this thread on c.l.p?

http://groups.google.com/group/comp...a1de3ed29133546

After I posted, I went back and googled some more and found that discussion. I'll probably just write another script external to this one to handle e-mailing and invoke it through subprocess, or just invoke sendmail directly, or something.

# ? Apr 9, 2008 21:09

ashgromnies: Jun 19, 2004

How do I make python print out where it's getting its lib path from? Somehow both 2.5.1 and 2.5.2 got installed on my Macbook Pro and 2.5.2 is pointing to a different lib path from 2.5.1 and I want to know where it's pointing at and how to change it. I tried googling but maybe I didn't look up the right thing? ("python change lib path")

edit: ahh, the PYTHONPATH environment variable

ashgromnies fucked around with this message at 21:24 on Apr 9, 2008

# ? Apr 9, 2008 21:19

No Safe Word: Feb 26, 2005

Anyone used any of the numerous python text parsing libraries out there? I'm playing around with pyparsing and having a bit of a time with it and was wondering: a) are there better options, or b) does anyone know pyparsing well enough that I should post questions here? I don't have anything specific yet, but it might be nice to know who has used what.

# ? Apr 9, 2008 22:12

Habnabit: Dec 30, 2007; lift your skinny fists like
antennas in germany.

No Safe Word posted:

Anyone used any of the numerous python text parsing libraries out there? I'm playing around with pyparsing and having a bit of a time with it and was wondering: a) are there better options, or b) does anyone know pyparsing well enough that I should post questions here? I don't have anything specific yet, but it might be nice to know who has used what.

I like pyparsing the best out of all of the python text parsers I've seen. I'm definitely not the best, but I can try to help you with problems. I've been working with for a little over a year. It's pretty slow, though, so you shouldn't use it if speed is a concern. I use it for lexing wiki pages, and it's fast enough to work with caching, but it definitely wouldn't work if the page was lexed every time it was loaded.

Habnabit fucked around with this message at 04:43 on Apr 10, 2008

# ? Apr 10, 2008 04:40

deimos: Nov 30, 2006; Forget it man this bat is whack, it's got poobrain!

Just found this article, well worth the stupid free registration, it's an awesome decorator explanation: http://www.linux-mag.com/id/5377

deimos fucked around with this message at 07:08 on Apr 10, 2008

# ? Apr 10, 2008 07:04

No Safe Word: Feb 26, 2005

Habnabit posted:

I like pyparsing the best out of all of the python text parsers I've seen. I'm definitely not the best, but I can try to help you with problems. I've been working with for a little over a year. It's pretty slow, though, so you shouldn't use it if speed is a concern. I use it for lexing wiki pages, and it's fast enough to work with caching, but it definitely wouldn't work if the page was lexed every time it was loaded.

Okay, well I guess this qualifies as a short question and the thread isn't exactly busting with other questions so here goes.

I'm trying to write a stat file parser for TF2 (I guess I'm a statwhore :byewhore:

), but it uses some funky JSON-like syntax that should be easy to write a parser for using pyparsing but I'm having a bitch of a time understanding why some of it doesn't work. Here's a cut-down sample file:

code:

<!-- dmx encoding keyvalues2 1 format dmx 1 -->
"PlayerStats"
{
	"id" "elementid" "076a075f-a605-42d9-a8b1-2478c0f008c5"
	"aClassStats" "element_array" 
	[
		"ClassStats_t"
		{
			"id" "elementid" "ab132a4c-0e10-49c1-8ee4-811b090568a4"
			"accumulated" "RoundStats_t"
			{
				"id" "elementid" "eb9b2473-2189-4dcd-b7b3-c15ff7500d39"
				"iBackstabs" "int" "0"
				"iBuildingsBuilt" "int" "0"
				<snip>
			}
			"comment: classname" "string" "Scout"
			"iNumberOfRounds" "int" "1609"
			"iPlayerClass" "int" "1"
			"max" "RoundStats_t"
			{
				"id" "elementid" "8de50328-cb14-4fc0-b458-f29c0329c8cf"
				"iBackstabs" "int" "0"
				"iBuildingsBuilt" "int" "0"
				"iSentryKills" "int" "0"
				<snip>
			}
		},
		"ClassStats_t"
		{
			"id" "elementid" "fa0703bc-08b8-4964-934b-18bfad54372c"
			"accumulated" "RoundStats_t"
			{
				"id" "elementid" "f3bf5f05-db8d-4542-8c8a-6f2ba43ce307"
				"iBackstabs" "int" "0"
				"iBuildingsBuilt" "int" "0"
				<snip>
			}
			"comment: classname" "string" "Sniper"
			"iNumberOfRounds" "int" "859"
			"iPlayerClass" "int" "2"
			"max" "RoundStats_t"
			{
				"id" "elementid" "178ae1d7-abd1-4e6d-98a3-616f2729c5b3"
				"iBackstabs" "int" "0"
				"iBuildingsBuilt" "int" "0"
				<snip>
			}
		}
	]
	"iTimestamp" "int" "236806956"
	"iVersion" "int" "0"
	"SteamID" "int" "30350757"
}

I <snip>'ed repetitive portions and cut some other stuff for brevity of course.

So, the pseudo-BNF I worked up looks like:

code:

item :=  <name>  <datatype>  <value>
list :=  <name>  [<datatype>]  "["  (<object>,)+  "]"
object := <name>  [<datatype>]  "{" (<item>|<list>)+ "}"

Where name, datatype, and value are really all just double-quoted strings, [] means optional, and + means one or more. So, here's the pyparsing code I came up with:

code:

statComment = htmlComment
statValue = dblQuotedString
statName = dblQuotedString
statDataType = dblQuotedString

statObject = Forward()
statItem = statName + statDataType + statValue
statList = statName + Optional(statDataType) + delimitedList(statObject)
statObject << statName + Optional(statDataType) + \
    Literal("{") + OneOrMore(statItem | statList) + Literal("}")
statFile = statComment + statObject

But when I try and do a statFile.parse on that data I always get:
pyparsing.ParseException: Expected "}" (at char 132), (line:5, col:5), which refers to the line that starts with "aClassStats". It's like the failure is in the OR'ing of the statItem and statList, though I'm going to try parsing each individual line with all the objects and see if it matches where I expect. But if anything is glaringly wrong let me know.

# ? Apr 10, 2008 17:44

mightygerm: Jun 29, 2002

does python not have a do ... while looping structure?
If not, is there a way I can emulate it without having to write my code blocks twice?

# ? Apr 10, 2008 19:49

Git: Aug 21, 2004

Mighty Germ posted:

does python not have a do ... while looping structure?
If not, is there a way I can emulate it without having to write my code blocks twice?

It doesn't have one as far as I'm aware, but PEP 315 proposes one.

I guess the equivalent would be:

code:

while 1:
    ...
    if not condition:
        break

Git fucked around with this message at 20:11 on Apr 10, 2008

# ? Apr 10, 2008 20:07

other people: Jun 27, 2004; Associate Christ

I have a list that I want to sort. The list would look something likee this:
[python]
[['/mnt/Local/laura', 'IMG_0001.JPG', 1207277478.0], ['/mnt/Local/laura', 'IMG_0002.JPG', 1207277490.0], ['/mnt/Local/laura', 'IMG_0006.JPG', 1207277830.0], ['/mnt/Local/laura', 'IMG_0005.JPG', 1207277795.0], ['/mnt/Local/laura', 'IMG_0004.JPG', 1207277782.0]]
[/python]

I want the list sorted by the third value in each item. I know I can do list.sort() with a flat list, but these are lists within lists, and I have no clue how to proceed.

Maybe this is just highlighting my lack of skill with python, but I find the documentation much harder to understand than, for example, php.

# ? Apr 10, 2008 20:27

No Safe Word: Feb 26, 2005

Kaluza-Klein posted:

I have a list that I want to sort. The list would look something likee this:
[python]
[['/mnt/Local/laura', 'IMG_0001.JPG', 1207277478.0], ['/mnt/Local/laura', 'IMG_0002.JPG', 1207277490.0], ['/mnt/Local/laura', 'IMG_0006.JPG', 1207277830.0], ['/mnt/Local/laura', 'IMG_0005.JPG', 1207277795.0], ['/mnt/Local/laura', 'IMG_0004.JPG', 1207277782.0]]
[/python]

I want the list sorted by the third value in each item. I know I can do list.sort() with a flat list, but these are lists within lists, and I have no clue how to proceed.

Maybe this is just highlighting my lack of skill with python, but I find the documentation much harder to understand than, for example, php.

code:

In [7]: random.shuffle(L)

In [8]: L
Out[8]:
[['/mnt/Local/laura', 'IMG_0006.JPG', 1207277830.0],
 ['/mnt/Local/laura', 'IMG_0001.JPG', 1207277478.0],
 ['/mnt/Local/laura', 'IMG_0005.JPG', 1207277795.0],
 ['/mnt/Local/laura', 'IMG_0002.JPG', 1207277490.0],
 ['/mnt/Local/laura', 'IMG_0004.JPG', 1207277782.0]]

In [9]: L.sort(lambda x,y: cmp(x[2], y[2]))

In [10]: L
Out[10]:
[['/mnt/Local/laura', 'IMG_0001.JPG', 1207277478.0],
 ['/mnt/Local/laura', 'IMG_0002.JPG', 1207277490.0],
 ['/mnt/Local/laura', 'IMG_0004.JPG', 1207277782.0],
 ['/mnt/Local/laura', 'IMG_0005.JPG', 1207277795.0],
 ['/mnt/Local/laura', 'IMG_0006.JPG', 1207277830.0]]

You can specify a sorting function that takes two arguments and returns -1, 0, 1 for the proper comparison.

Another better example (since sorting these normally produces the same results):

code:

In [11]: L = [(0, 5), (1, 4), (2, 3), (3, 2), (4, 1), (5, 0)]

In [12]: L.sort(lambda x,y: cmp(x[1], y[1]))

In [13]: L
Out[13]: [(5, 0), (4, 1), (3, 2), (2, 3), (1, 4), (0, 5)]

# ? Apr 10, 2008 20:43

Git: Aug 21, 2004

Kaluza-Klein posted:

I want the list sorted by the third value in each item.

There may be a better way to do this, but you can do it using your own sort function.

code:

>>> lst1 = ['lol', '1', '3']
>>> lst2 = ['lol', '2', '2']
>>> lst3 = ['lol', '3', '1']
>>> biglist = [lst2,lst1,lst3]
>>> biglist.sort()
>>> biglist
[['lol', '1', '3'], ['lol', '2', '2'], ['lol', '3', '1']]
>>> def asort(x, y):
...     if x[2] > y[2]:
...             return 1
...     elif x[2]==y[2]:
...             return 0
...     else:
...             return -1
...
>>> biglist.sort(asort)
>>> biglist
[['lol', '3', '1'], ['lol', '2', '2'], ['lol', '1', '3']]

This page seems pretty informative on sorting. But yeah, there's probably a better way to do this.

e: damnit.

# ? Apr 10, 2008 20:53

other people: Jun 27, 2004; Associate Christ

No Safe Word posted:

code:

In [7]: random.shuffle(L)

In [8]: L
Out[8]:
[['/mnt/Local/laura', 'IMG_0006.JPG', 1207277830.0],
 ['/mnt/Local/laura', 'IMG_0001.JPG', 1207277478.0],
 ['/mnt/Local/laura', 'IMG_0005.JPG', 1207277795.0],
 ['/mnt/Local/laura', 'IMG_0002.JPG', 1207277490.0],
 ['/mnt/Local/laura', 'IMG_0004.JPG', 1207277782.0]]

In [9]: L.sort(lambda x,y: cmp(x[2], y[2]))

In [10]: L
Out[10]:
[['/mnt/Local/laura', 'IMG_0001.JPG', 1207277478.0],
 ['/mnt/Local/laura', 'IMG_0002.JPG', 1207277490.0],
 ['/mnt/Local/laura', 'IMG_0004.JPG', 1207277782.0],
 ['/mnt/Local/laura', 'IMG_0005.JPG', 1207277795.0],
 ['/mnt/Local/laura', 'IMG_0006.JPG', 1207277830.0]]

You can specify a sorting function that takes two arguments and returns -1, 0, 1 for the proper comparison.

Another better example (since sorting these normally produces the same results):

code:

In [11]: L = [(0, 5), (1, 4), (2, 3), (3, 2), (4, 1), (5, 0)]

In [12]: L.sort(lambda x,y: cmp(x[1], y[1]))

In [13]: L
Out[13]: [(5, 0), (4, 1), (3, 2), (2, 3), (1, 4), (0, 5)]

Woah, thank you! I never would have figured that out myself.

# ? Apr 10, 2008 21:06

Habnabit: Dec 30, 2007; lift your skinny fists like
antennas in germany.

Writing your own cmp function is depreciated and just plain icky, really. Use a key function, which is much, much cleaner. A key function is passed one parameter multiple times: once for each item in the list to be sorted. The list is then sorted by the returned values.

code:

>>> pprint.pprint(l)
[['/mnt/Local/laura', 'IMG_0001.JPG', 1207277478.0],
 ['/mnt/Local/laura', 'IMG_0002.JPG', 1207277490.0],
 ['/mnt/Local/laura', 'IMG_0006.JPG', 1207277830.0],
 ['/mnt/Local/laura', 'IMG_0005.JPG', 1207277795.0],
 ['/mnt/Local/laura', 'IMG_0004.JPG', 1207277782.0]]

>>> import operator
>>> l.sort(key=operator.itemgetter(2))
>>> pprint.pprint(l)
[['/mnt/Local/laura', 'IMG_0001.JPG', 1207277478.0],
 ['/mnt/Local/laura', 'IMG_0002.JPG', 1207277490.0],
 ['/mnt/Local/laura', 'IMG_0004.JPG', 1207277782.0],
 ['/mnt/Local/laura', 'IMG_0005.JPG', 1207277795.0],
 ['/mnt/Local/laura', 'IMG_0006.JPG', 1207277830.0]]

itemgetter returns an object that works like this:
operator.itemgetter(2)(list) -> list[2]

(Working on the pyparsing code, will be up in a minute.)

Habnabit fucked around with this message at 09:03 on Apr 11, 2008

# ? Apr 11, 2008 08:59

duck monster: Dec 15, 2004

Mighty Germ posted:

does python not have a do ... while looping structure?
If not, is there a way I can emulate it without having to write my code blocks twice?

code:


keep_looping_bitch = true

while keep_looping_bitch:
     #
     # code
     #
     keep_looping_bitch = not (condition)

should emulate

code:

repeat:
     #
     #
     #
until (condition)

# ? Apr 11, 2008 09:58

Strong Sauce: Jul 2, 2003; You know I am not really your father.

Can anyone who has worked with stackless / threads in general for Python give an evaluation of it? From reading its documentation it seems that they are very small in size and fast yet I rarely hear about anyone using them for projects (sans EVE online).

# ? Apr 11, 2008 14:18

deimos: Nov 30, 2006; Forget it man this bat is whack, it's got poobrain!

I just found out about dabo it's like django for client applications. It wraps wxPython, making it a bit more pythonic and overall nicer to work with. I haven't done an application in it but I think I have something I want to throw at it.

# ? Apr 11, 2008 14:45

Juomes: Apr 8, 2008

I remember coming across a 'website game' (where each page is a riddle leading you to the next page) but all the problems were problems to solve in Python.
Anyone know the link?

# ? Apr 11, 2008 16:13

deimos: Nov 30, 2006; Forget it man this bat is whack, it's got poobrain!

Juomes posted:

I remember coming across a 'website game' (where each page is a riddle leading you to the next page) but all the problems were problems to solve in Python.
Anyone know the link?

http://www.pythonchallenge.com/

# ? Apr 11, 2008 16:48

Juomes: Apr 8, 2008

deimos posted:

http://www.pythonchallenge.com/

Thanks. I knew it was going to be something obvious.

Also I'm thankful I remembered about the site because I was out of ideas to practice my newly learned Python knowledge.

# ? Apr 12, 2008 14:30

the talent deficit: Dec 20, 2003; self-deprecation is a very british trait, and problems can arise when the british attempt to do so with a foreign culture

I'm newish to python, and I've been using TextMate (on OSX) to do most of my editing. However, I'm getting frequent indent errors from code that looks, to my eye, fine. Mostly from code copy/pasted from somewhere. Often I have to delete and whitespace and reinsert the indentation to fix it. Any idea what I'm doing wrong?

# ? Apr 13, 2008 21:20

Git: Aug 21, 2004

the talent deficit posted:

Any idea what I'm doing wrong?

Tell TextMate to use soft tabs, and set the option to re-indent pasted text in its preferences.

e: Actually, you probably don't need to use soft tabs, if hard tabs are your thing.

Git fucked around with this message at 21:28 on Apr 13, 2008

# ? Apr 13, 2008 21:26

tehk: Mar 10, 2006; [-4] Flaw: Heart Broken - Tehk is extremely lonely. The Gay Empire's ultimate weapon finds it hard to have time for love.

Like Git said its probably a bad mix of spaces*4 and tabs. I know many editors support an optional convert tabs to spaces function(either realtime or upon save) so you might want to check that out in textmate.

# ? Apr 13, 2008 21:47

No Safe Word: Feb 26, 2005

Looks like Sun's App Engine/AWS-alike will handle python as well: http://research.sun.com/spotlight/2008/2008-04-09_caroline.html (see the graphic)

:woop:

# ? Apr 14, 2008 21:36

m0nk3yz: Mar 13, 2002; Behold the power of cheese!

Figured I'd ask - any Boston/Boston Metro area Python people (or people getting into Python) looking around for a Job()?

# ? Apr 16, 2008 02:29

such a nice boy: Mar 22, 2002

m0nk3yz posted:

Figured I'd ask - any Boston/Boston Metro area Python people (or people getting into Python) looking around for a Job()?

I will move to Boston for a good python job.

# ? Apr 16, 2008 02:47

Bozart: Oct 28, 2006; Give me the finger.

Hey, I'm a programmer who's looking to pick up Python. I'm an expert at matlab, and proficient in C, C++, and VB. I'm mainly intersted in Python because I'm tired of how crappy Matlab's oo stuff is.

I was thinking of learning python by playing around with Orange and NumPy. Are these good starting points for me (given that I don't care about the web stuff) or should I go for something else like PyGame?

# ? Apr 16, 2008 03:07

hairacles: Mar 1, 2006; Ba-dunk-a-dunk

I'm making a program for a class where I was told to use the built-in priority queue. However, I was supposed to override the built-in __cmp__ method because because what we are passing into the queue is an array, which python can't compare. The example I was given was:

code:

class HeapItems:
    def __init__(self,name,rank):
        self.name=name
        self.rank=rank
    
    def __cmp__(self,other):
        '''__cmp__ is supposed to return a negative number if self is
        "smaller" than other, 0 if equal, and a positive number if
        "greater."'''
        return  self.rank-other.rank

How could I get it to just compare the [1] item in the array, which would be rank?

# ? Apr 16, 2008 07:11

mightygerm: Jun 29, 2002

Bozart posted:

Hey, I'm a programmer who's looking to pick up Python. I'm an expert at matlab, and proficient in C, C++, and VB. I'm mainly intersted in Python because I'm tired of how crappy Matlab's oo stuff is.

I was thinking of learning python by playing around with Orange and NumPy. Are these good starting points for me (given that I don't care about the web stuff) or should I go for something else like PyGame?

I was in a similar situation as you (used matlab/shell scripting at work), and just started recently learning Python. I picked up the Programming Python book, along with using the online official Python tutorial and the api for the packages I intended to use. I started converting my old scripts and programs over to Python and got a good grasp of the language.

# ? Apr 16, 2008 11:15

mightygerm: Jun 29, 2002

hairacles posted:

I'm making a program for a class where I was told to use the built-in priority queue. However, I was supposed to override the built-in __cmp__ method because because what we are passing into the queue is an array, which python can't compare. The example I was given was:
code:
class HeapItems:
    def __init__(self,name,rank):
        self.name=name
        self.rank=rank
    
    def __cmp__(self,other):
        '''__cmp__ is supposed to return a negative number if self is
        "smaller" than other, 0 if equal, and a positive number if
        "greater."'''
        return  self.rank-other.rank
How could I get it to just compare the [1] item in the array, which would be rank?

I don't think I understand your question, can you provide an example input/output of the data you intend you use?

# ? Apr 16, 2008 11:18

hairacles: Mar 1, 2006; Ba-dunk-a-dunk

Yeah, no problem. The program is for an AI class, and we're doing an intelligent search to quickly find a solution to an 8-puzzle. http://en.wikipedia.org/wiki/8-puzzleSpecifically, A* search. An example of whats being passed in is [2876549, 8], where the first number represents the puzzle being looked at, and the second number is how close the current state is to the solution. So I would be doing heappush(queue, array). So we are supposed to override the __cmp__ so it examines the second item in the array, since the built in heap functions aren't able to recognize what to do when given an array and not a number. The professor never really explained much about how we were supposed to do this, so I might be missing something obvious. What I have so far-

code:

def astar(self, state, heuristic):
    pqueue = []
    heappush(pq, [state, distance to goal])
    while len(pqueue) != 0:
        heappop(pqueue)
        ...stuff...
        for i in children of current satte
        heappush(pqueue, [i, distance of that child to goal]

plus the code I have listed above, which I am a bit confused about.

# ? Apr 16, 2008 16:48

JoeNotCharles: Mar 3, 2005; Yet beyond each tree there are only more trees.

Well, you've got two problems here. The first is how to override __cmp__ for an array, and the other is what goes in the __cmp__ routine.

The problem is, you can't really override __cmp__ on the "list" class (Python has no separate arrays, you're really using lists) because it's a builtin class and you can't change it. You'll have to make your own class and convert to and from it before you put it on the heap.

code:

class StateArray(list):
  def __cmp__(self, other):
    # cmp code goes here

...

def astar(self, state, heuristic):
  pqueue = []
  heappush(pq, [b]StateArray([/b][state, distance to goal][b])[/b])
  ...

Because StateArray descends from list, it acts just like a regular list except for the __cmp__ method.

Most functions that use compare objects using __cmp__ will take an optional parameter so you can pass a standalone function instead (so you could say def compareStates(a, b): ... heappush(pq, [state, distance to coal], comparseStates)), but heappush doesn't seem to have that, which is an annoying oversight.

Now that you know where to put the __cmp__ function, it should be easy to change the one you were given for HeapItems to use [1] instead of .rank.

...however, this seems pretty roundabout. Are you sure you weren't supposed to just change astar() to use HeapItems instead of an array?

# ? Apr 16, 2008 17:03

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# ? Apr 28, 2024 05:20

Bozart: Oct 28, 2006; Give me the finger.

Mighty Germ posted:

I was in a similar situation as you (used matlab/shell scripting at work), and just started recently learning Python. I picked up the Programming Python book, along with using the online official Python tutorial and the api for the packages I intended to use. I started converting my old scripts and programs over to Python and got a good grasp of the language.

Alright then, cool. I got Learning Python and read the Tutorial, so I think I am good to go.

The only annoying thing is that the help for built in classes and methods sucks hard after Matlab's great help system. I'll have to spend time bumming around on the python wiki to see if they have better documentation there. Is the Programming Python book significantly better or more in depth than Learning Python? I figure it has a different focus because it has a different animal on the cover!

# ? Apr 16, 2008 18:14

The Something Awful Forums > Discussion > Serious Hardware/Software Crap > The Cavern of COBOL > Python information and short questions megathread.

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