Too Many if Statements?

**bruno at modulix** · Feb 7 '06, 05:15 PM

Re: Too Many if Statements?

slogging_away wrote:[color=blue]
> Hi - I'm running Python 2.4.2 (#67, Sep 28 2005, 12:41:11) [MSC v.1310
> 32 bit (Intel)] on win32, and have a script that makes numerous checks
> on text files, (configuration files), so discrepancies can be reported.
> The script works fine but it appears that I may have hit a wall with
> 'if' statements.
>
> Due to the number of checks perfromed by the script on the text files,
> (over 500), there are quite a few 'if' statements in the script, (over
> 1150). It seems that it is at the point that when I add any additional
> 'if' statements the script will not run. No error is produced - it
> just returns to the python prompt much the same as when a successful
> 'Check Module' command is selected. If I delete some other 'if'
> statements the new ones work so it appears that it has hit a limit on
> the number of 'if' statements. This has stunted any further checks for
> the script to make on the text files.
>
> Hs anyone ever run into this sort of thing?
>[/color]

Nope - but I never saw any code block with 1150+ tests in it neither :-/

Smells like a design problem anyway. Have you considered refactoring
your code ?

--
bruno desthuilliers
python -c "print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
p in 'onurb@xiludom. gro'.split('@')])"

**snoe** · Feb 7 '06, 05:15 PM

Re: Too Many if Statements?

slogging_away wrote:[color=blue]
> Hi - I'm running Python 2.4.2 (#67, Sep 28 2005, 12:41:11) [MSC v.1310
> 32 bit (Intel)] on win32, and have a script that makes numerous checks
> on text files, (configuration files), so discrepancies can be reported.
> The script works fine but it appears that I may have hit a wall with
> 'if' statements.
>
> Due to the number of checks perfromed by the script on the text files,
> (over 500), there are quite a few 'if' statements in the script, (over
> 1150). It seems that it is at the point that when I add any additional
> 'if' statements the script will not run. No error is produced - it
> just returns to the python prompt much the same as when a successful
> 'Check Module' command is selected. If I delete some other 'if'
> statements the new ones work so it appears that it has hit a limit on
> the number of 'if' statements. This has stunted any further checks for
> the script to make on the text files.
>
> Hs anyone ever run into this sort of thing?[/color]

I can't say I've run into it before but your description makes me think
there are other approaches you could take. Does splitting the large
number of if statements into separate functions help at all?
If you're checking some text to see if a number of static strings are
contained therein, you could put the test strings into a list and loop
through...somet hing like this (untested):

tests = [
'looking for this string',
'and this one',
'am i in the text'
] # etc...

for test in tests:
if test not in text:
raise LookupError

**slogging_away** · Feb 7 '06, 05:25 PM

Re: Too Many if Statements?

I don't consider myself to be a seasoned programmer so if you mean
redesigning the script to make the checks and therefore reduce the
number of 'if' statements, I'm not sure if that can be done. The
script needs to make numerous checks for the existence of particular
strings within the configuration file. It also uses 'if' statements to
determine what type of file is being examined, etc.. If an error is
encounterd it writes warning messages to a master file. I guess what I
am trying to say is that in order to make the many checks on the
configuration files I do not know of any other way than to check for
the existance of particular statements, (strings), and then report on
those if they are incorrect or missing - hence at least one 'if'
statement for every check.

I appreciate the feedback though!

**slogging_away** · Feb 7 '06, 05:25 PM

Re: Too Many if Statements?

Ah! I see what you are saying snoe, (and most likely what bruno at
modulix was recommending). That technique should provide a workaround
to the direct 'if' approach currently used and also offer some
modularity to the logic as well.

Thank you for pointing me in the right direction - I'll give it a go.

**bruno at modulix** · Feb 7 '06, 06:15 PM

Re: Too Many if Statements?

slogging_away wrote:[color=blue]
> I don't consider myself to be a seasoned programmer[/color]

nor do I.
[color=blue]
> so if you mean
> redesigning the script to make the checks and therefore reduce the
> number of 'if' statements, I'm not sure if that can be done.[/color]

I strongly doubt it could *not* be done !-)
[color=blue]
> The
> script needs to make numerous checks for the existence of particular
> strings within the configuration file. It also uses 'if' statements to
> determine what type of file is being examined, etc.. If an error is
> encounterd it writes warning messages to a master file.[/color]

Yeps, that's pretty common with this kind of scripts. I recently had a
script doing thousands of regexp substitutions, image resizing, file
moves, database inserts etc, and of course a fair amount of logging. And
I can tell you that there many few "if" in this code.
[color=blue]
> I guess what I
> am trying to say is that in order to make the many checks on the
> configuration files I do not know of any other way than to check for
> the existance of particular statements, (strings), and then report on
> those if they are incorrect or missing - hence at least one 'if'
> statement for every check.[/color]

Suppose you have to match a line against a list of regexp and log if it
doesn't match. You could of course repeat the whole code for each
regexp, ie:

if not re.match(r'a/regexp/here', line):
log('a first message')

if not re.match(r'anot her/regexp/here', line):
log('another message')

(... 150 regexps later ...)

if not re.match(r'150/regexps/later', line):
log('pfww, getting tired of copy/pasting')

etc...

But you could also factor much of it:

def checkMatch(line , regexp, msg):
if not re.match(regexp , line):
log(msg)

then have a list of regexps/messages pairs and:
for exp, msg in regexps:
checkMatch(line , exp, msg)

And now, you can add as many thousands regexps you want, you still have
one (and only one) if in the code (well, in this snippet at least...).
[color=blue]
> I appreciate the feedback though![/color]

You're welcome !-)

--
bruno desthuilliers
python -c "print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
p in 'onurb@xiludom. gro'.split('@')])"

**Alan Morgan** · Feb 7 '06, 07:15 PM

Re: Too Many if Statements?

In article <1139330447.716 190.247940@z14g 2000cwz.googleg roups.com>,
slogging_away <hinnc@yahoo.co m> wrote:[color=blue]
>Hi - I'm running Python 2.4.2 (#67, Sep 28 2005, 12:41:11) [MSC v.1310
>32 bit (Intel)] on win32, and have a script that makes numerous checks
>on text files, (configuration files), so discrepancies can be reported.
> The script works fine but it appears that I may have hit a wall with
>'if' statements.
>
>Due to the number of checks perfromed by the script on the text files,
>(over 500), there are quite a few 'if' statements in the script, (over
>1150). It seems that it is at the point that when I add any additional
>'if' statements the script will not run. No error is produced - it
>just returns to the python prompt much the same as when a successful
>'Check Module' command is selected. If I delete some other 'if'
>statements the new ones work so it appears that it has hit a limit on
>the number of 'if' statements. This has stunted any further checks for
>the script to make on the text files.
>
>Hs anyone ever run into this sort of thing?[/color]

I generated files with 10000, 25000, and 50000 simple if statements and ran
them. 10000 was okay, 25000 gave a bizarre internal error, and 50000 segfaulted
and died. My system has plenty of memory and it isn't obvious to me why python
should be so bothered about this. I'm not sure why I can have 10x the number of
if statements that cause you trouble. There might be some overall limitation
on the number of statements in a file.

Alan
--
Defendit numerus

**Casey Hawthorne** · Feb 7 '06, 09:15 PM

Re: Too Many if Statements?

Try the state(s) pattern!

"slogging_a way" <hinnc@yahoo.co m> wrote:
[color=blue]
>Hi - I'm running Python 2.4.2 (#67, Sep 28 2005, 12:41:11) [MSC v.1310
>32 bit (Intel)] on win32, and have a script that makes numerous checks
>on text files, (configuration files), so discrepancies can be reported.
> The script works fine but it appears that I may have hit a wall with
>'if' statements.
>
>Due to the number of checks perfromed by the script on the text files,
>(over 500), there are quite a few 'if' statements in the script, (over
>1150). It seems that it is at the point that when I add any additional
>'if' statements the script will not run. No error is produced - it
>just returns to the python prompt much the same as when a successful
>'Check Module' command is selected. If I delete some other 'if'
>statements the new ones work so it appears that it has hit a limit on
>the number of 'if' statements. This has stunted any further checks for
>the script to make on the text files.
>
>Hs anyone ever run into this sort of thing?[/color]
--
Regards,
Casey

**Bryan Olson** · Feb 7 '06, 10:25 PM

Re: Too Many if Statements?

Alan Morgan wrote:[color=blue]
> slogging_away wrote:
>[color=green]
>>Hi - I'm running Python 2.4.2 (#67, Sep 28 2005, 12:41:11) [MSC v.1310
>>32 bit (Intel)] on win32, and have a script that makes numerous checks
>>on text files, (configuration files), so discrepancies can be reported.
>>The script works fine but it appears that I may have hit a wall with
>>'if' statements.
>>
>>Due to the number of checks perfromed by the script on the text files,
>>(over 500), there are quite a few 'if' statements in the script, (over
>>1150). It seems that it is at the point that when I add any additional
>>'if' statements the script will not run. No error is produced - it
>>just returns to the python prompt much the same as when a successful
>>'Check Module' command is selected. If I delete some other 'if'
>>statements the new ones work so it appears that it has hit a limit on
>>the number of 'if' statements. This has stunted any further checks for
>>the script to make on the text files.
>>
>>Hs anyone ever run into this sort of thing?[/color]
>
>
> I generated files with 10000, 25000, and 50000 simple if statements and ran
> them. 10000 was okay, 25000 gave a bizarre internal error, and 50000 segfaulted
> and died. My system has plenty of memory and it isn't obvious to me why python
> should be so bothered about this. I'm not sure why I can have 10x the number of
> if statements that cause you trouble. There might be some overall limitation
> on the number of statements in a file.[/color]

I made a script with 100,000 if's, (code below) and it appears
to work on a couple systems, including Python 2.4.2 on Win32-XP.
So at first cut, it doesn't seem to be just the if-count that
triggers the bug.

Code that does *not* demo the error on my systems:

#! /usr/bin/env python

lines = ["""#! /usr/bin/env python

import random
c = 0
n = random.randrang e(10L**10)
"""]

for i in range(100000):
lines.append('i f n % random.randrang e(2, 1000) == 0: c += 1')
lines.append('p rint c')
lines.append('# #############')
progtext = '\n'.join(lines )

f = file('manyifs.p y', 'w')
f.write(progtex t)
f.close()

exec progtext

--
--Bryan

**slogging_away** · Feb 7 '06, 10:55 PM

Re: Too Many if Statements?

Hmmm - good responses all around. Thank you all for your valued
feedback.

Perhaps it's too may 'if' statements under the for XXX in range(x,x,x)
statement as most of the 'if' statements appear there. It could be
something entirely else. I'm afraid its a bug with Python, (if I try
and run it several times it keeps going to the IDLE console prompt and
it eventually crashes out of Python entirely).

Some useful suggestions were provided in terms of better design so that
may be my route at this point. Thanks again for all of your help!

**Terry Reedy** · Feb 7 '06, 11:05 PM

Re: Too Many if Statements?

"Bryan Olson" <fakeaddress@no where.org> wrote in message
news:GU8Gf.2289 9$Jd.6095@newss vr25.news.prodi gy.net...[color=blue]
> I made a script with 100,000 if's, (code below) and it appears
> to work on a couple systems, including Python 2.4.2 on Win32-XP.
> So at first cut, it doesn't seem to be just the if-count that
> triggers the bug.[/color]

The OP did not specify whether all of his if-tests were sequential as in
your test or if some were nested. I vaguely remember there being an indent
limit (40??).

tjr

**Alan Morgan** · Feb 7 '06, 11:25 PM

Re: Too Many if Statements?

In article <GU8Gf.22899$Jd .6095@newssvr25 .news.prodigy.n et>,
Bryan Olson <fakeaddress@no where.org> wrote:[color=blue]
>Alan Morgan wrote:[color=green]
>> slogging_away wrote:
>>[color=darkred]
>>>Hi - I'm running Python 2.4.2 (#67, Sep 28 2005, 12:41:11) [MSC v.1310
>>>32 bit (Intel)] on win32, and have a script that makes numerous checks
>>>on text files, (configuration files), so discrepancies can be reported.
>>>The script works fine but it appears that I may have hit a wall with
>>>'if' statements.
>>>[/color]
>> I generated files with 10000, 25000, and 50000 simple if statements and ran
>> them. 10000 was okay, 25000 gave a bizarre internal error, and 50000 segfaulted
>> and died. My system has plenty of memory and it isn't obvious to me why python
>> should be so bothered about this. I'm not sure why I can have 10x the number of
>> if statements that cause you trouble. There might be some overall limitation
>> on the number of statements in a file.[/color]
>
>I made a script with 100,000 if's, (code below) and it appears
>to work on a couple systems, including Python 2.4.2 on Win32-XP.
>So at first cut, it doesn't seem to be just the if-count that
>triggers the bug.[/color]

Mine was a simple

#!/usr/local/bin/python

zot=24999
if zot == 0:
print "It's 0"

if zot == 1:
print "It's 1"

.....

if zot == 24999:
print "It's 24999"

generated (I'm ashamed to admit) by a perl script. Is there any good reason why
it is failing? I'd prefer a "Too many silly walks in your program. Reduce!" to
a crash. I could experiment with putting the matching 'if' at the beginning
rather than at the end, but I'm not sure what that would tell me.

Alan
--
Defendit numerus

**Bryan Olson** · Feb 7 '06, 11:45 PM

Re: Too Many if Statements?

Terry Reedy wrote:[color=blue]
> "Bryan Olson" wrote:
>[color=green]
>>I made a script with 100,000 if's, (code below) and it appears
>>to work on a couple systems, including Python 2.4.2 on Win32-XP.
>>So at first cut, it doesn't seem to be just the if-count that
>>triggers the bug.[/color]
>
> The OP did not specify whether all of his if-tests were sequential as in
> your test or if some were nested. I vaguely remember there being an indent
> limit (40??).[/color]

A 40-level indent limit is reasonable (I may get around to looking
it up and/or testing it), but if we believe 'slogging' and Alan, what
we have here is an outright Python bug. They did not report a message
about static code being too deeply nested, nor about dynamic calls
exceeding a recursion limit. They reported incorrect behavior.

My favorite joke goes:

Patient: Doctor...doctor -- it hurts when I do that! (With 'that'
being some movement that is unusual but normally innocuous.)

Doctor: Don't do that.

Ah...cracks me up. Funny on so many levels.

--
--Bryan

**mensanator@aol.com** · Feb 7 '06, 11:45 PM

Re: Too Many if Statements?

slogging_away wrote:[color=blue]
> Hmmm - good responses all around. Thank you all for your valued
> feedback.
>
> Perhaps it's too may 'if' statements under the for XXX in range(x,x,x)[/color]

Have you tried xrange() instead of range()?
[color=blue]
> statement as most of the 'if' statements appear there. It could be
> something entirely else. I'm afraid its a bug with Python, (if I try
> and run it several times it keeps going to the IDLE console prompt and
> it eventually crashes out of Python entirely).
>
> Some useful suggestions were provided in terms of better design so that
> may be my route at this point. Thanks again for all of your help![/color]

**nnorwitz@gmail.com** · Feb 8 '06, 07:25 AM

Re: Too Many if Statements?

Alan Morgan wrote:[color=blue]
>
> generated (I'm ashamed to admit) by a perl script. Is there any good reason why
> it is failing? I'd prefer a "Too many silly walks in your program. Reduce!" to
> a crash.[/color]

Everyone,

Please file a bug report anytime you make Python crash!

http://sourceforge.net/tracker/?grou...70&atid=105470

If you aren't willing to deal with SF, at least send me source code
(not a description) that makes python crash.

n

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