Re: Too Many if Statements?
slogging_away wrote:
bruno at modulix wrote:
Looks like a memory problem then...
The system I am using has 2GB of memory, (unless you are syaing the
memory is faulty).
Nope, just that I don't know of any system with unlimited memory. BTW,
having 2GB of ram does not mean there are 2GB available for your program.
(And BTW, this is just one of the *possible* reasons of the problem
you've discovered. May be quite unrelated as well...)
Why storing error messages ? Why don't you just write'em out (be it to
stdout or to a file) ?
I guess I could do that, (write them to a file as they are discovered).
Well, this is how most programs do.
Right now the error messages are stored in the array and then the the
array is scanned via, a for loop and the error messages are written to
several files in different formats based on the severity of the errors,
(on a per device basis, a per severity basis, etc.). This keeps the
write statements to a minimum and in a central location of the script
instead of having several statements for each individual error message
spread throughout the script, (three write statements per error message
at over 500 error messages would be a significant change).
This is a design problem, not an implementation problem. Just factor out
the part that do the error message dispatch into a function, then call
this function instead of storing the message. Or even better, use an
existing logging library...
Not to complain but if I can't use arrays then thats a pretty
significant limitation.
Please understand that available memory is a limitation of the *system*
- you'd get the same limitation with *every* language ever (well, if you
know of a language that expand free ram ad infinitum, please let us know !-)
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Re: Too Many if Statements?
Now that I know the root cause of the problem, I can write around it as suggested by Steve Holden and Terry Reedy, (and others). In fact, it has helped me in a way as I am thinking not in terms of the easiest solution, (read; the first one that comes to mind), but more effcient and cleaner ways to write a section of code to accomplish the same objective. The key was identifying the root cause which was provided by the error message seen only at the command line level and by contibutors to this post. Thanks again for everyone's suggestions and expertise. -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
On Sat, 11 Feb 2006 15:40:49 -0500, Terry Reedy [EMAIL PROTECTED] wrote:
Steve Holden [EMAIL PROTECTED] wrote in message
news:[EMAIL PROTECTED]
Clearly it would be a good idea to remove whatever problem is causing
the error,
The problem (see my post of the com_backpatch code) is writing a compound
statement (here a for loop) with a body so large as to require a jump of
more than 64K bytes in the compiled bytecode (ie, from the test at the top
of the loop to the code that follows after the loop). Until the jump limit
is raised (likely a long wait ;-), the OP must factor some of the code out
of the loop.
Easy example:
def test(n):
... while True:
... try: co = compile('if x:\n'+ n*' a=1\n','','exec')
... except Exception,e: break
... n += 1
... print 'Stopped at n=%s due to %s: %s'%(n, e.__class__.__name__,e)
...
get an idea of where to start that:
import dis
n=3
dis.dis( compile('if x:\n'+ n*' a=1\n','','exec'))
1 0 LOAD_NAME0 (x)
3 JUMP_IF_FALSE 22 (to 28)
6 POP_TOP
2 7 LOAD_CONST 0 (1)
10 STORE_NAME 1 (a)
3 13 LOAD_CONST 0 (1)
16 STORE_NAME 1 (a)
4 19 LOAD_CONST 0 (1)
22 STORE_NAME 1 (a)
25 JUMP_FORWARD 1 (to 29)
28 POP_TOP
29 LOAD_CONST 1 (None)
32 RETURN_VALUE
(2**16-7)/(13-7)
10921
back off 1
test(10920)
Stopped at n=10922 due to SystemError: com_backpatch: offset too large
Decided to test the exact 65536 jump with code chunks of 16 byte-codes and one
chunk at the end to make 16 with the last JUMP_FORWARD.
n=4095
dis.dis( compile('if x:\n'+ n*' a=1+2,4 \n'+' x=0,x','','exec'))
Traceback (most recent call last):
File stdin, line 1, in ?
SystemError: com_backpatch: offset too large
n=4094
dis.dis( compile('if x:\n'+ n*' a=1+2,4 \n'+' x=0,x','','exec'))
1 0 LOAD_NAME0 (x)
3 JUMP_IF_FALSE65520 (to 65526)
6 POP_TOP
2 7 LOAD_CONST 0 (1)
10 LOAD_CONST 1 (2)
13 BINARY_ADD
14 LOAD_CONST 2 (4)
17 BUILD_TUPLE 2
20 STORE_NAME 1 (a)
3 23 LOAD_CONST 0 (1)
So the corner case of 2**16 is ok. Believe it or not, I once discovered a
compiler
error based on optimizing a 2**16-involving loop condition as if it were 0 and
the
loop didn't execute! IIRC, I bumped into it processing an array of records with
a stride of
exactly 2**n and it thought it could calculate a 16-bit number of strides for
end of loop.
No good for arraysize/stridesize==2**16 ;-)
If the OP really HAD to, he could always (untested) break
if cond:
too
large
else:
two
large,also
into
if cond:
too
else:
two
if cond:
large
else:
large,also
but that reads gawdawfully. (So, I imagine, does about any code hitting the
offset limit ;-)
If it's a matter of too many elifs, the OP could break that more readably, e.g.
(untested)
done=True
if cond:
bla
elif c2:
bla 2
...
elif c456:
bla456
else:
done=False
more, done = not done,True
if more and c457:
bla c457
elif c458:
bla458
...
elif c1012:
bla1012
else:
done = False
more, done = not done,True
... etc
But the OP should find another approach I think,
because this is still disgusting code ;-)
Regards,
Bengt Richter
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Re: Too Many if Statements?
slogging_away [EMAIL PROTECTED] wrote in message
news:[EMAIL PROTECTED]
SystemError: com_backpatch: offset too large
This message is generated in the backpatch function in Python/compile.c in
the source tree. (See below: sorry, tab indents did not survive cut and
paste operation.) As the comment says, and the code shows, it patches in a
2-byte jump offset. The error is raised if the offset is not 0 after
beinging divided by 256 twice (ie, by 65536). This code is called from any
function that compiles a construct that potentially jumps: for, while,
if/elif, and short-circuiting logic expressions.
To me, this message indicates not a bug but a mismatch between code demand
and interpreter capability. The solution is to reduce the demand. In the
present case, changing
for line in file:
extra-long body
to
def checkline(line):
extra-long body
for line in file:
checkline(line)
might be sufficient. If not, break up the extra-lone body into multiple
pieces.
Terry Jan Reedy
static void
com_backpatch(struct compiling *c, int anchor)
{
unsigned char *code = (unsigned char *) PyString_AS_STRING(c-c_code);
int target = c-c_nexti;
int dist;
int prev;
for (;;) {
/* Make the JUMP instruction at anchor point to target */
prev = code[anchor] + (code[anchor+1] 8);
dist = target - (anchor+2);
code[anchor] = dist 0xff;
dist = 8;
code[anchor+1] = dist;
dist = 8;
if (dist) {
com_error(c, PyExc_SystemError,
com_backpatch: offset too large);
break;
}
if (!prev)
break;
anchor -= prev;
}
}
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Re: Too Many if Statements?
slogging_away wrote: Magnus Lycka wrote: What happens if you run it from the command line instead of IDLE? After all, it might be some problem in IDLE involved here. Even if it doesn't work correctly outside IDLE, I was thinking that IDLE might swallow some kind of error message. Excellent suggestion, (behold the power of the command line!). I ran two saved versions of the script that had produced the symptom originally described. The fist seemed to be caused by too many 'if' statements, the second by adding another array, but both came up with the same system error at the command prompt level shown here: SystemError: com_backpatch: offset too large This error is not produced with the IDLE console but is seen only when executing from the command line. I'll search around and see if I can determine what this means and a possible fix. Thanks for the suggestion! Now we have seen the real error message it does appear as though this is an error in the interpreter triggered by an unusually long source program. See http://mail.python.org/pipermail/python-list/2004-November/249270.html for a previous discussion. In that email Diez Roggisch says: I can't believe that a program with 1 lines only adding strings can't be written in a more concise way, which would most probably solve your problem. So I suggest you post some parts of your code so that we can have a look at it and suggest a solution. The same applies here. Clearly it would be a good idea to remove whatever problem is causing the error, but in the meantime is there some way your code could be written more concisely? Or even split up into multiple modules? regards Steve -- Steve Holden +44 150 684 7255 +1 800 494 3119 Holden Web LLC www.holdenweb.com PyCon TX 2006 www.python.org/pycon/ -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
Steve Holden [EMAIL PROTECTED] wrote in message news:[EMAIL PROTECTED] Clearly it would be a good idea to remove whatever problem is causing the error, The problem (see my post of the com_backpatch code) is writing a compound statement (here a for loop) with a body so large as to require a jump of more than 64K bytes in the compiled bytecode (ie, from the test at the top of the loop to the code that follows after the loop). Until the jump limit is raised (likely a long wait ;-), the OP must factor some of the code out of the loop. Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
slogging_away wrote: Adding it back in cause it to not run - no error message - just a return to the in the IDLE console window much as if I had executed the 'Check Module' command. What happens if you run it from the command line instead of IDLE? After all, it might be some problem in IDLE involved here. Even if it doesn't work correctly outside IDLE, I was thinking that IDLE might swallow some kind of error message. -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
slogging_away wrote:
It appears it may not be a 'if' statment limitation at all. This is
because I added another 800 element array
Looks like a memory problem then...
in which to store the various
error messages generated when a configuration file error is deteceted
based on their severity level.
Why storing error messages ? Why don't you just write'em out (be it to
stdout or to a file) ?
(snip)
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Re: Too Many if Statements?
bruno at modulix wrote: Looks like a memory problem then... The system I am using has 2GB of memory, (unless you are syaing the memory is faulty). Why storing error messages ? Why don't you just write'em out (be it to stdout or to a file) ? I guess I could do that, (write them to a file as they are discovered). Right now the error messages are stored in the array and then the the array is scanned via, a for loop and the error messages are written to several files in different formats based on the severity of the errors, (on a per device basis, a per severity basis, etc.). This keeps the write statements to a minimum and in a central location of the script instead of having several statements for each individual error message spread throughout the script, (three write statements per error message at over 500 error messages would be a significant change). Not to complain but if I can't use arrays then thats a pretty significant limitation. -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
slogging_away wrote: bruno at modulix wrote: Why storing error messages ? Why don't you just write'em out (be it to stdout or to a file) ? I guess I could do that, (write them to a file as they are discovered). Right now the error messages are stored in the array and then the the array is scanned via, a for loop and the error messages are written to several files in different formats based on the severity of the errors, (on a per device basis, a per severity basis, etc.). This keeps the write statements to a minimum and in a central location of the script instead of having several statements for each individual error message spread throughout the script, (three write statements per error message at over 500 error messages would be a significant change). Sounds like you might like the logging module. A single log entry can be written to multiple destinations based on level or source of the entry. The distribution of log entries is controlled by the logging configuration which can be stored in a text file if you like. Kent -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
Magnus Lycka wrote: What happens if you run it from the command line instead of IDLE? After all, it might be some problem in IDLE involved here. Even if it doesn't work correctly outside IDLE, I was thinking that IDLE might swallow some kind of error message. Excellent suggestion, (behold the power of the command line!). I ran two saved versions of the script that had produced the symptom originally described. The fist seemed to be caused by too many 'if' statements, the second by adding another array, but both came up with the same system error at the command prompt level shown here: SystemError: com_backpatch: offset too large This error is not produced with the IDLE console but is seen only when executing from the command line. I'll search around and see if I can determine what this means and a possible fix. Thanks for the suggestion! -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
On Fri, 10 Feb 2006 06:50:25 -0800, slogging_away wrote: Excellent suggestion, (behold the power of the command line!). I ran two saved versions of the script that had produced the symptom originally described. The fist seemed to be caused by too many 'if' statements, the second by adding another array, but both came up with the same system error at the command prompt level shown here: SystemError: com_backpatch: offset too large Is this a Python error or a shell error? If it is a Python error, perhaps you would like to post the entire traceback? -- Steven. -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
Steven D'Aprano wrote: On Fri, 10 Feb 2006 06:50:25 -0800, slogging_away wrote: Excellent suggestion, (behold the power of the command line!). I ran two saved versions of the script that had produced the symptom originally described. The fist seemed to be caused by too many 'if' statements, the second by adding another array, but both came up with the same system error at the command prompt level shown here: SystemError: com_backpatch: offset too large Is this a Python error or a shell error? If it is a Python error, perhaps you would like to post the entire traceback? I would believe CamelCaseErrorMessages are produced by Python. The message is exactly the same I reported with the 2500 elifs. I fooled around a bit with this, and it seems that also for/while blocks containing more than ~4860 lines give this error. slogging_away claims his script is about 4900 lines, most of that in a for loop, so my bet is he has trouble with the same bug. -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
Terry Reedy wrote: 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??). Most of the if statements are nested. Almost all of them fall under a central 'for xxx in range(x,x,x)', (this is the statement that checks thorugh each of the saved configuration files). Under that 'for' statment are the bulk of the 'if' statements - some nested and some not - some also fall under other 'for' statements. The indent level does not exceed 10.. Delaney, Timothy (Tim) wrote: I'm pretty sure the OP has hit the python script line limit (32767?). The script is 4903 lines long. Slightly off topic; I am just a Network Engineer that can write some code that accomplishes what I need to get done. I'm learning something new everyday but I am really blown away by the responses to this thread. I could not buy support this good. Thanks for your responses. -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
Alan Morgan [EMAIL PROTECTED] wrote: In article [EMAIL PROTECTED], Bryan Olson [EMAIL PROTECTED] wrote: Alan Morgan wrote: slogging_away wrote: 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. I generated files with 1, 25000, and 5 simple if statements and ran them. 1 was okay, 25000 gave a bizarre internal error, and 5 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. 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. 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. Here[1] it works with 40 (with 50 it starts swapping too much) if-statements generated by == #!/usr/bin/env python print #!/usr/bin/env python zot=24999 for i in range(0, 40): print if zot == %d: print It's %d %(i,i) [1] Python 2.4.2 (#2, Sep 30 2005, 21:19:01) [GCC 4.0.2 20050808 (prerelease) (Ubuntu 4.0.1-4ubuntu8)] Florian -- No no no! In maths things are usually named after Euler, or the first person to discover them after Euler. [Steven D'Aprano in [EMAIL PROTECTED]] -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
slogging_away wrote: Terry Reedy wrote: 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??). Most of the if statements are nested. Almost all of them fall under a central 'for xxx in range(x,x,x)', (this is the statement that checks thorugh each of the saved configuration files). Under that 'for' statment are the bulk of the 'if' statements - some nested and some not - some also fall under other 'for' statements. The indent level does not exceed 10.. Has anyone considered that this may be part of the issue? If he is stepping through a range this is not just X if statements but n * x where n is the number of loops. Possibly some variables that are not getting freed between loops? (my guess would be that it is related to logging) Anyways, no expert here, just wanted to point that out. -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
Bryan Olson wrote:
Alan Morgan wrote:
slogging_away wrote:
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?
I generated files with 1, 25000, and 5 simple if statements
and ran
them. 1 was okay, 25000 gave a bizarre internal error, and 5
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.
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.
I tried that code. It runs fine.
However, the following gives a SystemError with only 2500 elif's.
#!/usr/bin/env python
lines = [ 'n = -1','m = 0','if n 0:',' m = 2*n',]
for i in range(2500):
lines.append('elif n == %i:' % i)
lines.append('m = 2*n')
prog = '\n'.join(lines)
progfile = file('if.py','w')
progfile.writelines(prog)
progfile.close()
exec prog
Traceback (most recent call last):
File iftest.py, line 10, in ?
exec prog
SystemError: com_backpatch: offset too large
I tried this with Python 2.3.3 and 2.3.4 (Linux) and both fail.
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Re: Too Many if Statements?
Pierre Quentel wrote:
This is because Python has a hidden mechanism to detect programs
generated by Perl scripts, and make them crash with no explanation
KEYBOARD !
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Re: Too Many if Statements?
bruno at modulix wrote:
[...]
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'another/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...).
If your checks are this complicated, I think you should consider
writing a parser for your configuration file. If you use a parser
generator it's not that difficult. Moreover a lexical analyzer could be
enough if your syntax is simple. I found Dave Beazley's PLY reasonably
easy to use: http://www.dabeaz.com/ply/
Cheers,
Nicola Musatti
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Re: Too Many if Statements?
In article [EMAIL PROTECTED], Pierre Quentel [EMAIL PROTECTED] wrote: This is because Python has a hidden mechanism to detect programs generated by Perl scripts, and make them crash with no explanation In my case it turned out to be python having a hidden method to detect when you are using an ancient version of python. Retesting with a newer version didn't find any problems. Alan -- Defendit numerus -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
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. I tried that code. It runs fine. However, the following gives a SystemError with only 2500 elif's. ... I tried this with Python 2.3.3 and 2.3.4 (Linux) and both fail. Just tried it with 2.4.2 On FreeBSD 6.0 and I get the same result: Traceback (most recent call last): File buggyif.py, line 10, in ? exec prog SystemError: com_backpatch: offset too large Curtis -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
[EMAIL PROTECTED] [EMAIL PROTECTED] writes: SystemError: com_backpatch: offset too large Yeah, that sounds like there's some 16-bit fields in the bytecode format. -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
Juho Schultz wrote: However, the following gives a SystemError with only 2500 elif's. SystemErrors should never occur, if you see one it's a bug. [valid program which demonstrates a python bug] Traceback (most recent call last): File iftest.py, line 10, in ? exec prog SystemError: com_backpatch: offset too large I tried this with Python 2.3.3 and 2.3.4 (Linux) and both fail. Yup, 2.4 fails too. Unfortunately, this looks like a bugger to fix in 2.4. So I doubt it will be fixed for old versions of python. The good news is that it's fixed for 2.5. n -- http://mail.python.org/mailman/listinfo/python-list
Too Many if Statements?
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? -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
slogging_away wrote:
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?
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 ?
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p in '[EMAIL PROTECTED]'.split('@')])
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Re: Too Many if Statements?
slogging_away wrote: 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? 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...something 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 -- http://mail.python.org/mailman/listinfo/python-list
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! -- http://mail.python.org/mailman/listinfo/python-list
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. -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
slogging_away wrote:
I don't consider myself to be a seasoned programmer
nor do I.
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.
I strongly doubt it could *not* 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.
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.
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.
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'another/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...).
I appreciate the feedback though!
You're welcome !-)
--
bruno desthuilliers
python -c print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
p in '[EMAIL PROTECTED]'.split('@')])
--
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Re: Too Many if Statements?
In article [EMAIL PROTECTED], slogging_away [EMAIL PROTECTED] wrote: 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? I generated files with 1, 25000, and 5 simple if statements and ran them. 1 was okay, 25000 gave a bizarre internal error, and 5 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 -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
Try the state(s) pattern! slogging_away [EMAIL PROTECTED] wrote: 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? -- Regards, Casey -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
Alan Morgan wrote:
slogging_away wrote:
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?
I generated files with 1, 25000, and 5 simple if statements and ran
them. 1 was okay, 25000 gave a bizarre internal error, and 5
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.
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.randrange(10L**10)
]
for i in range(10):
lines.append('if n % random.randrange(2, 1000) == 0: c += 1')
lines.append('print c')
lines.append('##')
progtext = '\n'.join(lines)
f = file('manyifs.py', 'w')
f.write(progtext)
f.close()
exec progtext
--
--Bryan
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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! -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
Bryan Olson [EMAIL PROTECTED] wrote in message news:[EMAIL PROTECTED] 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. 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 -- http://mail.python.org/mailman/listinfo/python-list
RE: Too Many if Statements?
Terry Reedy wrote: 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??). I'm pretty sure the OP has hit the python script line limit (32767?). Goggle searches haven't turned up the actual limit for me unfortunately. I suppose I could go check the code ... Tim Delaney -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
In article [EMAIL PROTECTED], Bryan Olson [EMAIL PROTECTED] wrote: Alan Morgan wrote: slogging_away wrote: 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. I generated files with 1, 25000, and 5 simple if statements and ran them. 1 was okay, 25000 gave a bizarre internal error, and 5 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. 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. 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 -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
Terry Reedy wrote: Bryan Olson wrote: 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. 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??). 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 -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
slogging_away wrote: 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) Have you tried xrange() instead of range()? 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! -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
Alan Morgan wrote: 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. Everyone, Please file a bug report anytime you make Python crash! http://sourceforge.net/tracker/?group_id=5470atid=105470 If you aren't willing to deal with SF, at least send me source code (not a description) that makes python crash. n -- http://mail.python.org/mailman/listinfo/python-list
Re: Too Many if Statements?
This is because Python has a hidden mechanism to detect programs generated by Perl scripts, and make them crash with no explanation Pierre -- http://mail.python.org/mailman/listinfo/python-list
