Re: my recursive function call is wrong?

[Chang Min Jeon]

Dear Kev

Thank you very much.
I got it.:)

2009/8/16 Kev Dwyer 

> On Sun, 16 Aug 2009 16:57:41 +0900, Chang Min Jeon wrote:
>
>
> Hello,
>
> You have placed recursive calls to the function in a number of different
> locations; when len(macro) becomes zero control will return to the
> calling function, but this calling function may have more code to
> execute, including further calls to start_parse(), and further attempts
> to index macro.
>
> I like to keep recursive calls at the end of a function, so that there is
> a clean path back to the top level caller once the terminal condition is
> reached.  You can do it differently, but you need to bear in mind the
> execution paths through your code.
>
> Cheers,
>
> Kev
>
> --
> http://mail.python.org/mailman/listinfo/python-list
>



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Re: my recursive function call is wrong?

[Kev Dwyer]

On Sun, 16 Aug 2009 16:57:41 +0900, Chang Min Jeon wrote:


Hello,

You have placed recursive calls to the function in a number of different 
locations; when len(macro) becomes zero control will return to the 
calling function, but this calling function may have more code to 
execute, including further calls to start_parse(), and further attempts 
to index macro.

I like to keep recursive calls at the end of a function, so that there is 
a clean path back to the top level caller once the terminal condition is 
reached.  You can do it differently, but you need to bear in mind the 
execution paths through your code.

Cheers,

Kev

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my recursive function call is wrong?

[Chang Min Jeon]

I'm trying to write program to translate define macro in 'C'.
And start_parse has return condition that list's length is 0.
At this time return statement invoke start_parse() function.
I can't understand do that.

I'm using Python 2.6.2 in Windows XP

import re
import sys
comment = '''
#if defined (FEATURE_ONENESTED)
#define PYTHON_POWERED
#if defined(ANY_LANGUAGE)
#error
#endif
#else
#define FEATURE_NONE
#endif
'''

symbol_table = ['FEATURE_ONENESTED']

valid_area = False

p_define = re.compile('^[\t ]*#[\t ]*define[\t ]+([a-zA-Z0-9_]+)[\t ]*')
p_if = re.compile('^[\t ]*#[\t ]*if[\t
]+defined[\s]*[\(]*([a-zA-Z0-9_]+)[\)]*[\t ]*')
p_elif = re.compile('^[\t ]*#[\t ]*elif[\t ]*')
p_else = re.compile('^[\t ]*#[\t ]*else[\t ]*')
p_endif = re.compile('^[\t ]*#[\t ]*endif[\t ]*')

def start_parse(macro):
global valid_area
if len(macro) == 0:
return

if valid_area == True:

if p_else.match(macro[0]):
valid_area = False
macro.pop(0)
start_parse(macro)

match = p_define.match(macro[0])
if match:
symbol_table.append(match.group(1))
macro.pop(0)
start_parse(macro)


match = p_if.match(macro[0])
if match:
for symbol in symbol_table:#print match.group(1)
if match.group(1) == symbol:
#print match.group(1)
valid_area = True
else:
valid_area = False

if p_else.match(macro[0]):
macro.pop(0)
start_parse(macro)

match = p_endif.match(macro[0])
if match:
valid_area = False

macro.pop(0)
start_parse(macro)

if __name__ == '__main__':
l = comment.splitlines()
start_parse(l)
print symbol_table
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