Python regex, pulling patterns out of a match and using them as input back into the match

Question

I have searched for an answer. I am sure they are out there, but there are way too many false hits.

This is my script (my attempt fails):

#!/bin/env python

import re

usage="""
    My favorite restaurant is <<<res>>>
    My favorite person is <<<per>>>
"""

res="pizza hut"
per="my sister"

def main():
    value = re.sub(r'<<<(\w+)>>>', globals()[r'\1'], usage)
    print 'value=%s.' % (value)

if ( __name__ == "__main__"):
    main()

What I am trying to output is:

value=
    My favorite restaurant is pizza hut
    My favorite person is my sister
.

The closest answer that I have seen, involves maintaining a separate list. I do not want to have to maintain a separate list.

Why are you using globals() here? There is no global name \1 in your code (nor could there be). — Martijn Pieters
– Martijn Pieters, Commented Nov 7, 2013 at 17:01

Andrew Clark · Accepted Answer · 2013-11-07 16:58:38Z

2

You can use a function as the replacement in re.sub(). The function will receive the match object as the only argument and should return a string. The best way to do this is to create a dictionary with your replacements:

import re

usage="""
    My favorite restaurant is <<<res>>>
    My favorite person is <<<per>>>
"""

rep = {"res": "pizza hut",
       "per": "my sister"}

print re.sub(r'<<<(\w+)>>>', lambda m: rep.get(m.group(1), ""), usage)

You could use this exact same method with globals(), but using globals() in this way is generally discouraged when a dictionary offers the same behavior in a safer way.

answered Nov 7, 2013 at 16:58

Andrew Clark

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2 Comments

Joran Beasley Over a year ago

ahhh you beat me :P by alot ... how did I not see this (+1)

cforbish Over a year ago

Thanks for the answer. I tried it and it worked, so I gave you an upvote!

Ashwini Chaudhary · Accepted Answer · 2013-11-07 17:00:06Z

2

Use a dict instead of using variables, and change <<<res>>> to {res} using regex so that you can use string formatting on it:

>>> import re
>>> usage="""                                   
    My favorite restaurant is <<<res>>>
    My favorite person is <<<per>>>
"""
>>> my_dict = {'res':'pizza hut', 'per':'my sister'}
>>> print re.sub(r'<<<(\w+)>>>', r'{\1}', usage).format(**my_dict)

    My favorite restaurant is pizza hut
    My favorite person is my sister

answered Nov 7, 2013 at 17:00

Ashwini Chaudhary

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Comments

score 1 · Accepted Answer · 2013-11-07 17:32:53Z

1

This is a dangerous way using eval:

def repl(match):
    return eval(match.group(0)[3:-3])

print re.sub(r'<<<\w+>>>', repl, usage)

Output:

My favorite restaurant is pizza hut
My favorite person is my sister

edited Nov 7, 2013 at 17:32

answered Nov 7, 2013 at 17:14

user1301404

3 Comments

Simeon Visser Over a year ago

Wait, out of all the answers you choose the one with eval()?

user1301404 Over a year ago

The closest answer that I have seen, involves maintaining a separate list. I do not want to have to maintain a separate list.

I gave the solution without using a separate list or dict.

cforbish Over a year ago

Yes this is the closest to what I wanted.

Simeon Visser · Accepted Answer · 2013-11-07 16:59:04Z

1

Are you free to modify the formatting? Python already supports this by doing:

usage = """
    My favorite restaurant is {res}
    My favorite person is {per}
"""
res = "pizza hut"
per = "my sister"

print usage.format(**globals())

answered Nov 7, 2013 at 16:59

Simeon Visser

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2 Comments

cforbish Over a year ago

Thanks for the answer. I tried it and it worked, so I gave you an upvote!

cforbish Over a year ago

I do not know that my final usage string might need to have a "{some stuff}" pattern in it that is not a intended for replacement. Because of this I might have to change the replacement pattern to insure all are intended to be replaced by variable values. I want to be able to change this (i.e. to __VAR(???)__, instead of <<<???>>>).

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