Python re.sub question

Question

Greetings all,

I'm not sure if this is possible but I'd like to use matched groups in a regex substitution to call variables.

a = 'foo'
b = 'bar'

text = 'find a replacement for me [[:a:]] and [[:b:]]'

desired_output = 'find a replacement for me foo and bar'

re.sub('\[\[:(.+):\]\]',group(1),text) #is not valid
re.sub('\[\[:(.+):\]\]','\1',text) #replaces the value with 'a' or 'b', not var value

thoughts?

Answer 1

You can specify a callback when using re.sub, which has access to the groups: http://docs.python.org/library/re.html#text-munging

a = 'foo'
b = 'bar'

text = 'find a replacement for me [[:a:]] and [[:b:]]'

desired_output = 'find a replacement for me foo and bar'

def repl(m):
    contents = m.group(1)
    if contents == 'a':
        return a
    if contents == 'b':
        return b

print re.sub('\[\[:(.+?):\]\]', repl, text)

Also notice the extra ? in the regular expression. You want non-greedy matching here.

I understand this is just sample code to illustrate a concept, but for the example you gave, simple string formatting is better.