Iteration within re.sub()?

[Bryant Huang]

Hi,

Is it possible to perform iteration within the re.sub() function call?

For example, if I have a string like:

str = "abbababbabbaaa"

and I want to replace all b's with an integer that increments from 0,
could I do that with re.sub()?

Replacing b's with 0's is trivial:

i = 0
pat = re.compile("b")
print pat.sub(`i`, str)

Now, how can I increment i in each replacement? Is this possible? Like,
using a lambda function, for example? Or do I use a different re
function altogether?

I use this trivial [ab]* language for simplicity, but I have a real
problem where I need to match a more complex regex and replace it with
an incrementing integer.

Thanks so much!
Bryant

[Mark McEahern]

Bryant Huang wrote:

Hi,

Is it possible to perform iteration within the re.sub() function call?

Sure. As the docs note:

If repl is a function, it is called for every non-overlapping occurrence
of pattern. The function takes a single match object argument, and
returns the replacement string. For example:

#!/usr/bin/env python

import re

class Counter:
def __init__(self):
self.count = -1
def increment(self, matchObject):
self.count += 1
return str(self.count)

text = "abbababbaaaaaabbaaa"
expected = "a01a2a34aaaaaa56aaa"

# Replace all b's with an integer that increments from 0.

c = Counter()
pat = re.compile("(b)")
actual = pat.sub(c.increment, text)
assert expected == actual

[Bryant Huang]

Ah beautiful, thank you both, Robert and Mark, for your instant and
helpful responses. I understand, so the basic idea is to keep a
variable that is globally accessible and call an external function to
increment that variable...

Thanks!
Bryant

[Fredrik Lundh]

Bryant Huang wrote:

Ah beautiful, thank you both, Robert and Mark, for your instant and
helpful responses. I understand, so the basic idea is to keep a
variable that is globally accessible and call an external function to
increment that variable...

accessible for the callback function, that is.

see Mark's example for the right way to do it (using a object to hold
the state, and an object method as the callback -- the latter is known
as a "bound method", and holds a reference to both the data (self) and
the code).

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