What is the recommended way to replace multiple lines in one large line in Python?

Question

I have many pairs of lines and one large line (this is the contents of the file). I need to replace each occurrence of the first member in each pair with the corresponding second.

For example, having the pairs ("AA", "BB") and ("qq", "rt"), I need to replace each occurrence of AA with BB and qq with rt .

Lines in pairs are unique, so the order of replacement does not matter in the final result.

My python code is the most naive - I use the string.replace method sequentially until all the pairs are exhausted:

>>> s="frsfsdAAsdfvsdfvqqdsff" >>> pairs=[('AA', 'BB'), ('qq', 'rt')] >>> for p in pairs: ... s=s.replace(p[0], p[1]) ... >>> s 'frsfsdBBsdfvsdfvrtdsff' >>> 

I believe this is a bad solution for large strings. Can anyone suggest a more efficient one?

The question is how to do this in Python.

Thanks.

Answer 1

Something else is wrong with your proposed solution: after the first replacement is completed, the final line may match, and the same characters can be replaced again. For example, your solution will not give the desired result if you try to change 'qq' and 'ff' by setting pairs = [('qq','ff'), ('ff','qq')] .

Instead, you can try:

 >>> d = dict(pairs) >>> import re >>> pattern = re.compile('|'.join(re.escape(k) for k in d)) >>> pattern.sub(lambda k:d[k.group()], s)) frsfsdBBsdfvsdfvrtdsff