Replacing multiple items with regex in Python

Question

I have a text file that contains certain string sequences that I want to modify. For example, in the following string I would like to replace foo and bar each with a unique string (The new string will be based on what originally matches, so I won't know it before hand).

Original: foo text text bar text
Replaced: fooNew text text bar_replaced text

I am using regex to find the groups that I need to change based on how they are delimited in the actual text. If I just use re.findAll(), I no longer have the location of the words in the string to reconstruct the string after modifying the matched groups.

Is there a way to preserve the location of the words in the string while modifying each match separately?

Right after posting this I realized I could probably use str.replace() after re.findAll(), but since I have already typed it out I wonder if anyone has a better way. — digitaLink
– digitaLink, Commented Aug 4, 2017 at 14:39
If the search strings are hardcode strings and there is no context to account for when matching the strings, use chained replace methods. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Aug 4, 2017 at 14:41
@asongtoruin What I will substitute depends on what I find during matching. I can't know what to substitute ahead of time. — digitaLink
– digitaLink, Commented Aug 4, 2017 at 14:46

cs95 · Accepted Answer · 2017-08-04 14:43:25Z

2

Option 1

I would recommend this for complicated scenarios. Here's a solution with re.sub and a lambda callback:

In [1]: re.sub('foo|bar', lambda x: 'fooNew' if x.group() == 'foo' else 'bar_replaced', text)
Out[1]: 'fooNew text text bar_replaced text'

Option 2

Much simpler, if you have hardcoded strings, the replacement is possible with str.replace:

In [2]: text.replace('foo', 'fooNew').replace('bar', 'bar_replaced')
Out[2]: 'fooNew text text bar_replaced text'

answered Aug 4, 2017 at 14:43

cs95

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2 Comments

digitaLink Over a year ago

In "Option 1" can any function go after lambda x: for the new replacement?

cs95 Over a year ago

@digitaLink Exactly.

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