How can I replace all occurrences of a substring using regex?

I have a string, s = 'sdfjoiweng%@$foo$fsoifjoi', and I would like to replace 'foo' with 'bar'.

I tried re.sub(r'\bfoo\b', 'bar', s) and re.sub(r'[foo]', 'bar', s), but it doesn't do anything. What am I doing wrong?

4 Answers

You can replace it directly:

>>> import re >>> s = 'sdfjoiweng%@$foo$fsoifjoi' >>> print(re.sub('foo','bar',s)) sdfjoiweng%@$bar$fsoifjoi 

It will also work for more occurrences of foo like below:

>>> s = 'sdfjoiweng%@$foo$fsoifoojoi' >>> print(re.sub('foo','bar',s)) sdfjoiweng%@$bar$fsoibarjoi 

If you want to replace only the 1st occurrence of foo and not all the foo occurrences in the string then alecxe's answer does exactly that.

re.sub(r'\bfoo\b', 'bar', s)

Here, the \b defines the word boundaries - positions between a word character (\w) and a non-word character - exactly what you have matching for foo inside the sdfjoiweng%@$foo$fsoifjoi string. Works for me:

In [1]: import re In [2]: s = 'sdfjoiweng%@$foo$fsoifjoi' In [3]: re.sub(r'\bfoo\b', 'bar', s) Out[3]: 'sdfjoiweng%@$bar$fsoifjoi' 

You can use replace function directly instead of using regex.

>>> s = 'sdfjoiweng%@$foo$fsoifjoifoo' >>> >>> s.replace("foo","bar") 'sdfjoiweng%@$bar$fsoifjoibar' >>> >>> 

To further add to the above, the code below shows you how to replace multiple words at once! I've used this to replace 165,000 words in 1 step!!

Note \b means no sub string matching..must be a whole word..if you remove it then it will make sub-string match.

import re s = 'thisis a test' re.sub('\bthis\b|test','',s) 

This gives:

'thisis a '