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

Question

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?

Answer 1

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.

Answer 2

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'