Python Text substitute

Applications Programming
1

I need to substitute only comma with dot in string like this:

<strong>5,4</strong>

but not sure how to do this.
This does not work:

text = sub('<strong>[0-9](,)[0-9]</strong>', '<strong>[0-9](.)[0-9]</strong>', text)
2 
>>> text = "<strong>5,4</strong>"
>>> text = text.replace(',', '.')
>>> text
'<strong>5.4</strong>'