Replacing first whitespace in every line with a comma [closed]

Question

I need to perform this operation to every single line in a text file and then write it to another file. I need to remove the first whitespace and replace it with a comma (,).

However, I don't want this to happen to any other whitespace on the line. Here is a snippet from the input text file:

Achilles Patroclus
Achilles Triumph of Achilles in Corfu Achilleion
Achilles Antilochus
Achilles Hephaestus
Achilles Shield of Achilles

Answer 1

You can do something like this:

[",".join(line.split(" ", 1)) for line in lines]

Answer 2

Using re.sub with ^([^\s]*)\s+:

>>> s
'Achilles Triumph of Achilles in Corfu Achilleion'

>>> re.sub(r'^([^\s]*)\s+', r'\1, ', s)
'Achilles, Triumph of Achilles in Corfu Achilleion'