regex (vim) for print ... to print(...) for python2 to python3

Question

This post is helpful only if you have strings inside of the print command. Now I have tons of sourcecode with a statement such as

print milk,butter

which should be formatted to

print(milk,butter)

And capturing the end of the line with \n was not sucessfull. Any hints?

Answer 1

I am not familiar with 2to3, but from all the comments, it looks like the correct tool for the job.

That said, perhaps we can use this question as an excuse for a short lesson in some vim basics.

First, you want a pattern that matches the correct lines. I think that ^\s*print\> will do:

• ^ matches start of line (and $ matches end of line).
• \s matches whitespace (space or tab)
• * means 0 or more of the previous atom (as many as possible, or "greedy").
• print is a literal string.
• \> matches end-of-word (zero width). You might use a (literal) space or \s\+ instead.

Next, you need to identify the part to be enclosed in parentheses. Since * is greedy, .* will match to the end of the line; there is no need to anchor it on the right. Use \(\s*print\) and \(.*\) to capture the pieces, so that you can refer to them as \1 and \2 in the replacement.

Now, put the pieces together. There are many variants, and I have not tried to "golf" this one:

:%s/^\(\s*print\)\s\+\(.*\)/\1(\2)

Some people prefer the "very magic" version, where only a-z, A-Z, 0-9, and _ are treated as literal characters; then you do not need to escape the parentheses nor the plus:

:%s/^\v(\s*print)\s+(.*)/\1(\2)

Answer 2

You could use 2to3 and only apply the fix for print statement -> print function.

2to3 --fix=print [yourfiles]

This should automatically handle all those strange cases which won't work with e.g. a vim regex.

If you are missing the 2to3 shell script for some reason, run the lib as a module:

python -m lib2to3 --fix=print [yourfiles]

Answer 3

Since you're in vim already:

:!2to3 --fix=print --write %