Why doesn't the regex match when I add groups?

Question

I have this regex code in python :

if re.search(r"\{\\fad|fade\(\d{1,4},\d{1,4}\)\}", text):
  print(re.search(r"\{\\fad|fade\((\d{1,4}),(\d{1,4})\)\}", text).groups())

text is {\fad(200,200)}Épisode 101 : {\i1}The Ghost{\i0}\Nv. 1.03 and read from a file (don't know if that helps).

This returns the following:

(None, None)

When I change the regex in the print to r"\{\\fad\((\d{1,4}),(\d{1,4})\)\}", it returns the correct values:

(200, 200)

Can anyone see why the conditional fad|fade matches the regex in the re.search but doesn't return the correct values of the groups in the print?

Thanks.

Answer 1

I think your conditional is looking for "\fad" or "fade", I think you need to move a \ outside the grouping if you want to look for "\fad" or "\fade".

Answer 2

Try this:

r"\{\\fade?\(\d{1,4},\d{1,4}\)\}"

Answer 3

The bracket is part of the or branch starting with fade, so it's looking for either "{fad" or "fade(...". You need to group the fad|fade part together. Try:

r"\{\\(?:fad|fade)\(\d{1,4},\d{1,4}\)\}"

[Edit] The reason you do get into the if block is because the regex is matching, but only because it detects it starts with "{\fad". However, that part of the match contains no groups. You need to match with the part that defines the groups if you want to capture them.

Answer 4

Put extra parens around the choice: re.search(r"{(?:\\fad|fade)\((\d{1,4}),(\d{1,4})\)}", text).groups()

Also, escaping {} braces isn't necessary, it just needlessly clutters your regexp.

Answer 5

I don't know the python dialect of regular expressions, but wouldn't you need to 'group' the "fad|fade" somehow to make sure it isn't trying to find "fad OR fade(etc..."?

Answer 6

Try this instead:

r"\{\\fade?\((\d{1,4}),(\d{1,4})\)\}"

The e? is an optional e. The way you have it now matches {\fad or fade(0000,0000)}