Python Regex pattern not being matched

Question

I'm trying to get some regex to parse some values stored in a set of lua files, each line looks something like one of these two lines

ITEM.ID = 'item_clock';\r\n
ITEM.Cost = 150;\r\n.

when I run my regex pattern on the first line I get an expected result

>>> re.search("ITEM.(?P<key>[a-zA-Z]\w) = (?P<value>.*);", line).groupdict()
{'key': 'ID', 'value': "'item_clock'"}

however when I run it on the second line, I don't get a Match object.

NPE · Accepted Answer · 2011-10-13 12:43:15Z

7

The regex looks for ITEM. followed by a letter then followed by exactly one word character (the \w in the regex).

You probably meant something like ITEM.(?P<key>[a-zA-Z]\w*)... (note the added asterisk). This will look for ITEM. followed by a letter then followed by zero or more word characters.

Also, it's a good idea to use raw strings for regular expressions to avoid hard-to-spot bugs:

r"ITEM.(?P<key>[a-zA-Z]\w*) = (?P<value>.*);"

(note the r prefix).

edited Oct 13, 2011 at 12:43

answered Oct 13, 2011 at 12:38

NPE

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3 Comments

H4Z3Y Over a year ago

thanks, that has worked perfectly! I'm just starting to get my head around regex.

NPE Over a year ago

@H4Z3Y: I've just added a note about raw strings. I think it's a good habit to get into.

andronikus Over a year ago

+1 for raw strings. This is such a good idea that python should really just enforce it, since that seems to be a big part of their design philosophy anyway.

Phil Cooper · Accepted Answer · 2011-10-13 13:49:16Z

1

Accepted answer is right. Minor tweaks...

escape the "." after ITEM to mean a "." and not just anything
usually a good idea to allow for more than one space (or no spaces) around the "="

r"ITEM\.(?P<key>[a-zA-Z]\w*) *= *(?P<value>.*?) *;"

edited Oct 13, 2011 at 13:49

answered Oct 13, 2011 at 13:41

Phil Cooper

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3 Comments

heltonbiker Over a year ago

I think escaping the spaces just as you did with the dot is a good idea too.

Phil Cooper Over a year ago

Agreed the best is to replace the " *" with "\s*" ... better regex but a little less readable ... like regex is ever readable

heltonbiker Over a year ago

Actually I meant \ (with the space character), but I think in the end there is indeed a lot of "space" (pun intended) for personal preference ;o). So it would become r"ITEM\.(?P<key>[a-zA-Z]\w*)\ *=\ *(?P<value>.*?) *;" (formatting removed one space :o(

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