Regular Expression question

Fredrik Lundh fredrik at pythonware.com
Thu Dec 1 19:09:06 CET 2005


Michelle McCall wrote:

>I have a script that needs to scan every line of a file for numerous
> strings.  There are groups of strings for each "area" of data we are looking
> for.  Looping through each of these list of strings separately for each line
> has slowed execution to a crawl.  Can I create ONE regular expression from a
> group of strings such that when I perform a search on a line from the file
> with this RE it will search the line for each one of the strings in the RE ?

does

    m = re.search("spam|egg|bacon", line)

do what you want?

if you need all matches, you can use

    for m in re.finditer("spam|egg|bacon", line):
        ...

if the strings are all literal strings (i.e. no subpatterns), a little preparation might
speed things up:

    words = ["spam", "spim", "spum", "spamwall", "wallspam"]
    words.sort() # lexical order
    words.reverse() # look for longest match first
    pattern = "|".join(map(re.escape, words))
    pattern = re.compile(pattern)

    for m in pattern.finditer(line):
        ...

</F> 






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