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Python

Posted by Mike Brooks
Mike Brooks
3,389 Points

Python: Using variables in regular expression meta-characters{}

In one of the regular expression checks I was trying to do the following:

def find_words(count, myString):
    print(myString)
    return re.findall("\w{count,}", myString)

to find words with a count or more number of letters in myString

It came back with an empty list. I googled trying to put variables in metacharacters but all the examples were numeric.

I got it to work using the following:

def find_words(count, myString):
    print(myString)
    return re.findall(("\\w{" + str(count) + ",}"), myString)

BUT I am assuming there is a much more elegant way to do this.

Any help appreciated.

1 Answer

Stuart Wright
Stuart Wright
41,120 Points

I'm not an expert at regex, and I wouldn't necessarily say this is more elegant than your solution, but it's at least an alternative:

def find_words(count, myString):
    print(myString)
    return re.findall(r"\w{{{},}}".format(count), myString)

It uses string formatting rather than the concatenation technique you used.

Note that the double braces which form the {m, n} part of the string have their curly braces doubled. This is necessary to distinguish them from the {} placeholder required for the string formatting.