Using Regex In Python To Find Substring?

Question

I have A string:

line_to_test = "http://website/[SequenceOfLetters&NumbersONLY].html"

I want a regex for matching the above pattern:

what i have tried currently is:

c = len(re.findall(r"http:\/\/website\/([a-zA-Z0-9]?).html",line_to_test))

But c here comes to be null even when the line_to_test contains the pattern.

([a-zA-Z0-9]?) = 1 or 0 letter or number - if you want a sequence, you want to replace ? with +... — Keith Hall
– Keith Hall, Commented Mar 24, 2016 at 10:28
test_string = "sdfmknldksjfnkmsd f,nm http://abc.de/msndkjnaskl.html" — CodeAllDay
– CodeAllDay, Commented Mar 24, 2016 at 10:28

Kaspar Lee · Accepted Answer · 2016-03-24 10:36:07Z

2

? means whatever preceded it was optional, in this case [a-zA-Z0-9]. That means you can have a letter or number either 0 or 1 times.

You should use the *, to select it 0 times or more, or use the +, to select it 1 times` or more.

Try this RegEx:

c = len(re.findall(r"http:\/\/website\/([a-zA-Z0-9]+).html",line_to_test))

If you used a *, it would be the same as ([a-zA-Z0-9]+)?, meaning http://website/.html would work.

answered Mar 24, 2016 at 10:36

Kaspar Lee

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1 Comment

Thanks For the precise explaination !!

Selcuk · Accepted Answer · 2016-03-24 10:28:00Z

0

? will only match 0 or 1 character. Try

c = len(re.findall(r"http:\/\/website\/([a-zA-Z0-9]+).html",line_to_test))

You can use an online service like regexr to test your regexes: http://regexr.com/3d301

answered Mar 24, 2016 at 10:28

Selcuk

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