CODEWITHSUNDEEP
pythonregex
Harsh Sharma
Harsh Sharma

Reputation: 11232

Regular expression search not working when changing the order of pattern

I am just writing a small regex to filter email from string. When I am using pattern as patt = r'[\w.-]+@[\w.-]+', it's working fine. But when I am using pattern as patt1 = r'[\w-.]+@[\w-.]+', its giving me error:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/re.py", line 146, in search
    return _compile(pattern, flags).search(string)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/re.py", line 251, in _compile
    raise error, v # invalid expression
sre_constants.error: bad character range

Code:

1st case:

>>> str = "[email protected]"
>>> patt = r'[\w.-]+@[\w.-]+'
>>> match = re.search(patt, str)
>>> match.group()
'[email protected]'

2nd case:

>>> str = "[email protected]"
>>> patt = r'[\w-.]+@[\w-.]+'
>>> match = re.search(patt, str)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/re.py", line 146, in search
    return _compile(pattern, flags).search(string)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/re.py", line 251, in _compile
    raise error, v # invalid expression
sre_constants.error: bad character range

Any idea what I am doing wrong in the second regex?

Upvotes: 3

Views: 449

Answers (2)

heemayl
heemayl

Reputation: 41987

The dash (-) inside a character class ([]) indicates a character range i.e. from-to. So, if you want to use literal -, you have 3 options:

  • put - at the start: [-foo]
  • put - at the end: [foo-]
  • escape - with \: [foo\-bar]

Upvotes: 1

Nick
Nick

Reputation: 7431

Hyphens - need to be the first or last in the list. They have special meaning when used between two characters to indicate a range, like [A-Z] (all uppercase letters). When a hyphen is at the end or beginning, it has not special meaning.

Also, escaping it \- will work in Python, but beware it may not in other implementations/languages.

Check out the accepted answer here: Regex - Should hyphens be escaped?

Not the exact same question as yours, but touches on similar information.

Upvotes: 2

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