Checking whether a string contains some characters in python

Question

I want to check if a string only contains A-Z and a-z and 0-9 and underscore and dash (_ -)

Any other special signs like !"#\% should not be contained

How can I write the regular expression?

and use match or ?

My strings look like these: QOIWU_W QWLJ2-1

Answer 1

Yes, re.match seems like a good match (pardon the pun). As for the regular expression, how about something like this: '[A-Za-z0-9-_]*'?

Answer 2

Using re doesn't harm in any way, but just for scientific curiosity, another approach that doesn't require you to pass through re is using sets:

>>> valid = set('ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_ ')
>>> def test(s):
...    return set(s).issubset(valid)
... 
>>> test('ThiS iS 4n example_sentence that should-pass')
True
>>> test('ThiS iS 4n example_sentence that should fail!!')
False

For conciseness, the testing function could also be written:

>>> def test(s):
...    return set(s) <= valid

EDIT: A bit of timing for the sake of curiosity (times are in seconds, for each test implementation it runs three sets of iterations):

>>> T(lambda : re.match(r'^[a-zA-Z0-9-_]*$', s)).repeat()
[1.8856699466705322, 1.8666279315948486, 1.8670001029968262]
>>> T(lambda : set(y) <= valid).repeat()
[3.595816135406494, 3.568570852279663, 3.564558982849121]
>>> T(lambda : all([c in valid for c in y])).repeat()
[6.224508047103882, 6.2116711139678955, 6.209425926208496]