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
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-_]*'?
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-_]*$', s)).repeat()
[1.8856699466705322, 1.8666279315948486, 1.8670001029968262]
>>> T(lambda : set(y) <= valid).repeat()
[3.595816135406494, 3.568570852279663, 3.564558982849121]
>>> T(lambda : all([c in valid for c in y])).repeat()
[6.224508047103882, 6.2116711139678955, 6.209425926208496]
list calls to get the sets of characters.
You can use the regular expression module.
import re
if (re.match('^[a-zA-Z0-9-_]*$',testString)):
//successful match
No need to go regexp.
import string
# build a string containing all valid characters
match=string.ascii_letters + string.digits + '_' + '-' + ' '
In [25]: match
Out[25]: 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_- '
test='QOIWU_W QWLJ2-'
In [22]: all([c in match for c in test])
Out[22]: True
In [23]: test2='abc ;'
In [24]: all([c in match for c in test2])
Out[24]: False
in is linear with the length of the search string so it wasn't a major surprise. Thanks for the benchmark though!import re
re.search('[^a-zA-Z0-9-_]+', your_string) == None
re.search() will return a match object if it comes across any instances of one or more non-alphanumeric characters and None otherwise. So you'd be checking if the string is safe.
