Why doesn't this regexp match?

I am using python, and this regexp doesn't match, and I don't understand why.

string = "15++12"
if re.match("[-+*/][-+*/]+",string):
    # raise 开发者_如何学编程an error here

I am trying to raise an error, if one or more of "-","+","*","/" follows another one of those.

Use re.search() as re.match() only searches at the beginning of the string:

string = "15++12"
if re.search("[-+*/][-+*/]+",string):
    # raise an error here

Also, this could be simplified to:

string = "15++12"
if re.search("[-+*/]{2,}",string):
    # raise an error here

as the {2,} operator searches for two or more of the previous class.

re.match tries to match from the beginning of the string. To match any substring, either use re.search or put a .* before the pattern:

>>> re.match("[-+*/][-+*/]+", s)
>>> re.search("[-+*/][-+*/]+", s)
<_sre.SRE_Match object at 0x7f5639474780>
>>> re.match(".*[-+*/][-+*/]+", '15++12')
<_sre.SRE_Match object at 0x7f5639404c60>

I believe it is because re.match matches only the beginning of the string. Try re.search or re.findall

Check out 7.2.2 at python docs: http://docs.python.org/library/re.html

Python violates the Principle of Least Surprise here: they've chosen a word with an established meaning and warped it into meaning something different from that. This isn't quite evil and wrong, but it is certainly stupid and wrong. – tchrist @tchrist

I don't agree. In fact, I think exactly the contrary, it isn't stupid

If I say :

a regex's pattern "\d+[abc]" matches the string '145caba'

everybody will agree with this assertion.

If I say :

a regex's pattern "\d+[abc]" matches the string 'ref/ 789lomono 145abaca ubulutatouti'

80 % of people will agree and the other rigorous 20 % of people, in which I am, will be unsatisfied by the wording and will reclaim that the expression be changed to :

"\d+[abc]" matches SOMEWHERE in the string 'ref/ 789lomono 145abaca ubulutatouti'

That's why I find justified to call an action that consists to search if and where a pattern matches in a string: search()

and to call the action to verify if a match occurs from the beginning: match()

For me it's very much logical, not surprising

.

PS

A former answer of mine have been deleted. As I don't know how to write to the author of the deletion to ask him the reason why he judged my former answer being a rant (!!!?), I re-post what seems to me absolutely impossible to be qualified so