Python regex bad character range.

Question

I am using the following regex to match different patterns of dates. it works fine in regex101.com. But when I import to python i am getting "bad character range" exception.

  pattern = ur"((?:\b((?:(january|jan|february|feb|march|mar|april|apr|may|jun|june|july|jul|august|aug|september|set|sep|october|oct|november|nov|december|dec)['\s\.]{0,4}(?:\d{4}|\d{2})|(?:january|jan|february|feb|march|mar|april|apr|may|jun|june|july|jul|august|aug|september|set|sep|october|oct|november|nov|december|dec)|((?:0[1-9]|[1-3][0-9]|[0-9])/(?:0[1-9]|[1-3][0-9])/(?:(19[7-9][0-9])|(20[0-1][0-9])|([7-9][0-9]|[0-1][0-9]))|((?:0[1-9]|1[0-2]|[1-9])\s{0,3}[-/']{1,3}[\s-/']{0,3}(?:(19[7-9][0-9])|(20[0-1][0-9])|([7-9][0-9]|[0-1][0-9])))))(?:(?![\r\n])\s){0,4})[-/–to]{0,2}(?:(?![\r\n])\s){0,4}(((?:january|jan|february|feb|march|mar|april|apr|may|jun|june|july|jul|august|aug|september|set|sep|october|oct|november|nov|december|dec)[-'\s\.]{0,4}(?:(19[7-9][0-9])|(20[0-1][0-9])|([7-9][0-9]|[0-1][0-9])))|((?:0[1-9]|[1-3][0-9]|[1-9])/(?:0[1-9]|[1-3][0-9])/(?:(19[7-9][0-9])|(20[0-1][0-9])|([7-9][0-9]|[0-1][0-9])))|((?:0[1-9]|1[0-2]|[1-9])\s{0,3}[-/']{1,3}[\s-/']{0,3}(?:(19[7-9][0-9])|(20[0-1][0-9])|([7-9][0-9]|[0-1][0-9]))))))"

  https://regex101.com/r/rU3cE9/1

@AvinashRaj - I include a lot of hyphens. I have a doubt that, it won't be because of regular hyphen ( - ) right ? But, how come regex101.com doesn't show a error. — user3116355
– user3116355, Commented Feb 16, 2015 at 10:27
There are many libraries that does that for you.. no need for regex here. — Maroun
– Maroun, Commented Feb 16, 2015 at 10:28

handras · Accepted Answer · 2019-01-10 14:55:57Z

58

Problem is mainly because of the hyphen present inside [\s-/'] character class, therefore Python interprets it as a character interval (like in [a-z]). I suggest you to put the hyphen at the first or at the last position inside the character class [-\s/'] or escape it, to prevent ambiguity.

>>> reg = re.compile(ur"((?:\b((?:(january|jan|february|feb|march|mar|april|apr|may|jun|june|july|jul|august|aug|september|set|sep|october|oct|november|nov|december|dec)['\s\.]{0,4}(?:\d{4}|\d{2})|(?:january|jan|february|feb|march|mar|april|apr|may|jun|june|july|jul|august|aug|september|set|sep|october|oct|november|nov|december|dec)|((?:0[1-9]|[1-3][0-9]|[0-9])/(?:0[1-9]|[1-3][0-9])/(?:(19[7-9][0-9])|(20[0-1][0-9])|([7-9][0-9]|[0-1][0-9]))|((?:0[1-9]|1[0-2]|[1-9])\s{0,3}[-/']{1,3}[-\s/']{0,3}(?:(19[7-9][0-9])|(20[0-1][0-9])|([7-9][0-9]|[0-1][0-9])))))(?:(?![\r\n])\s){0,4})[-/to–]{0,2}(?:(?![\r\n])\s){0,4}(((?:january|jan|february|feb|march|mar|april|apr|may|jun|june|july|jul|august|aug|september|set|sep|october|oct|november|nov|december|dec)[-'\s\.]{0,4}(?:(19[7-9][0-9])|(20[0-1][0-9])|([7-9][0-9]|[0-1][0-9])))|((?:0[1-9]|[1-3][0-9]|[1-9])/(?:0[1-9]|[1-3][0-9])/(?:(19[7-9][0-9])|(20[0-1][0-9])|([7-9][0-9]|[0-1][0-9])))|((?:0[1-9]|1[0-2]|[1-9])\s{0,3}[-/']{1,3}[-\s/']{0,3}(?:(19[7-9][0-9])|(20[0-1][0-9])|([7-9][0-9]|[0-1][0-9]))))))")
>>>

edited Jan 10, 2019 at 14:55

handras

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answered Feb 16, 2015 at 10:35

Avinash Raj

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5 Comments

user3116355 Over a year ago

I got this. But one doubt. Some other expressions here had same type of hyphen, and that was even not at the end. But only this one seem to be caused an error.

Avinash Raj Over a year ago

i think it's because , of \s (matches any vertical or horizontal space character). So re module failed to find a range between multiple chars and a forward slash. re module is designed like that.

user3116355 Over a year ago

Thanks man. Thanks that you find time to share knowledge and info.

Travis Over a year ago

So what is the hyphen doing here. i.e. Why does it need to be at the beginning or end of the string?

ShreevatsaR Over a year ago

@Travis A hyphen is used in regexes (specifically inside [] in regexes) to denotes a character range, e.g. [a-z] denotes any lowercase alphabetic character. In this case, [\s-/'] is not a character range, so Python complains that it is a "bad character range". Putting the hyphen at the beginning or end (or escaping it) makes Python not interpret it as a character range.

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