CODEWITHSUNDEEP
regexpython-3.x
Aleksandr Zonov
Aleksandr Zonov

Reputation: 185

Using * in a sets in a python regex

In python 3.2.2 I confronted with strange errors when I try to use * in regex patterns. When * stads after / all is ok. But when I try to remove / from patter, this code falls down with error: sre_constants.error: bad character range

import re
foo = re.search("[^123+-/*]", "123+-/*w")
if foo:
    print("foo")
else:
    print("doo")

In the python docs I found that using * is acceptable without any backslashes or other stuff. However problem with code like this remains.

Upvotes: 4

Views: 2081

Answers (2)

mjhennig
mjhennig

Reputation: 681

The minus is causing the last characters to get interpreted as a character range. [+-/] acutally means "any of +,-./" (see the ASCII table). When you replace the / by *, you're creating the invalid range [+-*] because the ASCII code of the asterisk, 42, is less than the ASCII codes of the plus, 43.

The solution is simply escaping the minus (then it's not a range any more).

Upvotes: 2

Joey
Joey

Reputation: 354694

Your problem isn't *, it's the hyphen-minus which represents a range in a character class, in this case all characters between + and / (+,-./). The invalid range occurs because * comes before /.

If you want to include a literal hyphen in a character class you have to either escape it or put it at the very end or start:

[^123+/*-]

Upvotes: 5

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