Efficient way to search for invalid characters in python

Question

I am building a forum application in Django and I want to make sure that users dont enter certain characters in their forum posts. I need an efficient way to scan their whol

Answer 1

You have to be much more careful when using regular expressions - they are full of traps.

in the case of [^<>/\{}[]~] the first ] closes the group which is probably not what you intended. If you want to use ] in a group it has to be the first character after the [ eg []^<>/\{}[~]

simple test confirms this

>>> import re
>>> re.search("[[]]","]")
>>> re.search("[][]","]")
<_sre.SRE_Match object at 0xb7883db0>

regex is overkill for this problem anyway

def clean_topic_message(self):
    topic_message = self.cleaned_data['topic_message']
    invalid_chars = '^<>/\{}[]~`$'
    if (topic_message == ""):
        raise forms.ValidationError(_(u'Please provide a message for your topic'))
    if set(invalid_chars).intersection(topic_message):
        raise forms.ValidationError(_(u'Topic message cannot contain the following: %s'%invalid_chars))
    return topic_message