[regex] Which regular expression operator means 'Don't' match this character?

*, ?, + characters all mean match this character. Which character means 'don't' match this? Examples would help.

There's two ways to say "don't match": character ranges, and zero-width negative lookahead/lookbehind.

The former: don't match a, b, c or 0: [^a-c0]

The latter: match any three-letter string except foo and bar:

(?!foo|bar).{3}

or

.{3}(?<!foo|bar)

Also, a correction for you: *, ? and + do not actually match anything. They are repetition operators, and always follow a matching operator. Thus, a+ means match one or more of a, [a-c0]+ means match one or more of a, b, c or 0, while [^a-c0]+ would match one or more of anything that wasn't a, b, c or 0.

[^] ( within [ ] ) is negation in regular expression whereas ^ is "begining of string"

[^a-z] matches any single character that is not from "a" to "z"

^[a-z] means string starts with from "a" to "z"

Reference

^ used at the beginning of a character range, or negative lookahead/lookbehind assertions.

>>> re.match('[^f]', 'foo')
>>> re.match('[^f]', 'bar')
<_sre.SRE_Match object at 0x7f8b102ad6b0>
>>> re.match('(?!foo)...', 'foo')
>>> re.match('(?!foo)...', 'bar')
<_sre.SRE_Match object at 0x7f8b0fe70780>