CODEWITHSUNDEEP
pythonregexexpression
Yar
Yar

Reputation: 7457

difference between these two regular expression

could somebody explain the difference between these two Regular Expression:

re.search('^[abcd]z$', noun)

and

re.search('[^abcd]z$', noun)

Thanks!

Upvotes: 1

Views: 66

Answers (1)

unutbu
unutbu

Reputation: 879381

'^[abcd]z$' must match starting at the beginning of the string.

'[^abcd]z$ matches anything with is not in the character class [abcd], followed by a z.

As you can see, the ^ has vastly different meanings inside and outside of the brackets. Outside the brackets, ^ matches the start of the string, while if ^ is the first character inside brackets, it indicates a complementing set.

This matches, since 'dz' starts with a character in [abcd].

In [102]: re.search('^[abcd]z', 'dz')
Out[102]: <_sre.SRE_Match at 0xa12b480>

This does not match since [^abcd] matches anything but a, b, c or d. 

In [103]: re.search('[^abcd]z', 'dz')

While this does match since e is not in [abcd].

In [104]: re.search('[^abcd]z', 'ez')
Out[104]: <_sre.SRE_Match at 0xa12b3a0>

Per the docs:

'^': (Caret.) Matches the start of the string, and in MULTILINE mode also matches immediately after each newline.

'[]': Characters that are not within a range can be matched by complementing the set. If the first character of the set is '^', all the characters that are not in the set will be matched. For example, [^5] will match any character except '5', and [^^] will match any character except '^'. ^ has no special meaning if it’s not the first character in the set.

Upvotes: 3

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