Python Regex - Reject strings with newline

Question

I want to match complete strings to a specific pattern. Let's say :

word = "aaaa"
test = re.match(r"^aaaa$", word) # this returns True

However, if the word is followed by a newline character :

word = "aaaa\n"
test = re.match(r"^aaaa$", word) # Also returns True :(

But I want to find a way for it to return False in this last case. Is there a way to differentiate "\n"?

Answer 1

Instead of anchors ^ and $ use \A for start and \Z for end:

>>> print re.match(r'\Aaaaa\Z', 'aaaa')
<_sre.SRE_Match object at 0x1014b9bf8>

>>> print re.match(r'\Aaaaa\Z', 'aaaa\n')
None

\A matches the actual start of string and \Z the actual end and there can be only one of \A and \Z in a multiline string, whereas $ may be matched in each line.

I suggest reading this very good article on permanent line anchors.

Just fyi unlike .NET, Java, PCRE, Delphi, PHP in Python \Z matches only at the very end of the string. Python does not support \z.

Answer 2

You can use negative lookaheads for checking if it contains a new line character or not.In your case, ^aaaa(?!\n)$.