Regex: don't match string ending with newline (\n) with end-of-line anchor ($)

Question

I can\'t figure out how to match a string but not if it has a trailing newline character (\\n), which seems automatically stripped:

import re

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Answer 1

The documentation says this about the $ character:

Matches the end of the string or just before the newline at the end of the string, and in MULTILINE mode also matches before a newline.

So, without the MULTILINE option, it matches exactly the first two strings you tried: 'foobar' and 'foobar\n', but not 'foobar\n\n', because that is not a newline at the end of the string.

On the other hand, if you choose MULTILINE option, it will match the end of any line:

>>> re.match(r'^foobar$', 'foobar\n\n', re.MULTILINE)
<_sre.SRE_Match object; span=(0, 6), match='foobar'>

Of course, this will also match in the following case, which may or may not be what you want:

>>> re.match(r'^foobar$', 'foobar\nanother line\n', re.MULTILINE)
<_sre.SRE_Match object; span=(0, 6), match='foobar'>

In order to NOT match the ending newline, use the negative lookahead as DeepSpace wrote.