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Diffstat (limited to 'Doc/library/re.rst')
| -rw-r--r-- | Doc/library/re.rst | 22 |
1 files changed, 14 insertions, 8 deletions
diff --git a/Doc/library/re.rst b/Doc/library/re.rst index b196a28..ac07cf8 100644 --- a/Doc/library/re.rst +++ b/Doc/library/re.rst @@ -330,16 +330,22 @@ the second character. For example, ``\$`` matches the character ``'$'``. Matches the empty string, but only at the beginning or end of a word. A word is defined as a sequence of Unicode alphanumeric or underscore characters, so the end of a word is indicated by whitespace or a - non-alphanumeric, non-underscore Unicode character. Note that - formally, ``\b`` is defined as the boundary between a ``\w`` and a - ``\W`` character (or vice versa). By default Unicode alphanumerics - are the ones used, but this can be changed by using the :const:`ASCII` - flag. Inside a character range, ``\b`` represents the backspace - character, for compatibility with Python's string literals. + non-alphanumeric, non-underscore Unicode character. Note that formally, + ``\b`` is defined as the boundary between a ``\w`` and a ``\W`` character + (or vice versa), or between ``\w`` and the beginning/end of the string. + This means that ``r'\bfoo\b'`` matches ``'foo'``, ``'foo.'``, ``'(foo)'``, + ``'bar foo baz'`` but not ``'foobar'`` or ``'foo3'``. + + By default Unicode alphanumerics are the ones used, but this can be changed + by using the :const:`ASCII` flag. Inside a character range, ``\b`` + represents the backspace character, for compatibility with Python's string + literals. ``\B`` - Matches the empty string, but only when it is *not* at the beginning or end of a - word. This is just the opposite of ``\b``, so word characters are + Matches the empty string, but only when it is *not* at the beginning or end + of a word. This means that ``r'py\B'`` matches ``'python'``, ``'py3'``, + ``'py2'``, but not ``'py'``, ``'py.'``, or ``'py!'``. + ``\B`` is just the opposite of ``\b``, so word characters are Unicode alphanumerics or the underscore, although this can be changed by using the :const:`ASCII` flag. |