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Diffstat (limited to 'Doc/howto/regex.rst')
| -rw-r--r-- | Doc/howto/regex.rst | 27 |
1 files changed, 21 insertions, 6 deletions
diff --git a/Doc/howto/regex.rst b/Doc/howto/regex.rst index eef6347..a3a6553 100644 --- a/Doc/howto/regex.rst +++ b/Doc/howto/regex.rst @@ -289,6 +289,8 @@ Putting REs in strings keeps the Python language simpler, but has one disadvantage which is the topic of the next section. +.. _the-backslash-plague: + The Backslash Plague -------------------- @@ -327,6 +329,13 @@ backslashes are not handled in any special way in a string literal prefixed with while ``"\n"`` is a one-character string containing a newline. Regular expressions will often be written in Python code using this raw string notation. +In addition, special escape sequences that are valid in regular expressions, +but not valid as Python string literals, now result in a +:exc:`DeprecationWarning` and will eventually become a :exc:`SyntaxError`, +which means the sequences will be invalid if raw string notation or escaping +the backslashes isn't used. + + +-------------------+------------------+ | Regular String | Raw string | +===================+==================+ @@ -457,12 +466,18 @@ In actual programs, the most common style is to store the Two pattern methods return all of the matches for a pattern. :meth:`~re.pattern.findall` returns a list of matching strings:: - >>> p = re.compile('\d+') + >>> p = re.compile(r'\d+') >>> p.findall('12 drummers drumming, 11 pipers piping, 10 lords a-leaping') ['12', '11', '10'] -:meth:`~re.pattern.findall` has to create the entire list before it can be returned as the -result. The :meth:`~re.pattern.finditer` method returns a sequence of +The ``r`` prefix, making the literal a raw string literal, is needed in this +example because escape sequences in a normal "cooked" string literal that are +not recognized by Python, as opposed to regular expressions, now result in a +:exc:`DeprecationWarning` and will eventually become a :exc:`SyntaxError`. See +:ref:`the-backslash-plague`. + +:meth:`~re.Pattern.findall` has to create the entire list before it can be returned as the +result. The :meth:`~re.Pattern.finditer` method returns a sequence of :ref:`match object <match-objects>` instances as an :term:`iterator`:: >>> iterator = p.finditer('12 drummers drumming, 11 ... 10 ...') @@ -1096,11 +1111,11 @@ following calls:: The module-level function :func:`re.split` adds the RE to be used as the first argument, but is otherwise the same. :: - >>> re.split('[\W]+', 'Words, words, words.') + >>> re.split(r'[\W]+', 'Words, words, words.') ['Words', 'words', 'words', ''] - >>> re.split('([\W]+)', 'Words, words, words.') + >>> re.split(r'([\W]+)', 'Words, words, words.') ['Words', ', ', 'words', ', ', 'words', '.', ''] - >>> re.split('[\W]+', 'Words, words, words.', 1) + >>> re.split(r'[\W]+', 'Words, words, words.', 1) ['Words', 'words, words.'] |