[issue9723] Add shlex.quote

[Ezio Melotti]

Ezio Melotti <ezio.melotti at gmail.com> added the comment:

+_find_unsafe = re.compile(r'[^\w\d@%_\-\+=:,\./]').search

\w already includes both \d and _, so (unless you really want to be explicit about it) they are redundant.  Also keep in mind that they match non-ASCII letters/numbers on Python 3.
'+' and '.' don't need to be escaped in a character class (i.e. [...]), because they lose their meta-characters meaning there.
'-' is correctly escaped there, but it's common practice to place it at the end of the character class, where it doesn't need escaping.

r'[^\w\d@%_\-\+=:,\./]' and r'[^\w@%+=:,./-]' should therefore be equivalent.

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<http://bugs.python.org/issue9723>
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