urllib.quote('()')
returns '%28%29'

Looking into its code it tries to follow RFC 2396 (which is good even though it should follow rfc3986 nowadays), but it doesn't:

http://tools.ietf.org/html/rfc2396 (see Appendix A, p.27): "(" and ")" are in mark and therefore unreserved, so why are they quoted?

It can aggressively put these chars !~*\'() in the safe list.  I will look at the history to see if they originally present and were removed for some reason or they did not make it the list in the first place. 

If we do add, then it should be only 3.3 (Someone could be relying on the old behavior).

Issue 16285 updated the urllib.parse.quote() reserved list to add '~'.

From the docstring:
def quote(string, safe='/', encoding=None, errors=None):
    """quote('abc def') -> 'abc%20def'

    Each part of a URL, e.g. the path info, the query, etc., has a
    different set of reserved characters that must be quoted.

    RFC 3986 Uniform Resource Identifiers (URI): Generic Syntax lists
    the following reserved characters.

    reserved    = ";" | "/" | "?" | ":" | "@" | "&" | "=" | "+" |
                  "$" | "," | "~"

    Each of these characters is reserved in some component of a URL,
    but not necessarily in all of them.

    Python 3.7 updates from using RFC 2396 to RFC 3986 to quote URL strings.
    Now, "~" is included in the set of reserved characters.

--------------------------------------------
However, looking at RFC3986 (https://tools.ietf.org/html/rfc3986), appendix A has the following:

   unreserved    = ALPHA / DIGIT / "-" / "." / "_" / "~"
   reserved      = gen-delims / sub-delims
   gen-delims    = ":" / "/" / "?" / "#" / "[" / "]" / "@"
   sub-delims    = "!" / "$" / "&" / "'" / "(" / ")"
                 / "*" / "+" / "," / ";" / "="

----------------------------------------------------
Should the missing ones be added or should this issue be closed if they aren't going to be added?

Thanks.

It's been a while... nowadays I would mostly change the documentation of the quote function to point out that it is likely to quote more characters than absolutely necessary by SPEC. The function is in place for so long, (even in py3) that people will rely on the behavior.

I made an attempt to update the docstring accordingly in https://github.com/python/cpython/pull/2568


What i think is most confusing is the current docs mentioning the reserved chars (which are btw. definitely wrong wrt. RFC3986). Actually as one can see in the code the reserved chars don't play any role for quote, but much more the unreserved chars (called _ALWAYS_SAFE https://github.com/python/cpython/blob/master/Lib/urllib/parse.py#L716 ).

   unreserved    = ALPHA / DIGIT / "-" / "." / "_" / "~"

The current quote function's approach is to simply quote everything that is not in unreserved + safe (per arg).

In that aspect it is quite close to the old javascript.escape function: https://www.w3schools.com/jsref/jsref_escape.asp


quick links
py2.7: https://github.com/python/cpython/blob/2.7/Lib/urllib.py#L1261
py3: https://github.com/python/cpython/blob/master/Lib/urllib/parse.py#L745
RFC3986: https://tools.ietf.org/html/rfc3986#appendix-A

New changeset 750d74fac5c510e39958b3f79641fe54096ee54f by Senthil Kumaran (Jörn Hees) in branch 'master':
bpo-12910: update and correct quote docstring (#2568)
https://github.com/python/cpython/commit/750d74fac5c510e39958b3f79641fe54096ee54f

New changeset 796698adf558f2255474945082856538b1effb0b by Miss Islington (bot) in branch '3.7':
bpo-12910: update and correct quote docstring (GH-2568)
https://github.com/python/cpython/commit/796698adf558f2255474945082856538b1effb0b