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read() and readline() optional parameter which limit the amount of read data has different names in different classes. All this classes mimic (less or more) io classes. Keyword parameter name is a part of method specification. Therefore it will be good made all read() arguments names the same and all readline() arguments names the same (and be consistent with documentation and C implementation). At least we should choose most consistent name for new implementations. If existent C implementation of some method doesn't support keyword argument (all _io classes) or argument names in C and Python implementations are different then we are free to change this name without breaking existing code.
For example, read()'s parameter named as:
"n" in _pyio, zipfile, and io documentation;
"size" in gzip, bz2, imaplib, tarfile, codecs, mailbox;
"len" in ssl;
"wtd" or "totalwtd" in binhex;
"amt" in http/client;
"chars" in codecs;
"buffersize" in os.
readline()'s parameter named as:
"limit" in _pyio, zipfile, and io documentation;
"size" in gzip, bz2, codecs, mailbox, lzma.

Looks as size is most common parameter name for both read() and readline(). First, we can change the io documentation and _pyio signatures (it shouldn't break anything because _io doesn't support keyword arguments).

"n" is the best choice IMO. "size" is ok too, although it may be confused with the byte-size of the result.

Here is a patch which changes name of optional parameter of read(), read1(), peek(), and readline() methods to most common name "size" in the documentation and _pyio module. truncate() in _pyio fixed to conform with documentation. This changes are safe.
There is open question about readlines(). It's optional parameter named as:
"hint" in _pyio and the documentation;
"size" in bz2;
"sizehint" in codecs and mailbox.

> "n" is the best choice IMO.
Unfortunately most stdlib modules vote for "size".

Are there any objections to the patch?

New changeset 46c1c2b34e2b by Serhiy Storchaka in branch 'default':
Issue #17003: Unified the size argument names in the io module with common
http://hg.python.org/cpython/rev/46c1c2b34e2b 

Is there anything left for this bug or could it be closed? I can confirm my v3.4.2 docs say "size" instead of "n" :)

readlines() parameter name is not unified still (it can be "hint", "size", "sizehint"). There is no obvious winner.