[Python-Dev] AC Derby and accepting None for optional positional arguments (original) (raw)

Tres Seaver tseaver at palladion.com
Thu Jan 16 23:12:32 CET 2014

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On 01/16/2014 04:08 PM, Ryan Smith-Roberts wrote:

[L]et us return to my original example, getservbyname(). Its current signature:

socket.getservbyname(servicename[, protocolname]) This is not an inspectable signature, since pure Python does not support bracketed arguments. To make it inspectable, we must give protocolname a (valid Python) default value: socket.getservbyname(servicename, protocolname=None) Unfortunately, while useful and inspectable, this signature is not correct. For a pure Python function, passing None for protocolname is the same as omitting it. However, if you pass None to getservbyname(), it raises a TypeError. So, we have these three options: 1) Don't give getservbyname() an inspectable signature. 2) Lie to the user about the acceptability of None. 3) Alter the semantics of getservbyname() to treat None as equivalent to omitting protocolname. Obviously #2 is out. My question: is #3 ever acceptable? It's a real change, as it breaks any code that relies on the TypeError exception.

+1 for #3, especially in a new "major" release (w/ sufficient documentation of the change).

Tres. - --

Tres Seaver +1 540-429-0999 tseaver at palladion.com Palladion Software "Excellence by Design" http://palladion.com -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/

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