[Python-Dev] Python Library Addition: First-class Procedure Signatures (original) (raw)

Brett Cannon brett at python.org
Wed Nov 14 21🔞56 CET 2007

On Nov 14, 2007 10:30 AM, Isaac Morland <ijmorlan at cs.uwaterloo.ca> wrote:

For another project (see my previous email on named tuples), I needed to represent procedure signatures, and use them to expand arguments into the dictionary of values that exists when execution of a procedure starts. To my surprise, this capability didn't seem to be provided by the Python library, even though it clearly is present within the Python system somewhere.

So I wrote a Signature class. Instances of the class represent all the information present between the parentheses of a procedure definition. Properties are provided to get the information out, and an expandargs method can be called to expand arguments into a dictionary. This expandargs method implements (if I've done it right) the argument conversion part of section 5.3.4 of the Python Reference Manual (http://docs.python.org/ref/calls.html).

As Collin already pointed out, it sounds like you want PEP 362 to get into the stdlib. I have not made a big push to try to get my existing implementation into Python 2.6/3.0, but I plan to at some point.

I've put the code below, but I wonder if the real solution is just to create an interface to already-existing capability? It occurs to me that the implementation is likely to be in the interpreter itself and not written in Python.

I don't see why a Python implementation is bad. If you make this information lazy then it is not such a big deal to have it take a little bit longer than if it was implemented in C.

One possible improvement (and I'm not sure it's better, so I'm just putting it out there): perhaps expandargs should be renamed to call. Then essentially a Signature object would be a procedure whose body is just "return locals ()".

call is already used a method name for objects that can be called.

-Brett

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