New submission from STINNER Victor:
When a function has only positional arguments and at least one argument is
optional, the expected signature is:
func(mandatory_arg1, mandatory_arg2[, optional_arg3[, optinal_arg4]])
For example, the signature of format() is inconsistent with its documentation.
Signature:
---
$ python3 -c 'help(format)'|cat
Help on built-in function format in module builtins:
format(value, format_spec='', /)
Return value.__format__(format_spec)
format_spec defaults to the empty string
---
Documentation:
---
.. function:: format(value[, format_spec])
---
Attached patch is a first attempt to fix the issue. The problem is that my
heuristic to check if an argument is "optional" doesn't seem to work as
expected in all cases. I chose to check if the C default is NULL.
The problem is that some functions defines a C default to NULL whereas the
Python default is set to a different value and is correct.
Example with _io.FileIO.truncate:
/*[clinic input]
_io.FileIO.truncate
size as posobj: object = NULL
/
whereas the documentation says that the default is None:
.. method:: truncate(size=None)
It's easy to fix the default, but in this case my change doesn't fix the
signature anymore since the C default is still NULL:
/*[clinic input]
_io.FileIO.truncate
size as posobj: object(c_default="NULL") = None
/
We need a different heuristic than C default is NULL, or we should fix
functions where the heuristic fails.
----------
components: Argument Clinic
files: ac_optional_positional.patch
keywords: patch
messages: 285650
nosy: haypo, larry, rhettinger, serhiy.storchaka
priority: normal
severity: normal
status: open
title: Argument Clinic: Fix signature of optional positional-only arguments
versions: Python 3.7
Added file: http://bugs.python.org/file46316/ac_optional_positional.patch
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<http://bugs.python.org/issue29299>
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