[New-bugs-announce] [issue12265] revamp argument errors

[Benjamin Peterson]

New submission from Benjamin Peterson <benjamin at python.org>:

This patch completely rewrites errors given for positional error mismatches. The goal is to give more informative and correct errors.

Some examples:

>>> def f(): pass
... 
>>> f(1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: f() takes 0 positional arguments but 1 was given
>>> f(1, kw=4)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: f() got an unexpected keyword argument 'kw'
>>> def f(a, b=2): pass
... 
>>> f()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: f() takes from 1 to 2 positional arguments but 0 were given
>>> f(1, 2, 3)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: f() takes from 1 to 2 positional arguments but 3 were given
>>> def f(a, *b): pass
... 
>>> f()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: f() takes at least 1 positional argument but 0 were given
>>> f(kw=4)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: f() got an unexpected keyword argument 'kw'

When keyword-only arguments come into play, things get a bit more complicated. When a positional argument error occurs, it's confusing to report only the positional arguments, but not completely relevant to report keyword-only arguments. I comprise by putting the keyword-only argument information in parenthesis. Tell me if you have a better idea.

>>> def f(*, kw): pass
... 
>>> f()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: f() requires keyword-only argument 'kw'
>>> f(1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: f() takes 0 positional arguments but 1 was given
>>> f(3, kw=4)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: f() takes 0 positional arguments but 1 positional arguments (and 1 keyword-only argument) were given

----------
components: Interpreter Core
files: argerror.patch
keywords: patch
messages: 137676
nosy: benjamin.peterson
priority: normal
severity: normal
stage: patch review
status: open
title: revamp argument errors
type: feature request
versions: Python 3.3
Added file: http://bugs.python.org/file22252/argerror.patch

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue12265>
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