New submission from Timothy Pederick <[email protected]>:
The ctypes ArgumentError exception indicates the location of the problem by
argument number. It counts arguments starting from 1, not 0 as is typical in
Python.
Observed
--------
An example (anonymised) traceback:
Traceback (most recent call last):
...
foreign_function(a, b, c, d)
ctypes.ArgumentError: argument 2: <class 'TypeError'>: wrong type
The error here was with the argument "b".
Expected
--------
Standard, zero-indexed Python counting would suggest that argument 2 should
mean "c", and "b" would be argument 1.
Rationale
---------
This may be as intended, but for me it violates the principle of least surprise.
I *think* this is the vicinity of the bug:
http://hg.python.org/cpython/file/696d3631a4a1/Modules/_ctypes/callproc.c#l1103
_ctypes_extend_error(PyExc_ArgError, "argument %d: ", i+1);
If I'm right and the "i+1" (here and/or in subsequent lines) is the cause, that
definitely makes it look intentional.
----------
components: ctypes
messages: 162251
nosy: perey
priority: normal
severity: normal
status: open
title: ctypes ArgumentError lists arguments from 1, not 0
type: behavior
versions: Python 3.2
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Python tracker <[email protected]>
<http://bugs.python.org/issue14999>
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