[issue20023] _csv.Dialect() does not check type for delimiter, escapechar and quotechar fields

[STINNER Victor]

New submission from STINNER Victor:

Example:

$ ./python -c "import _csv; _csv.Dialect(escapechar=b'x')"
python: Python/ceval.c:4262: call_function: Assertion `(x != ((void *)0) && !PyErr_Occurred()) || (x == ((void *)0) && PyErr_Occurred())' failed.
Abandon (core dumped)

Attached patch should fix this issue and adds a unit test.

Note: I found this issue using Fusil the fuzzer.

----------
files: csv.patch
keywords: patch
messages: 206593
nosy: haypo, serhiy.storchaka
priority: normal
severity: normal
status: open
title: _csv.Dialect() does not check type for delimiter, escapechar and quotechar fields
versions: Python 3.4
Added file: http://bugs.python.org/file33203/csv.patch

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<http://bugs.python.org/issue20023>
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