Bindings type checking too strict

[rogerbinns]

Bindings for cursor.execute/executemany can conceptually either be a dictionary (lookup by key) or a sequence (lookup by position).

Currently PyDict_Check is used to determine if it is a dictionary, otherwise PySequence_Fast is used for positional access.

Because PyDict_Check only looks for dict subclasses, it means that UserDict won't work. The apparent solution of PyMapping_Check returns True for UserDict, but also for lists and tuples.

For reference, this is what the builtin _sqlite3 module does

Treat as not a dictionary if:

PyTuple_CheckExact(parameters) || PyList_CheckExact(parameters) 
|| (!PyDict_Check(parameters) && PySequence_Check(parameters))

Otherwise treat as dictionary if:

PyDict_Check(parameters)

Otherwise error

[rogerbinns]

Some tests with various types that shows we can't tell dict/list apart:

dict_check 0 sequence_check 1 mapping_check 1: collections.UserDict
dict_check 0 sequence_check 1 mapping_check 1: list()
dict_check 1 sequence_check 0 mapping_check 1: dict()
dict_check 0 sequence_check 1 mapping_check 1: class with only __getitem__

collections.abc.Mapping does seem to be useful. isinstance(T, collections.abc.Mapping)

True: dict
True: collections.UserDict
False: list
False: set
False: class with only __getitem__

It looks like this is the most useful, especially as custom classes can register with collections.abc.Mapping