C Extension question-> How handle lists and tuples as arguments?

[Christian Seberino]

Py_ParseTuple is a great C function to set C variables from
Python objects in a C extension.

Usage is straight forward for integers and strings but I'm wondering
what to do if I ever want to send in a list or tuple.

First problem is that we don't know the LENGTH of the list/tuple.

Second problem is we don't know the TYPES of the elements.

Chris

[Gerhard Häring]

Christian Seberino wrote:

Py_ParseTuple is a great C function to set C variables from
Python objects in a C extension.

Usage is straight forward for integers and strings but I'm wondering
what to do if I ever want to send in a list or tuple.

First problem is that we don't know the LENGTH of the list/tuple.

Second problem is we don't know the TYPES of the elements.

I don't understand your problem. For "other" parameters, use "O" as
format character in ParseTuple...(). Then if you need to check if the
passed parameter is a sequence (either tuple or list), you can just use
PySequenceCheck().

For the rest, use the functions for the sequence protocol, like
PySequence_Length() and the like.

HTH,

-- Gerhard

[Martin v. Löwis]

se******@spawar.navy.mil (Christian Seberino) writes:

Py_ParseTuple is a great C function to set C variables from
Python objects in a C extension.
I disagree. It is much better to use specific functions.
Usage is straight forward for integers and strings but I'm wondering
what to do if I ever want to send in a list or tuple.

First problem is that we don't know the LENGTH of the list/tuple.

Second problem is we don't know the TYPES of the elements.

Just like you would do it in Python:

len(x) --> PyObject_Length(x)
x[i] --> PySequence_GetItem(x, i) (assuming x is a sequence)
isinstance(o, int) --> PyInt_Check(o)
obtain native value --> PyInt_AsLong(o)

HTH,
Martin