CODEWITHSUNDEEP
pythoncython
jeremy
jeremy

Reputation: 4681

In what circumstances does Cython convert structs to dictionaries?

I've read in lots of places (including SO) that cython can convert structs to dictionaries, but I can't seem to find it in the documentation. Does this really happen? If so, under what circumstances does this occur?

I can't get it to do so using the following code:

# pxd:
cdef extern from "main.h":
    ctypedef struct something_t:
        int a
        int b

# pyx:
cdef public void do_stuff(something_t *number):
    number.a = 1  # works
    number[0].a = 2  # works

    number['a'] = 3  # doesn't work: Cannot assign type 'long' to 'something_t'
    number[0]['a'] = 4  # doesn't work: Cannot assign type 'long' to 'something_t'

Upvotes: 1

Views: 911

Answers (1)

Nikita Nemkin
Nikita Nemkin

Reputation: 2820

It happens when a variable of C struct type (cdef struct or ctypedef struct) is converted to a variable of Python object type.

cdef something_t s = [1, 2]  # declare and initialize C struct
cdef object sobj = s  # sobj is assigned {'a': 1, 'b': 2} from s data

It's just an automatic conversion, nothing more. You can't use dict syntax with C structs or C struct syntax with Python dicts like in your example.

Upvotes: 2

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