How to pass a numpy array of string types to a function in Cython

Question

Passing a numpy array of dtype np.float64_t works fine ( below), but I can't pass string arrays.

This is what works :

# cython_testing.pyx
import numpy as np
cimport numpy as np

ctypedef np.float64_t dtype_t 

cdef func1 (np.ndarray[dtype_t, ndim=2] A):
    print A 

def testing():
    chunk = np.array ( [[94.,3.],[44.,4.]], dtype=np.float64)

    func1 (chunk)

But I can't make this work: I can't find the matching 'type identifiers' for numpy string dtypes.

# cython_testing.pyx
import numpy as np
cimport numpy as np

ctypedef np.string_t dtype_str_t 

cdef func1 (np.ndarray[dtype_str_t, ndim=2] A):
    print A 

def testing():
    chunk = np.array ( [['huh','yea'],['swell','ray']], dtype=np.string_)

    func1 (chunk)

The compilation error is :

Error compiling Cython file:
------------------------------------------------------------
ctypedef np.string_t dtype_str_t 
    ^
------------------------------------------------------------

cython_testing.pyx:9:9: 'string_t' is not a type identifier

UPDATE

Per looking through numpy.pxd, I see the following ctypedef statements. Maybe that's enough to say I can use uint8_t and pretend everything is normal, as long as I can do some casting?

ctypedef unsigned char      npy_uint8
ctypedef npy_uint8      uint8_t

Just have to see how expensive that casting will be.

Answer 1

With Cython 0.20.1 it works using cdef np.ndarray, without specifying the data type and the number of dimensions:

import numpy as np
cimport numpy as np

cdef func1(np.ndarray A):
    print A

def testing():
    chunk = np.array([['huh','yea'], ['swell','ray']])
    func1(chunk)

Answer 2

Looks like you're out of luck.

http://cython.readthedocs.org/en/latest/src/tutorial/numpy.html

Some data types are not yet supported, like boolean arrays and string arrays.

---

This answer is no longer valid as shown by Saullo Castro's answer, but I'll leave it for historical purposes.