Cython Pass String To C as Bytes

Question

I need to build a string in python and pass it to the wrapped C lib. The C lib defines the function:

unsigned char load(char const *FileName)

In the .pyx file:

def test():
    PATH = '/usr/lib/libnx.so'
    PATH = <char*>PATH
    load(PATH)

But I get: TypeError: expected bytes, str found

I have tried encoding the python string but get the same error.

Answer 1

In Python, str objects are not byte arrays as in C. To get that, you must encode the string. The default is UTF-8 encoding, which is backwards compatible with ASCII.

Here are two ways to pass the array of bytes:

• Option 1: Define PATH to be a bytes object from the get-go:
  • PATH = b'/usr/lib/libnx.so', or:
  • PATH = 'usr/lib/libnx.so'.encode()
• Option 2: Encode PATH into a byte array when you pass it:
  • load(PATH.encode())