Re: [Cython] Creating python bindings for C library using Cython

Chris Colbert wrote:
> python strings are automagically converted to char* by cython.
I'll beat Stefan to it and note some very important points here. This 
applies if you actually have a string (e.g. could be stored in "unicode" 
in Py2), not if you have raw byte data ("bytes" in Py3).

1) A C char* is not a string as such, just a sequence of bytes. The C 
library should have a definition of what kind of encoding it wants its 
strings in, and one should call the library like this:

encoded = mystr.encode(encoding)
cdef char* encoded_buf = encoded
c_func(encoded_buf)

2) Note that char* does not say anything about releasing memory etc. 
I.e., the following will likely crash:

c_func(mystr.encode(encoding))

because the temporary object returned from the encode method is 
deallocated. *Always* keep a reference to the original Python object for 
the duration someone could use the char*.

(Perhaps somebody could make this a FAQ entry in the wiki if it is not 
already?)

Dag Sverre