Error “ a bytes-like object is required, not 'str'” when using f2py in Python 3 environment

Question

I found out that my f2py in python 3 environment may not be installed correctly. Therefore, I tried to test the f2py using the file follows:

$vi forMatMul_ref.f90  
     subroutine matrixMult (C , A , B , n )
     implicit none
     integer , intent (in) :: n
     real *8 , intent (in) :: A (n , n )
     real *8 , intent (in) :: B (n , n )
     real *8 , intent ( out ) :: C (n , n )
     C = matmul (A , B )         
     return
     end subroutine matrixMultul_ref.f90

Then I test the file in IPYTHON:

import numpy as np
import numpy . f2py as f2py

fid = open ("forMatMul_ref.f90")    
source = fid.read()
fid.close()

f2py.compile(source, modulename = "forMatMul")
import forMatMul
AB =  forMatMul . matrixmult (A , B )

However, the error appears when running the compilation processes of f2py shows like:

TypeError Traceback (most recent call last) in () ----> 1 f2py.compile(source, modulename='forMatMul')

/Users/HYF/anaconda/envs/py35/lib/python3.5/site-packages/numpy/f2py/__init__.py in compile(source, modulename, extra_args, verbose, source_fn, extension)
     57 
     58     try:
---> 59         f.write(source)
     60         f.flush()
     61 

/Users/HYF/anaconda/envs/py35/lib/python3.5/tempfile.py in func_wrapper(*args, **kwargs)
    481             @_functools.wraps(func)
    482             def func_wrapper(*args, **kwargs):
--> 483                 return func(*args, **kwargs)
    484             # Avoid closing the file as long as the wrapper is alive,
    485             # see issue #18879.

TypeError: a bytes-like object is required, not 'str'

Some essential information are provided here:

## Computer OS
Darwin I.local 14.3.0 Darwin Kernel Version 14.3.0: Mon Mar 23 11:59:05 PDT 2015; root:xnu-2782.20.48~5/RELEASE_X86_64 x86_64 i386 MacBookAir7,2 Darwin
## Python environment
/Users/HYF/anaconda/envs/py35/bin/python
## Fortran compiler (GCC 4.9.4 contains both C and Fortran compiler)
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/x86_64-apple-darwin14.0.0/4.9.2/lto-wrapper
Target: x86_64-apple-darwin14.0.0
Configured with: ../gcc-4.9-20141029/configure --enable-languages=c++,fortran
Thread model: posix
gcc version 4.9.2 20141029 (prerelease) (GCC) 
(py35) 

I would like to have an advice how to proceed.

PS

I have fixed this problem by editing the _init_py in numpy/numpy/f2py/.

Answer 1

Try opening the file in binary mode - open("forMatMul_ref.f90", "rb") - it will give you raw bytes for the source code (which seems to be what it expects) rather than decoding to a string. This is probably a side-effect of them porting legacy python 2 code to run in python 3, otherwise a string object would seemingly be an appropriate representation for source code. If you are interested, this post describes what changed with strings between Python 2 and 3: https://timothybramlett.com/Strings_Bytes_and_Unicode_in_Python_2_and_3.html