Can you compile a .py file with cython instead of a pyx file?

I have a file foo.py, and it contains a very slow function that takes 8 minutes to compute. However, when I change the file to `foo.pyx` and compile it with cython with no other changes, it takes 5 minutes to compute. My question is: if I run `cython foo.py` instead of `cython foo.pyx` and then run `gcc -shared -pthread -fPIC -fwrapv -O2 -Wall -fno-strict-aliasing -I/usr/include/python2.7 -o foo.so foo.c` When I run `import foo`, will python import the `.py` file or the compiled `.so` file? Does the pyx really need to be there, and is there a way to force it to take the `.so` over the `.py` if it exists? The reason for this is that I cannot change the name of foo.py without breaking code on other people's machines, but I'd really like it to be faster for my tests cases. It would be great if I could just compile it locally without worrying about breaking code elsewhere. (I'm testing this as we speak, but its taking awhile)