Using Python.h in C ++ gives the error "no such file or directory"

I am trying to include Python.h in a C ++ file.

#include "Python.h"

int main() {
    return 0;
}

This gives

fatal error: Python.h: No such file or directory

compilation completed.

when compiling.

I installed and added the directory to PATH correctly

echo $PATH
/usr/lib/lightdm/lightdm:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/include:/usr/local/lib:/usr/include/python2.7

What could be the problem?