It runs at 1/10 speed because it's interpreted bytecode, and it allocates a new PyInt object for each number in the loop. You can get it back close to native s

It runs at 1/10 speed because it's interpreted bytecode, and it allocates a new PyInt object for each number in the loop. You can get it back close to native speed by adding a type annotation and compiling the python file with Cython: http://docs.cython.org/src/userguide/language_basics.html#integer-for-loops http://docs.cython.org/src/userguide/language_basics.html#in... def f(NUMBER): cdef int i for i in range(NUMBER): pass