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How to Call a C function in Python

  • Difficulty Level : Hard
  • Last Updated : 12 Apr, 2021
Geek Week

Have you ever came across the situation where you have to call C function using python? This article is going to help you on a very basic level and if you have not come across any situation like this, you enjoy knowing how it is possible.
First, let’s write one simple function using C and generate a shared library of the file. Let’s say file name is function.c. 


int myFunction(int num)
    if (num == 0)
        // if number is 0, do not perform any operation.
        return 0;
        // if number is power of 2, return 1 else return 0
          return ((num & (num - 1)) == 0 ? 1 : 0) ;

Compile this : 

cc -fPIC -shared -o function.c

Using ctypes(foreign function interface) library to call C function from Python

The above statement will generate a shared library with the name Now, let’s see how to make use of it in python. In python, we have one library called ctypes. Using this library we can use C function in python. 
Let’s say file name is 


import ctypes
NUM = 16     
# libfun loaded to the python file
# using fun.myFunction(),
# C function can be accessed
# but type of argument is the problem.
fun = ctypes.CDLL("") # Or full path to file 
# Now whenever argument
# will be passed to the function                                                       
# ctypes will check it.
fun.myFunction.argtypes = [ctypes.c_int]
# now we can call this
# function using instant (fun)
# returnValue is the value
# return by function written in C
# code
returnVale = fun.myFunction(NUM)       

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