Tutorial

Calling C Functions from Python

Published on August 3, 2022
author

Pankaj

Calling C Functions from Python

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We can call a C function from Python program using the ctypes module.

Calling C Function from Python

It involves the following steps:

  1. Creating a C file (.c extension) with the required functions
  2. Creating a shared library file (.so extension) using the C compiler.
  3. In the Python program, create a ctypes.CDLL instance from the shared file.
  4. Finally, call the C function using the format {CDLL_instance}.{function_name}({function_parameters}).

Step 1: Creating a C File with some functions

#include <stdio.h>

int square(int i) {
	return i * i;
}

We have a simple C function that will return the square of an integer. I have saved this function code in the file named my_functions.c.

Step 2: Creating the Shared Library File

We can use the following command to create the shared library file from the C source file.

$ cc -fPIC -shared -o my_functions.so my_functions.c
C File Shared Library File
C File and Shared Library File

Step 3: Calling C Function from Python Program

>>> from ctypes import *
>>> so_file = "/Users/pankaj/my_functions.so"
>>> my_functions = CDLL(so_file)
>>> 
>>> print(type(my_functions))
<class 'ctypes.CDLL'>
>>> 
>>> print(my_functions.square(10))
100
>>> print(my_functions.square(8))
64
>>> 
Calling C Function From Python
Calling C Function From Python

If you change the C program file, you will have to regenerate the shared library file.

Conclusion

The python default implementation is written in C programming and it’s called CPython. So it’s not very uncommon to use C functions in a python program. In this tutorial, we learned how to easily call C functions in a python program.

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Pankaj

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JournalDev
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December 22, 2021

It does not work properly. Give rise to certain errors.

- shah sawood

    JournalDev
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    September 24, 2021

    I found this helpfull. Thankyou very much

    - Adanech Alemu

      JournalDev
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      September 9, 2021

      What if my C file includes some other custom C library? It seems that the resulting .so file doesn’t include them.

      - Mauro

        JournalDev
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        July 2, 2021

        This was very helpful, thank you a lot, my guy!

        - Itachi Uchiha

          JournalDev
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          March 1, 2021

          it doesnt return the intteger that I defined in C file, It does net get a value by using scanf in C program.d

          - Armagan

            JournalDev
            DigitalOcean Employee
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            February 13, 2021

            doesn’t work. Traceback (most recent call last): File “”, line 1, in TypeError: ‘LibraryLoader’ object is not callable

            - m j

              JournalDev
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              July 22, 2020

              is it possible to connect EM-18 RFID Reader to raspberry pi direct without using RS232 USB adapter? Help me please Sir.

              - Jean Baptiste

                JournalDev
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                January 7, 2020

                how can i run cmake commands using python. Eg: I have a folder with .c files in it and they are linked using CMakeList.txt I do compile them using “cmake -H. -Bbuild” commands I need to put the above command in python script and run the .py directly to build the c files.can anyone help me

                - Keerthana

                  JournalDev
                  DigitalOcean Employee
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                  December 27, 2019

                  Hi Pankaj, Is it possible to call functions in Linux c executable (not . so file) from python?

                  - Manomugdha Biswas

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