I'm currently using Python 3.7 and Pycharm for my work. Recently I got a code that is done at Python2.7

You shouldn't use Python 3.7 to run code that was written for Python 2.x, unless you can port that code to Python 3, or you know that it works fine. There are some caveats, and it depends on what the functionality of that code is. In some cases it might be very time consuming to convert it. 2to3 might help here.

So, depending on your use case, you may want to keep a legacy version of Python 2.7 around on your system to run that particular code, but note that Python 2.x will not get any (security) updates anymore, so you're better off using Python 3 from now on.

Try running the code in Python 3.7 and see if it works.

and it includes a library named 'ctypes.'

This is included by default in Python, so you don't need to install anything. Assuming you have the correct Python 2.7 interpreter and all other required packages, the code should just run fine as-is.

If the person who wrote the code was doing a good job, he or she should have left a README and/or a requirements.txt file or something similar that would specify which other packages or libraries are needed to run it.

For those who hit this issue and have root access, you may be able to correct by following the instructions below. Otherwise, you may need to contact your Sys Admin.

The issue is likely a missing installation of libffi-dev which can be installed with:

sudo apt install libffi-dev

Note: You may need to uninstall and re-install python to get this to work. In my case, It would not stick until I re-installed.

Installing libffi-dev and re-installing python3.7 fixed the problem for me.

to cleanly build py 3.7 libffi-dev is required or else later stuff will fail

If using RHEL/Fedora:

sudo yum install libffi-devel

or

sudo dnf install libffi-devel

If using Debian/Ubuntu:

sudo apt-get install libffi-dev

ctypes is a built in library (I think from python2.5) This means you dont need to install it, it is coming built in when you install python.

As far as using the correct version, see the pyenv module - it will make sure you are running the correct python version, and IMO makes life much easier

You don't need to install ctypes at all; it is part of the Python standard library, as of Python 2.5 onwards. See the module documentation.

ctypes 1.0.2 is ancient, don't use it. It was written for Python 2.3 and 2.4 and was never adjusted to run on Python 3, which is why you get the syntax error. You got the errors with Python 2 because you are missing the Python development headers (provided by the python-devel RPM).

Here's a quick and dirty ctypes tutorial.

First, write your C library. Here's a simple Hello world example:

testlib.c

#include <stdio.h>

void myprint(void);

void myprint()
{
    printf("hello world\n");
}

Now compile it as a shared library (mac fix found here):

$ gcc -shared -Wl,-soname,testlib -o testlib.so -fPIC testlib.c

# or... for Mac OS X 
$ gcc -shared -Wl,-install_name,testlib.so -o testlib.so -fPIC testlib.c

Then, write a wrapper using ctypes:

testlibwrapper.py

import ctypes

testlib = ctypes.CDLL('/full/path/to/testlib.so')
testlib.myprint()

Now execute it:

$ python testlibwrapper.py

And you should see the output

Hello world
$

If you already have a library in mind, you can skip the non-python part of the tutorial. Make sure ctypes can find the library by putting it in /usr/lib or another standard directory. If you do this, you don't need to specify the full path when writing the wrapper. If you choose not to do this, you must provide the full path of the library when calling ctypes.CDLL().

This isn't the place for a more comprehensive tutorial, but if you ask for help with specific problems on this site, I'm sure the community would help you out.

PS: I'm assuming you're on Linux because you've used ctypes.CDLL('libc.so.6'). If you're on another OS, things might change a little bit (or quite a lot).