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Porting Open source CPython Encryption Lib to Python 3 - Lessons Learnt

By Ashu Dagar

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OVERVIEW OF THE TALK

Introduction to CPython
Need to convert the CPython extensions
The difference between Python 2.7 and Python3 with CPython
Guidelines to follow for migration of any library
Q&A

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CPython

CPython is the reference implementation of the Python programming language.

Written in C and Python, CPython is the default and most widely-used implementation of the language.

CPython can be defined as both an interpreter and a compiler as it compiles Python code into bytecode before interpreting it.

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Why CPython Extensions

You might be wondering... Python is a fantastic high level language capable of just about anything, why would I want to deal with messy C code?

And I would have to agree with the general premise of that argument. However, there are two common use cases I have found where this is likely to come up:

to speed up a particular slow piece of Python code and,
you are forced to include a program already written in C into an establish Python program and you don't want to rewrite the C code in Python.

The latter happened to me recently and I wanted to share what I've learned with you.

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Differences in Python 2 and 3 with CPython

2to3
Unicode
Exception Handling
xrange
print function

Unicode is the factor which produces the different outputs in CPython.

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Guidelines for Migrating C Extensions

Obtain or write C code
Write Python C API wrapper function
Define function(s) table
Define module
Write initialization function
Package and build the extension