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Choosing between CPython, Jython, IronPython, PyPy and Cython


The default implementation of the Python programming language is Cpython. It is written in C. It is the original Python version, which users download from its official website,

 CPython has the highest compatibility with a variety of Python packages and modules and is the best choice if users need to write code that completely matches the Python standards.

Cpython compiles the python source code into intermediate bytecode, which is executed by the Cpython virtual machine. CPython is distributed with a large standard library written in a mixture of C and Python. CPython provides the highest level of compatibility with Python packages and C extension modules. 


Jython is an implementation of the Python programming language that can run on the Java platform. Jython compiles to Java bytecode and run in JVM (Java Virtual Machine).

Jython, it is able to call Java functions from Python and Python functions from Java.Jython compiles into Java byte code, which can then be run by Java virtual machine.

Jython allows users to easily work with Java programs since you can call, as well as utilize, your Java functions and classes directly from Jython without any additional effort which is immensely beneficial as Python users can get access into the enormous ecosystem of libraries and frameworks that come along with Java. The same is true on the opposite end.

Jython enables the use of Java class library functions from the Python program. Jython is slow as compared to Cpython and lacks compatibility with CPython libraries.


IronPython is an alternative implementation of the Python programming language, written in C#, designed to run on .NET Framework platform.

It uses .Net Virtual Machine i.e Common Language Runtime. IronPython can use the .NET Framework and Python libraries, and other .NET languages can use Python code very efficiently. 

IronPython excels for programs that make use of threading and can be found on the website.


PyPy is the Python implementation that has been written in the Python language itself and is another alternative to CPython.

If you want your code to run faster, you should probably just use PyPy.Python is dynamic programming language. 

PyPy is an alternative implementation of the Python programming language, written in RPython (Restricted Python). PyPy, your Python program can run faster than with CPython, because PyPy is a JIT (just-in-time) compiler, while CPython is an interpreter.

 Python is said to be slow as the default CPython implementation compiles the python source code in bytecode which is slow as compared to machine code.


Cython is NOT an alternative implementation of the Python programming language, it is a superset of the Python programming language which additionally supports calling C/C++ functions.

Cython is a compiled language that is typically used to generate C extensions (*.pyd on Windows, or *.so on Uinux-like) for Python.

Cython is not a Python interpreter but rather a superset of the Python language that allows users to compile programs in the C language. 

Submitted by devanshi.srivastava on July 22, 2021

Devanshi, is working as a Data Scientist with iVagus. She has expertise in Python, NumPy, Pandas and other data science technologies.


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