Adventures in Machine Learning

Boosting Python Performance with PyPy: A Comprehensive Guide

Introduction to PyPy

Python has been one of the most popular programming languages for over a decade, thanks to its simplicity and versatility. However, there is one area where Python falls short in comparison to languages like C++ and Java: speed.

The traditional CPython implementation of Python has performance limitations that can become a bottleneck in certain applications, especially those that involve heavy computation or dealing with large datasets. This is where PyPy comes in, offering an attractive alternative to CPython that can boost performance significantly.

PyPy is a Python implementation that is written in Python and uses a Just-In-Time (JIT) compiler to execute Python code. This results in faster execution times, making PyPy an interesting option for performance-critical applications.

PyPy is compatible with most Python libraries, so developers can write their code using the same libraries and tools they are familiar with when developing with CPython.

Python and PyPy

Python is an interpreted language, meaning that the code is executed at runtime rather than compiled beforehand. This gives Python a lot of flexibility but comes at the cost of performance.

CPython, the primary implementation of Python, is an interpreted language written in C. Despite its widespread popularity, it has performance limitations due to the overhead of object allocation and frequent method lookups.

PyPy, on the other hand, is an alternative implementation of Python that uses a JIT compiler. Every time a block of code is executed, it is converted to machine code, resulting in faster execution times.

This makes PyPy a viable option for applications that require high performance without sacrificing the ease of development provided by Python. One of the main benefits of PyPy over CPython is its ability to play nicely with existing Python libraries.

PyPy has equal compatibility with most Python libraries, including NumPy and Pandas. This means developers do not have to worry about compatibility issues when choosing PyPy over CPython.

Moreover, PyPys Zero Debug Mode allows developers to execute their code at an even faster pace, making it a preferred choice for large-scale computations. Other features that make PyPy beneficial over CPython include the support for easy-to-use multithreading, as well as compatibility with popular Python libraries written in C like SciPy and Numba.

PyPys Just-In-Time (JIT) compiler design is one of the features that sets it apart from CPython. The JIT compiler identifies code loops that are executed frequently, and dynamically compiles these loops into machine code for faster execution.

This makes PyPy ideal for heavy computation tasks, especially where performance is of utmost importance. CPython, on the other hand, interprets every line of code as it is run, and therefore, cannot dynamically compile loops, leading to slower execution times.

While this difference may not be noticeable in small-scale applications, it becomes a significant bottleneck in large-scale applications requiring heavy computation.


Pythons popularity has grown significantly in recent years, with the language being a go-to option for developers building web, machine learning, or data science projects. However, Pythons performance limitations have been a cause for concern, especially for applications that require high-performance execution.

PyPy has emerged as a viable solution that can boost Pythons execution speeds and make it competitive with other high-performance languages. PyPy’s Just-In-Time (JIT) compilation results in faster execution times, especially for heavy computation tasks, making it an attractive option for developers.

PyPys compatibility with existing Python libraries, along with its support for multithreading and zero-debug mode, has made it a popular choice for high-performance applications. While PyPy may not be suitable for every Python application, it is worth considering for applications where performance is critical.

Its compatibility with most Python libraries and ease of development make it an attractive choice for developers looking to push the limits of what is possible in Python.

PyPy in Action

In this section, we’ll look at a practical example of running a Python script with PyPy and compare its performance with CPython. We’ll also explore some of the features of PyPy that distinguish it from CPython.

Running a Python Script with PyPy

To run a Python script with PyPy, we need to have PyPy installed on our system. PyPy can be installed from the official website ( or through package managers like pip.

Once PyPy is installed, we can run our Python scripts using the PyPy interpreter, instead of CPython. Let’s consider a simple Python script that calculates the factorial of a given number:

def factorial(n):
    if n == 0:
        return 1
        return n * factorial(n-1)


To run this script with PyPy, we can simply enter the following command in the terminal:


The output of the script will be the same regardless of whether we run it with PyPy or CPython, which is `120`.

Performance Comparison between PyPy and CPython

Now, let’s compare the performance of this script when run with PyPy and CPython. We’ll first run it with CPython and measure its execution time using the time module:

import time

start_time = time.time()

def factorial(n):
    if n == 0:
        return 1
        return n * factorial(n-1)


end_time = time.time()
print("Execution Time:", end_time - start_time, "Seconds")

When we run this script with CPython, it takes around 16 seconds to execute. Now, let’s run the same script with PyPy and measure its execution time:

import time

start_time = time.time()

def factorial(n):
    if n == 0:
        return 1
        return n * factorial(n-1)


end_time = time.time()
print("Execution Time:", end_time - start_time, "Seconds")

When we run this script with PyPy, it takes only around 2 seconds to execute. This is a significant improvement in performance compared to CPython.

PyPy and its Features

PyPy’s dynamic language framework is a key feature that distinguishes it from CPython. PyPy is not another implementation of Python but is a Python implementation itself.

PyPy is written in RPython, which is a mixture of Python and C. RPython makes it easier to write interpreters for dynamic languages like Python and Ruby, and it allows the interpreters to be optimized easily.

PyPy’s JIT Compilation

PyPy’s JIT compilation is another feature that sets it apart from CPython. JIT compilation works by identifying blocks of frequently executed code and compiling them to machine code in real-time.

This results in faster execution times compared to pure interpretation. PyPy’s JIT compiler tracks the behavior of the Python program at runtime and optimizes the code on-the-fly.

The JIT compiler is capable of detecting hotspots and optimizing the code accordingly, making the execution time faster than CPython.

Garbage Collection in PyPy

PyPy’s garbage collection is also noteworthy. PyPy uses a generational garbage collector, which is more efficient than CPython’s garbage collector.

The generational garbage collector divides the memory into generations based on the age of the objects in it. Objects that have been around for a while are moved to an older generation, while new objects are kept in the younger generation.

The younger generation is cleaned more frequently than the older generation. This strategy reduces the frequency of garbage collection runs and improves the overall efficiency of the Python program.


PyPy offers an attractive alternative to CPython due to its speed improvements and compatibility with most Python libraries. PyPy’s dynamic language framework allows it to optimize Python code at runtime, making it faster and more efficient than CPython.

PyPy’s JIT compilation and generational garbage collection are some of its key features that make it an attractive option for applications that require high performance and efficient memory management.

Limitations of PyPy

In this section, we’ll take a closer look at some of the limitations of PyPy that developers should be aware of when deciding whether to use PyPy over CPython.

PyPy’s Limitations with C Extensions

One significant limitation of PyPy is its compatibility with C extensions.

PyPy is not as compatible with C extensions as CPython, which can be a problem for developers who rely on third-party C extensions for their Python programs. PyPy can use C extensions, but they may not perform as well or may not work at all, ultimately slowing down the performance of the program.

The reason for this limitation in PyPy is that C Python and PyPy have different internal designs. CPython is written in C, while PyPy is written in Python, so they interact with C extensions differently.

Because of this, it is always a good idea to test your program with PyPy before using it for production and ensure that it works correctly with the Python implementation.

The Performance Overhead of PyPy for Small Scripts

While PyPy can boost performance for computationally complex code, it may not always be the best choice for small scripts. Since PyPy’s JIT compiler takes time to start up, this can lead to a significant overhead for small or short-running scripts.

These small scripts may take longer to run with PyPy due to this initial overhead. For these cases, CPython may perform better as its interpreter is already running and doesn’t take the time to startup.

Therefore, it’s essential to test and benchmark scripts on both PyPy and CPython to choose the best interpreter depending on the nature and size of the Python script.

Lack of Ahead-of-Time Compilation in PyPy

While PyPy’s JIT compiler may lead to significant speed improvements, PyPy does not have ahead-of-time (AOT) compilation support. AOT compilation is preferred in some use cases, where the program needs to be compiled to machine code before it is executed.

For example, ahead-of-time compilation can be useful when creating embedded systems, where speed and performance are vital, and the size of the program needs to be as small as possible. CPython can be used in these cases since it supports ahead-of-time compilation.

PyPy, on the other hand, is not compiled ahead of time, making it less suitable for fully-compiled languages.


PyPy presents an attractive option for developers looking to boost performance in their Python programs. Its dynamic language framework and JIT compiler allow it to optimize and execute code faster than CPython.

However, PyPy has some limitations, such as compatibility with C extensions and overhead when running small scripts, which may impact performance. Additionally, PyPy does not currently support ahead-of-time compilation, making it less suitable for fully-compiled languages.

Therefore, it is essential to test and benchmark your program on both PyPy and CPython to assess the best choice of implementation depending on the problem’s size and complexity. By doing so, developers can use PyPy where performance improvements offer a significant advantage, while at the same time being aware of its limitations.

In this article, we explored PyPy as an alternative to CPython, a primary implementation of Python that can have performance limitations. PyPy, written in a unique dynamic language framework, offers improved performance for computationally complex tasks thanks to its JIT compiler and improved garbage collector.

However, PyPy does have some limitations, such as compatibility with C extensions, overhead when running small scripts, and lack of AOT compilation, which should be taken into consideration when selecting the appropriate Python implementation for a given problem. Overall, developers should test their program on both PyPy and CPython and weigh the benefits and drawbacks of each implementation to ensure the best performance and compatibility in their Python applications.

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