How to fix the error ModuleNotFoundError: No module named ‘Cython’ in Python

ModuleNotFoundError: No module named 'Cython' in Python

Python is an increasingly popular programming language, and Cython is an extension that makes it especially simple to write high-performance, low-level code. If you’re having trouble with the ModuleNotFoundError: No module named ‘Cython’ in Python, read on for possible solutions.

What is Cython?

Cython is a programming language that enables writing code that interacts seamlessly with Python. It is frequently used to optimize existing Python code or for time-critical applications.

What causes ModuleNotFoundError: No module named ‘Cython’ in Python, and how to fix it?

Some of the most common causes of this error and their solutions are listed below. Let’s examine them and apply them to your situation.

Cython is not installed

Python will throw a ModuleNotFoundError if you attempt to import a module that does not exist. The ModuleNotFoundError: No module named ‘Cython’ occurs because your system has no module named Cython.

In the example below, we imported Cython without first installing it.

# Cython is imported but not installed
import Cython

# Try to get the Cython version

So we get the following error:

ModuleNotFoundError: No module named 'Cython'

To fix this error, ensure that you have Cython installed. If not, use your favorite package manager to install it (e.g., pip).

Pip makes it easier than ever to install Python modules; to install Cython using pip, open your Terminal and type:

pip install Cython

If you’re using Python3 on Linux or macOS, type:

pip3 install Cython

If you see the message “Successfully installed Cython“, it means you installed Cython successfully. Now, you can use Cython without any errors. For example:

# Import after installing Cython
import Cython

# Get the Cython version



The Python interpreter cannot find Cython

This error can occur if your current interpreter is unable to locate Cython. For example, if you’re using Python 3.11 on your computer and, for some reason, need to switch to the Python 3.9 interpreter, when you go to install Cython, it will be installed into Python 3.11. As a result, the Python 3.9 interpreter will fail to locate Cython.

# Install Cython in Python 3.11, but use Cython in Python 3.9
import Cython

# Try to get the Cython version


ModuleNotFoundError: No module named 'Cython'

In this case, simply switch back to the Python 3.11 interpreter, and you’re done. We’ll show you how to switch the Python interpreter in VScode. You can do the same thing with other IDE.

To begin, launch VScode and press Ctrl + Shift + P (Command + Shift + P on macOS).

When the Command Palette appears, type “Python: Select Interpreter“.

Finally, choose the Python interpreter with Cython installed (in our case, Python 3.11). As shown below:

Let’s run the code below to see what happens.

# Use Cython in Python 3.11
import Cython
import sys

# Get the Python version
print('Python version:', sys.version)

# Get the Cython version
print('Cython version:', Cython.__version__)


Python version: 3.11.0
Cython version: 0.29.32


If you get the ModuleNotFoundError: No module named ‘Cython’ in Python, it’s because Cython isn’t installed on your system. There are several ways to fix this error, but the simplest is to install Cython using pip. Once Cython is installed, you should be able to import it into your Python code without any problems. We hope this article helped you fix this error. If you have any questions or comments, please leave them below.

Have a nice day!

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