ModuleNotFoundError: No module named 'Cython' in Python

# "ModuleNotFoundError: No module named 'Cython' in Python"

The Python "ModuleNotFoundError: No module named 'Cython'" occurs when we forget to install the Cython module before importing it or install it in an incorrect environment.

To solve the error, install the module by running the pip install Cython command.

Open your terminal in your project's root directory and install the Cython module.

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# 👇️ In a virtual environment or using Python 2
pip install Cython

# 👇️ For Python 3 (could also be pip3.10 depending on your version)
pip3 install Cython

# 👇️ If you get a permissions error
sudo pip3 install Cython
pip install Cython --user

# 👇️ If you don't have pip in your PATH environment variable
python -m pip install Cython

# 👇️ For Python 3 (could also be pip3.10 depending on your version)
python3 -m pip install Cython

# 👇️ Using py alias (Windows)
py -m pip install Cython

# 👇️ For Anaconda
conda install -c anaconda cython

# 👇️ For Jupyter Notebook
!pip install Cython

After you install the Cython package, try importing it like:

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from Cython.Build import cythonize

print(dir(cythonize))

# Common causes of the error

The error occurs for multiple reasons:

1. Not having the Cython package installed by running pip install Cython.
2. Installing the package in a different Python version than the one you're using.
3. Installing the package globally and not in your virtual environment.
4. Your IDE running an incorrect version of Python.
5. Naming your module Cython.py which would shadow the official module.
6. Declaring a variable named Cython which would shadow the imported variable.

If the error persists, get your Python version and make sure you are installing the package using the correct Python version.

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python --version

For example, my Python version is 3.10.4, so I would install the Cython package with pip3.10 install Cython.

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pip3.10 install Cython

# 👇️ If you get a permissions error use pip3 (NOT pip3.X)
sudo pip3 install Cython

Notice that the version number corresponds to the version of pip I'm using.

If the PATH for pip is not set up on your machine, replace pip with python3 -m pip:

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# 👇️ Make sure to use your version of Python, e.g. 3.10
python3 -m pip install Cython

If the "No module named 'Cython'" error persists, try restarting your IDE and development server/script.

# Check if the package is installed

You can check if you have the Cython package installed by running the pip show Cython command.

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# 👇️ Check if you have Cython installed
pip show Cython

# 👇️ If you don't have pip set up in PATH
python -m pip show Cython

The pip show Cython command will either state that the package is not installed or show a bunch of information about the package, including the location where the package is installed.

# Make sure your IDE is using the correct Python version

If the package is not installed, make sure your IDE is using the correct version of Python.

For example, In VSCode, you can press CTRL + Shift + P or (⌘ + Shift + P on Mac) to open the command palette.

Then type "Python select interpreter" in the field.

Then Select the correct Python version from the dropdown menu.

# Install the package in a Virtual Environment

If you are using a virtual environment, make sure you are installing Cython in your virtual environment and not globally.

You can try creating a virtual environment if you don't already have one.

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# 👇️ Use the correct version of Python when creating VENV
python3 -m venv venv

# 👇️ Activate on Unix or MacOS
source venv/bin/activate

# 👇️ Activate on Windows (cmd.exe)
venv\Scripts\activate.bat

# 👇️ Activate on Windows (PowerShell)
venv\Scripts\Activate.ps1

# 👇️ Install Cython in your virtual environment
pip install Cython

If the python3 -m venv venv command doesn't work, try the following 2 commands:

• python -m venv venv
• py -m venv venv

Your virtual environment will use the version of Python that was used to create it.

You also shouldn't be declaring a variable named Cython as that would also shadow the original module.

# Try reinstalling the package

If the error is not resolved, try to uninstall the Cython package and then reinstall it.

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# 👇️ Check if you have Cython installed
pip show Cython

# 👇️ If you don't have pip set up in PATH
python -m pip show Cython

# 👇️ Uninstall Cython
pip uninstall Cython

# 👇️ If you don't have pip set up in PATH
python -m pip uninstall Cython

# 👇️ Install Cython
pip install Cython

# 👇️ If you don't have pip set up in PATH
python -m pip install Cython

Try restarting your IDE and development server/script.

You can also try to upgrade the version of the Cython package.

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pip install Cython --upgrade

# 👇️ If you don't have pip set up in PATH
python -m pip install Cython --upgrade

# Table of Contents

1. Install Cython on Windows
2. Install Cython on macOS or Linux
3. Install Cython in Visual Studio Code
4. Install Cython in PyCharm
5. Install Cython in Anaconda
6. Install Cython in Jupyter Notebook

# Install Cython on Windows

To install the Cython module on Windows:

1. Type CMD in the search bar and open the Command Prompt application.
2. Type pip install Cython and press Enter.

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pip install Cython

# 👇️ For Python 3
pip3 install Cython

# 👇️ If you don't have pip in your PATH environment variable
python -m pip install Cython

# 👇️ For Python 3
python3 -m pip install Cython

# 👇️ Using py alias
py -m pip install Cython

# 👇️ If you get a permissions error
pip install Cython --user

# 👇️ For Anaconda
conda install -c anaconda cython

If the command doesn't succeed, try running CMD as an administrator.

If you get the error 'pip' is not recognized as an internal or external command, use the python -m command when installing Cython.

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python -m pip install Cython

python3 -m pip install Cython

py -m pip install Cython

Alternatively, you can install the Cython module in a virtual environment:

1. Open the root directory of your project.
2. Press Shift and right-click in Explorer.

3. Click on "Open PowerShell window here".
4. Run the following commands.

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# 👇️ Might also be: "python3 -m venv venv"
python -m venv venv

# 👇️ Activate on Windows (PowerShell)
venv\Scripts\Activate.ps1

# 👇️ Activate on Windows (cmd.exe)
venv\Scripts\activate.bat

# 👇️ Install Cython in your virtual environment
pip install Cython

If the python -m venv venv command doesn't work, try the following 2 commands:

• python3 -m venv venv
• py -m venv venv.

If you see an error message that ps1 cannot be loaded because running scripts is disabled on this system, run the following command, type "yes" when prompted and rerun the activation command.

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Set-ExecutionPolicy RemoteSigned -Scope CurrentUser

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pip show Cython
pip3 show Cython

python -m pip show Cython
python3 -m pip show Cython

The pip show Cython command will either state that the package is not installed or show a bunch of information about the package, including the location where the package is installed.

# Install Cython on macOS or Linux

To install Cython on macOS or Linux:

1. Search for "terminal" and start the application.
2. Type pip install Cython and press Enter.

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pip install Cython

# 👇️ For Python 3
pip3 install Cython

# 👇️ If you get a permissions error
sudo pip3 install Cython

# 👇️ If you don't have pip in your PATH environment variable
python -m pip install Cython

# 👇️ For Python 3
python3 -m pip install Cython

# 👇️ Alternative if you get a permissions error
pip install Cython --user

# 👇️ For Anaconda
conda install -c anaconda cython

If you get an error that pip isn't found, use the python -m command.

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python -m pip install Cython

python3 -m pip install Cython

If you get a permissions error, prefix the command with sudo.

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sudo pip install Cython

sudo pip3 install Cython

Alternatively, you can install the Cython package in a virtual environment:

1. Open your terminal in the root directory of your project.
2. Run the following commands.

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# 👇️ Could also be "python -m venv venv"
python3 -m venv venv

# 👇️ Activate virtual env on macOS or Linux
source venv/bin/activate

# 👇️ Install Cython in your virtual environment
pip install Cython

Your virtual environment will use the version of Python that was used to create it.

You can use the pip show command to verify Cython has been installed successfully.

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pip show Cython
pip3 show Cython

python -m pip show Cython
python3 -m pip show Cython

The pip show Cython command will either state that the package is not installed or show a bunch of information about the package.

# Install Cython in Visual Studio Code

To install Cython in Visual Studio Code:

1. Press CTRL + ` (Backtick) on your keyboard to open the terminal.
2. Run the pip install Cython command to install the Cython module.

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pip install Cython

# 👇️ For Python 3
pip3 install Cython

# 👇️ If you get a permissions error
sudo pip3 install Cython

# 👇️ If you don't have pip in your PATH environment variable
python -m pip install Cython

# 👇️ For Python 3
python3 -m pip install Cython

# 👇️ Using py alias
py -m pip install Cython

# 👇️ Alternative if you get a permissions error
pip install Cython --user

When installing Python modules in Visual Studio code, make sure that your IDE is configured to use the correct Python version.

Press CTRL+Shift+P or (⌘ + Shift + P on Mac) to open the command palette.

Then type "Python select interpreter" in the field.

Then Select the correct Python version from the dropdown menu.

You can use the python --version command if you need to get your version of Python.

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python --version
python3 --version

You can also try creating a virtual environment if you don't already have one.

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# 👇️ Could also be "python -m venv venv" or "py -m venv venv"
python3 -m venv venv

# 👇️ Activate on Unix or MacOS
source venv/bin/activate

# 👇️ Activate on Windows (cmd.exe)
venv\Scripts\activate.bat

# 👇️ Activate on Windows (PowerShell)
venv\Scripts\Activate.ps1

# 👇️ Install Cython in your virtual environment
pip install Cython

Your virtual environment will use the version of Python that was used to create it.

# Install Cython in PyCharm

To install Cython in PyCharm:

1. Press Alt+F12 on your keyboard to open the terminal.
2. Run the pip install Cython command to install the Cython module.

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pip install Cython

# 👇️ For Python 3
pip3 install Cython

# 👇️ If you get a permissions error
sudo pip3 install Cython

# 👇️ If you don't have pip in your PATH environment variable
python -m pip install Cython

# 👇️ For Python 3
python3 -m pip install Cython

# 👇️ Using py alias
py -m pip install Cython

# 👇️ Alternative if you get a permissions error
pip install Cython --user

Alternatively, you can use the IDE itself to install the module.

1. Click on "File" > "Settings" > "Project" > "Python Interpreter".
2. Click on the + icon and type Cython.
3. Click on "Install Package".

Click on "File" > "Settings" > "Project" > "Python Interpreter".

Then Select the correct Python version from the dropdown menu.

You can use the python --version command if you need to get your version of Python.

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python --version
python3 --version

# Install Cython in Anaconda

To install Cython in Anaconda:

1. Open your Anaconda Navigator.
2. Click on "Environments" and select your project.
3. Type Cython in the search bar to the right.
4. Tick the Cython package and click on "Apply".

Alternatively, you can install the Cython package with a command.

If you are on Windows, search for "Anaconda Prompt" and open the application.

If you are on macOS or Linux, open your terminal.

Run the following command to install the Cython package.

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# 👇️ Using conda
conda install -c anaconda cython

# 👇️ Alternatively use `pip`
pip install Cython

# 👇️ For Python 3
pip3 install Cython

# 👇️ If you get a permissions error
sudo pip3 install Cython

# 👇️ If you don't have pip in your PATH environment variable
python -m pip install Cython

# 👇️ For Python 3
python3 -m pip install Cython

# 👇️ Using py alias
py -m pip install Cython

# 👇️ Alternative if you get a permissions error
pip install Cython --user

Click on the following article if you need to install a specific version of the package using Anaconda.

# Install Cython in Jupyter Notebook

To install Cython in Jupyter Notebook:

1. Open your terminal and type "jupyter notebook".

2. Click on "New" and then "Terminal" in the browser tab.

3. Type pip install Cython and press Enter.

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# 👇️ Using pip
pip install Cython

# 👇️ For Python 3
pip3 install Cython

# 👇️ If you get a permissions error
sudo pip3 install Cython

# 👇️ If you don't have pip in your PATH environment variable
python -m pip install Cython

# 👇️ For Python 3
python3 -m pip install Cython

# 👇️ Using py alias
py -m pip install Cython

# 👇️ Using conda
conda install -c anaconda cython

# 👇️ Alternative if you get a permissions error
pip install Cython --user

Alternatively, you can use the Python ipykernel.

1. Open your terminal and type "jupyter notebook".

2. Click on "New" and then click on "Python 3 (ipykernel)".

3. Type !pip install Cython and click on "Run".

Note that the pip install command must be prefixed with an exclamation mark if you use this approach.

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!pip install Cython

Once you type the command, click "Run" to install the Cython module.

If you get a permissions error, e.g. "[WinError: 5] Access is denied", add the --user option to the installation command.

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!pip install Cython --user

If the error persists, try to restart the Jupyter Kernel and rerun the command.