How to Install mypy-extensions in Python?

by 
pip install mypy-extensions

The Python mypy-extensions library is among the top 100 Python libraries, with more than 22,957,941 downloads. This article will show you everything you need to get this installed in your Python environment.

How to Install mypy-extensions on Windows?

  1. Type "cmd" in the search bar and hit Enter to open the command line.
  2. Type “pip install mypy-extensions” (without quotes) in the command line and hit Enter again. This installs mypy-extensions for your default Python installation.
  3. The previous command may not work if you have both Python versions 2 and 3 on your computer. In this case, try "pip3 install mypy-extensions" or “python -m pip install mypy-extensions“.
  4. Wait for the installation to terminate successfully. It is now installed on your Windows machine.

Here’s how to open the command line on a (German) Windows machine:

Open CMD in Windows

First, try the following command to install mypy-extensions on your system:

pip install mypy-extensions

Second, if this leads to an error message, try this command to install mypy-extensions on your system:

pip3 install mypy-extensions

Third, if both do not work, use the following long-form command:

python -m pip install mypy-extensions

The difference between pip and pip3 is that pip3 is an updated version of pip for Python version 3. Depending on what’s first in the PATH variable, pip will refer to your Python 2 or Python 3 installation—and you cannot know which without checking the environment variables. To resolve this uncertainty, you can use pip3, which will always refer to your default Python 3 installation.

How to Install mypy-extensions on Linux?

You can install mypy-extensions on Linux in four steps:

  1. Open your Linux terminal or shell
  2. Type “pip install mypy-extensions” (without quotes), hit Enter.
  3. If it doesn’t work, try "pip3 install mypy-extensions" or “python -m pip install mypy-extensions“.
  4. Wait for the installation to terminate successfully.

The package is now installed on your Linux operating system.

How to Install mypy-extensions on macOS?

Similarly, you can install mypy-extensions on macOS in four steps:

  1. Open your macOS terminal.
  2. Type “pip install mypy-extensions” without quotes and hit Enter.
  3. If it doesn’t work, try "pip3 install mypy-extensions" or “python -m pip install mypy-extensions“.
  4. Wait for the installation to terminate successfully.

The package is now installed on your macOS.

How to Install mypy-extensions in PyCharm?

Given a PyCharm project. How to install the mypy-extensions library in your project within a virtual environment or globally? Here’s a solution that always works:

  • Open File > Settings > Project from the PyCharm menu.
  • Select your current project.
  • Click the Python Interpreter tab within your project tab.
  • Click the small + symbol to add a new library to the project.
  • Now type in the library to be installed, in your example "mypy-extensions" without quotes, and click Install Package.
  • Wait for the installation to terminate and close all pop-ups.

Here’s the general package installation process as a short animated video—it works analogously for mypy-extensions if you type in “mypy-extensions” in the search field instead:

Make sure to select only “mypy-extensions” because there may be other packages that are not required but also contain the same term (false positives):

How to Install mypy-extensions in a Jupyter Notebook?

To install any package in a Jupyter notebook, you can prefix the !pip install my_package statement with the exclamation mark "!". This works for the mypy-extensions library too:

!pip install my_package

This automatically installs the mypy-extensions library when the cell is first executed.

How to Resolve ModuleNotFoundError: No module named ‘mypy-extensions’?

Say you try to import the mypy-extensions package into your Python script without installing it first:

import mypy-extensions
# ... ModuleNotFoundError: No module named 'mypy-extensions'

Because you haven’t installed the package, Python raises a ModuleNotFoundError: No module named 'mypy-extensions'.

To fix the error, install the mypy-extensions library using “pip install mypy-extensions” or “pip3 install mypy-extensions” in your operating system’s shell or terminal first.

See above for the different ways to install mypy-extensions in your environment.

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