A common error you may encounter when using Python is modulenotfounderror: no module named ‘yaml’.

This error occurs when the Python interpreter cannot detect the PyYAML library in your current environment.

You can install PyYAML in Python 3 with python3 -m pip install pyyaml.

This tutorial goes through the exact steps to troubleshoot this error for the Windows, Mac and Linux operating systems.


ModuleNotFoundError: no module named ‘yaml’

What is PyYAML?

YAML is a data serialization format designed for human readability and interaction with scripting languages. PyYAML is a YAML parser and emitter for Python.

The simplest way to install PyYAML is to use the package manager for Python called pip. The following installation instructions are for the major Python version 3.

Always Use a Virtual Environment to Install Packages

It is always best to install new libraries within a virtual environment. You should not install anything into your global Python interpreter when you develop locally. You may introduce incompatibilities between packages, or you may break your system if you install an incompatible version of a library that your operating system needs. Using a virtual environment helps compartmentalize your projects and their dependencies. Each project will have its environment with everything the code needs to run. Most ImportErrors and ModuleNotFoundErrors occur due to installing a library for one interpreter and trying to use the library with another interpreter. Using a virtual environment avoids this. In Python, you can use virtual environments and conda environments. We will go through how to install PyYAML with both.

How to Install PyYAML on Windows Operating System

First, you need to download and install Python on your PC. Ensure you select the install launcher for all users and Add Python to PATH checkboxes. The latter ensures the interpreter is in the execution path. Pip is automatically on Windows for Python versions 2.7.9+ and 3.4+.

You can check your Python version with the following command:

python3 --version

You can install pip on Windows by downloading the installation package, opening the command line and launching the installer. You can install pip via the CMD prompt by running the following command.

python get-pip.py

You may need to run the command prompt as administrator. Check whether the installation has been successful by typing.

pip --version

PyYAML installation on Windows Using pip

To install PyYAML, first create the virtual environment. The environment can be any name, in this we choose “env”:

virtualenv env

You can activate the environment by typing the command:

env\Scripts\activate

You will see “env” in parenthesis next to the command line prompt. You can install PyYAML within the environment by running the following command from the command prompt.

python3 -m pip install pyyaml

We use python -m pip to execute pip using the Python interpreter we specify as Python. Doing this helps avoid ImportError when we try to use a package installed with one version of Python interpreter with a different version. You can use the command which python to determine which Python interpreter you are using.

How to Install PyYAML on Mac Operating System using pip

Open a terminal by pressing command (⌘) + Space Bar to open the Spotlight search. Type in terminal and press enter. To get pip, first ensure you have installed Python3:

python3 --version
Python 3.8.8

Download pip by running the following curl command:

curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py

The curl command allows you to specify a direct download link. Using the -o option sets the name of the downloaded file.

Install pip by running:

python3 get-pip.py

To install PyYAML, first create the virtual environment:

python3 -m venv env

Then activate the environment using:

source env/bin/activate 

You will see “env” in parenthesis next to the command line prompt. You can install PyYAML within the environment by running the following command from the command prompt.

python3 -m pip install pyyaml

How to Install PyYAML on Linux Operating Systems

All major Linux distributions have Python installed by default. However, you will need to install pip. You can install pip from the terminal, but the installation instructions depend on the Linux distribution you are using. You will need root privileges to install pip. Open a terminal and use the commands relevant to your Linux distribution to install pip.

Installing pip for Ubuntu, Debian, and Linux Mint

sudo apt install python-pip3

Installing pip for CentOS 8 (and newer), Fedora, and Red Hat

sudo dnf install python-pip3

Installing pip for CentOS 6 and 7, and older versions of Red Hat

sudo yum install epel-release

sudo yum install python-pip3

Installing pip for Arch Linux and Manjaro

sudo pacman -S python-pip

Installing pip for OpenSUSE

sudo zypper python3-pip

PyYAML installation on Linux with Pip

To install PyYAML, first create the virtual environment:

python3 -m venv env

Then activate the environment using:

source env/bin/activate 

You will see “env” in parenthesis next to the command line prompt. You can install PyYAML within the environment by running the following command from the command prompt.

Once you have activated your virtual environment, you can install PyYAML using:

python3 -m pip install pyyaml

Installing PyYAML Using Anaconda

First, to create a conda environment to install PyYAML.

conda create -n project python=3.6 

Then activate the project container. You will see “project” in parentheses next to the command line prompt.

source activate project

Now you’re ready to install PyYAML using conda.

Anaconda is a distribution of Python and R for scientific computing and data science. You can install Anaconda by going to the installation instructions. Once you have installed Anaconda and created your conda environment, you can install PyYAML using the following command:

conda install -c anaconda pyyaml

Check PyYAML Version

Once you have successfully installed PyYAML, you can check its version. If you used pip to install PyYAML, you can use pip show from your terminal.

python3 -m pip show pyyaml
Name: PyYAML
Version: 5.4.1
Summary: YAML parser and emitter for Python

Second, within your python program, you can import PyYAML and then reference the __version__ attribute:

import yaml
print(yaml.__version__)
5.4.1

If you used conda to install PyYAML, you could check the version using the following command:

conda list -f pyyaml
# Name                    Version                   Build  Channel
pyyaml                    5.3.1            py36haf1e3a3_1    anaconda

Summary

Congratulations on reading to the end of this tutorial. The modulenotfounderror occurs if you misspell the module name, incorrectly point to the module path or do not have the module installed in your Python environment. If you do not have the module installed in your Python environment, you can use pip to install the package. However, you must ensure you have pip installed on your system. You can also install Anaconda on your system and use the conda install command to install PyYAML.

Go to the online courses page on Python to learn more about Python for data science and machine learning.

For further reading on missing modules in Python, go to the article:

Have fun and happy researching!