A common error you may encounter when using Python is modulenotfounderror: no module named ‘cv2’. This error occurs when Python cannot detect the OpenCV library in your current environment.
You can install OpenCV using pip as follows:
python3 -m pip install opencv-python
You can install OpenCV using conda as follows:
conda install -c conda-forge opencv
This tutorial goes through the exact steps to troubleshoot this error for the Windows, Mac and Linux operating systems.
Table of contents
ModuleNotFoundError: no module named ‘cv2’
What is ModuleNotFoundError?
The ModuleNotFoundError occurs when the module you want to use is not present in your Python environment. There are several causes of the modulenotfounderror:
The module’s name is incorrect, in which case you have to check the name of the module you tried to import. Let’s try to import the re module with a double e to see what happens:
import ree
--------------------------------------------------------------------------- ModuleNotFoundError Traceback (most recent call last) 1 import ree ModuleNotFoundError: No module named 'ree'
To solve this error, ensure the module name is correct. Let’s look at the revised code:
import re print(re.__version__)
2.2.1
You may want to import a local module file, but the module is not in the same directory. Let’s look at an example package with a script and a local module to import. Let’s look at the following steps to perform from your terminal:
mkdir example_package cd example_package mkdir folder_1 cd folder_1 vi module.py
Note that we use Vim to create the module.py file in this example. You can use your preferred file editor, such as Emacs or Atom. In module.py, we will import the re module and define a simple function that prints the re version:
import re
def print_re_version():
print(re.__version__)
Close the module.py, then complete the following commands from your terminal:
cd ../ vi script.py
Inside script.py, we will try to import the module we created.
import module
if __name__ == '__main__':
mod.print_re_version()
Let’s run python script.py from the terminal to see what happens:
Traceback (most recent call last):
File "script.py", line 1, in ≺module≻
import module
ModuleNotFoundError: No module named 'module'
To solve this error, we need to point to the correct path to module.py, which is inside folder_1. Let’s look at the revised code:
import folder_1.module as mod
if __name__ == '__main__':
mod.print_re_version()
When we run python script.py, we will get the following result:
2.2.1
Lastly, you can encounter the modulenotfounderror when you import a module that is not installed in your Python environment.
What is cv2?
It may be unclear to see cv, cv2, and OpenCV used interchangeably online. OpenCV stands for Open Source Computer Vision Library, and it provides a common infrastructure for computer vision applications. OpenCV is written in C/C++ and has two Python interfaces, CV and CV2. CV2 is the latest Python interface. OpenCV does not come automatically installed with Python. The simplest way to install OpenCV 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 cv2 with both.
How to Install cv2 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
cv2 installation on Windows Using pip and virtualenv
To install cv2, 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 cv2 within the environment by running the following command from the command prompt.
python3 -m pip install opencv-python
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 cv2 on Mac Operating System
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
cv2 installation on Mac Using pip and virtualenv
To install cv2, 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 cv2 within the environment by running the following command from the command prompt.
python3 -m pip install opencv-python
How to Install cv2 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
cv2 installation on Linux Using pip and virtualenv
To install cv2, 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 cv2 within the environment by running the following command from the command prompt.
python3 -m pip install opencv-python
Installing cv2 Using Anaconda
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 Anaconda installed, you can create a conda virtual environment to install cv2.
First, create a conda environment to install cv2.
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 cv2 using conda.
conda install -c conda-forge opencv
Check cv2 Version
Once you have successfully installed cv2, you can use two methods to check the version of cv2. First, you can use pip show from your terminal. Remember that the name of the package is opencv-python.
pip show opencv-python
Name: opencv-python Version: 4.5.5.62 Summary: Wrapper package for OpenCV python bindings.
Second, within your python program, you can import cv2 and then reference the __version__ attribute:
import cv2 print(cv2.__version__)
4.5.5
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 OpenCV.
For further reading on installing data science and machine learning libraries, you can go to the articles:
- Requests: How to Solve Python ModuleNotFoundError: no module named ‘requests’
- Pandas: How to Solve Python ModuleNotFoundError: no module named ‘pandas’
- Matplotlib: How to Solve Python ModuleNotFoundError: no module named ‘matplotlib’
- Pygame: How to Solve Python ModuleNotFoundError: no module named ‘pygame’
- PyTorch: How to Solve Python ModuleNotFoundError: no module named ‘torch’
- openpyxl: How to Solve Python ModuleNotFoundError: no module named ‘openpyxl’
Go to the online courses page on Python to learn more about Python for data science and machine learning.
Have fun and happy researching!