When dealing with cryptographic hashes in Python, you might get the following error:
ModuleNotFoundError: No module named 'Crypto'
This error occurs when Python can’t find the crypto library in the current environment.
In this tutorial, I will show you an example that causes this error and how to fix it in practice.
How to reproduce the error
Suppose you want to use the Crypto module to generate SSH public and private keys as shown below:
from Crypto.PublicKey import RSA
key = RSA.generate(2048)
private_key = key.export_key()
file_out = open("private.pem", "wb")
file_out.write(private_key)
file_out.close()
public_key = key.publickey().export_key()
file_out = open("public.pem", "wb")
file_out.write(public_key)
file_out.close()
But you get the following error when running the code:
Traceback (most recent call last):
File "main.py", line 1, in <module>
from Crypto.PublicKey import RSA
ModuleNotFoundError: No module named 'Crypto'
To my knowledge, the ModuleNotFoundError happens when Python can’t find the module you’re trying to import.
The Crypto module is commonly provided by crypto, pycrypto, or pycryptodome library, and it’s not bundled with Python so you need to install it first.
How to fix this error
To resolve this error, you need to install the pycryptodome library using the pip install command.
If you have crypto or pycrypto library, I suggest you uninstall them first to avoid collisions:
pip uninstall crypto pycrypto
pip install pycryptodome
# For pip3:
pip3 uninstall crypto pycrypto
pip3 install pycryptodome
The pycryptodome library is the most recent and actively maintained library. Once the module is installed, you should be able to run the code that imports Crypto without receiving the error.
Install commands for other environments
The install command might differ depending on what environment you used to run the Python code.
Here’s a list of common install commands in popular Python environments to install the pycryptodome module:
# if you don't have pip in your PATH:
python -m pip install pycryptodome
python3 -m pip install pycryptodome
# Windows
py -m pip install pycryptodome
# Anaconda
conda install pycryptodome
# Jupyter Notebook
!pip install pycryptodome
Once the module is installed, you should be able to run the code without receiving this error.
Other common causes for this error
If you still see the error even after installing the module, it means that the Crypto module can’t be found in your Python environment.
There are several reasons why this error can happen:
- You may have multiple versions of Python installed on your system, and you are using a different version of Python than the one where pycryptodome is installed.
- You might have pycryptodome installed in a virtual environment, and you are not activating the virtual environment before running your code.
- Your IDE uses a different version of Python from the one that has pycryptodome
- The package is not installed in PyCharm
Let’s see how to fix these errors in practice.
1. You have multiple versions of Python
If you have multiple versions of Python installed on your system, you need to make sure that you are using the specific version where the pycryptodome module is available.
You can test this by running the which -a python or which -a python3 command from the terminal:
$ which -a python3
/opt/homebrew/bin/python3
/usr/bin/python3
In the example above, there are two versions of Python installed on /opt/homebrew/bin/python3 and /usr/bin/python3.
Suppose you run the following steps in your project:
- Install pycryptodome with
pipusing/usr/bin/Python version - Install Python using Homebrew, you have Python in
/opt/homebrew/ - Then you run
import Cryptoin your code
The steps above will cause the error because pycryptodome is installed in /usr/bin/, and your code is probably executed using Python from /opt/homebrew/ path.
To solve this error, you need to run the pip install pycryptodome command again so that pycryptodome is installed and accessible by the active Python version.
2. Python virtual environment is active
Another scenario that could cause this error is you may have pycryptodome installed in a virtual environment.
Python venv package allows you to create a virtual environment where you can install different versions of packages required by your project.
If you are installing pycryptodome inside a virtual environment, then the module won’t be accessible outside of that environment.
You can see if a virtual environment is active or not by looking at your prompt in the terminal.
When a virtual environment is active, the name of that environment will be shown inside parentheses as shown below:
In the picture above, the name of the virtual environment (demoenv) appears, indicating that the virtual environment is currently active.
If you run pip install while the virtual environment is active, then the package is installed only for that environment
Likewise, any package installed outside of that virtual environment won’t be accessible from the virtual environment. The solution is to run the pip install command on the environment you want to use.
If you want to install pycryptodome globally, then turn off the virtual environment by running the deactivate command before running the pip install command.
3. IDE using a different Python version
Finally, the IDE from where you run your Python code may use a different Python version when you have multiple versions installed.
For example, you can check the Python interpreter used in VSCode by opening the command palette (CTRL + Shift + P for Windows and ⌘ + Shift + P for Mac) then run the Python: Select Interpreter command.
You should see all available Python versions listed as follows:
You need to use the same version where you installed pycryptodome so that the module can be found when you run the code from VSCode.
Once done, you should be able to import Crypto without receiving any errors.
4. You see this error in PyCharm
If you’re using PyCharm as your IDE, then this error might occur because the package is not installed in the Python interpreter used by PyCharm.
This is because PyCharm creates a new virtual environment for each project you create using the IDE.
To resolve this error, you can install the package using PyCharm’s terminal.
For more information, you can see the guide to install and uninstall packages in PyCharm.
Conclusion
In summary, the ModuleNotFoundError: No module named 'Crypto' occurs when the pycryptodome library is not installed in your Python environment. To resolve this error, you need to run the pip install pycryptodome command.
If you already have the module installed, make sure you are using the correct version of Python, check if the virtual environment is active if you have one, and check for the Python version used by your IDE.
By following these steps, you should be able to import the Crypto module in your code successfully.
I hope you find this tutorial helpful. Until next time! 👋