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

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

PyCrypto is no longer maintained and should not be used. You should use PyCryptodome, which is a maintained and upgraded fork of PyCrypto. Most applications that depend on PyCrypto will run unmodified

You can install PyCryptodome in Python 3 with python -m pip install pycryptodome.

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


ModuleNotFoundError: no module named ‘Crypto’

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 PyCrypto?

PyCrypto is a Python cryptography toolkit and contains a collection of modules for implementing various cryptographic algorithms and protocols including Cipher and Hash.

PyCrypto is no longer maintained and should not be used. You should use PyCryptodome, which is a maintained and upgraded fork of PyCrypto. Most applications that depend on PyCrypto will run unmodified

The simplest way to install PyCryptodome 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 using 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 PyCryptodome with both.

How to Install PyCryptodome 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

PyCryptodome installation on Windows Using pip

To install PyCryptodome, 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 PyCryptodome within the environment by running the following command from the command prompt.

python3 -m pip install pycryptodome

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.

If you are still getting a No module named Crypto error, check if you have previously installed PyCrypto using pip. You will need to uninstall it and your new install of PyCryptodome as follows:

python3 -m pip uninstall crypto

python3 -m pip uninstall pycryptodome

python3 -m pip install pycryptodome

How to Install PyCryptodome 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 PyCryptodome, 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 Django within the environment by running the following command from the command prompt.

python3 -m pip install pycryptodome

How to Install PyCryptodome 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

PyCryptodome installation on Linux with Pip

To install PyCryptodome, 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 PyCryptodome within the environment by running the following command from the command prompt.

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

python3 -m pip install pycryptodome

Installing PyCryptodome 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 installed Anaconda, you can create a virtual environment and install PyCryptoDome.

To create a conda environment, you can use the following command:

conda create -n crypto python=3.8

You can specify a different Python 3 version if you like. Ideally, choose the latest version of Python. Next, you will activate the project container. You will see “crypto” in parentheses next to the command line prompt.

source activate crypto

Now you’re ready to install PyCryptodome using conda.

Once you have activated your conda environment, you can install PyCryptodome using the following command:

conda install -c conda-forge pycryptodome

Check PyCryptodome Version

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

python3 -m pip show pycryptodome
Name: pycryptodome
Version: 3.14.1
Summary: Cryptographic library for Python

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

import Crypto
print(Crypto.__version__)
4.0.2

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

conda list -f pycryptodome
# Name                    Version                   Build  Channel
pycryptodome              3.14.1           py38hd9741ba_0    conda-forge

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 PyCryptoDome.

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!