93. Virtual Environments with virtualenv

Here are 10 Python snippets and examples to demonstrate the use of virtualenv for managing project dependencies and isolated environments:

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1. Creating a Virtual Environment

# Install virtualenv if not already installed
pip install virtualenv

# Create a new virtual environment named "env"
virtualenv env

Creates a virtual environment named env in the current directory.

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2. Activating a Virtual Environment

# On macOS/Linux
source env/bin/activate

# On Windows
env\Scripts\activate

Activates the virtual environment so all installed packages are isolated to it.

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3. Checking Installed Packages in the Virtual Environment

# After activating the environment
pip list

Displays the list of installed packages within the activated virtual environment.

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4. Installing Packages in the Virtual Environment

# Install Flask within the virtual environment
pip install flask

# Check the installed version of Flask
pip show flask

Installs a package, which is isolated to the virtual environment.

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5. Deactivating the Virtual Environment

# Deactivate the virtual environment
deactivate

Returns to the global Python environment by deactivating the virtual environment.

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6. Specifying Python Version for Virtual Environment

# Create a virtual environment using a specific Python version
virtualenv -p python3.9 env

Specifies a Python version to use in the virtual environment.

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7. Freezing Dependencies

# Generate a requirements.txt file with all installed packages
pip freeze > requirements.txt

Creates a requirements.txt file listing all installed dependencies.

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8. Installing Dependencies from a File

# Install packages listed in requirements.txt
pip install -r requirements.txt

Installs dependencies in bulk from a requirements.txt file.

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9. Using Virtualenvwrapper for Better Management

# Install virtualenvwrapper
pip install virtualenvwrapper

# Export environment variable (Add to .bashrc/.zshrc)
export WORKON_HOME=~/Envs

# Create a virtual environment
mkvirtualenv myenv

# Activate a virtual environment
workon myenv

# Deactivate the virtual environment
deactivate

Enhances virtualenv with features like global environment storage and named environment switching.

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10. Deleting a Virtual Environment

# Remove the virtual environment directory
rm -rf env

Deletes the env directory to completely remove the virtual environment.

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Why Use virtualenv?

• Isolation: Keeps dependencies for each project separate.

• Reproducibility: Ensures consistent environments across machines.

• Python Version Control: Easily create environments with specific Python versions.

• Dependency Management: Simplifies dependency installation and freezing.

These examples provide the essential commands and workflows for using virtualenv effectively in Python projects.