Virtual Environments

In this section you are going to build a virtual environment using python, and then learn how to use an install.sh to automate this process.

Step 1: Verify Python is installed

Open VSCode, and open the terminal and run
Terminal
```
python3 --version
```
Explanation

This command checks if Python 3 is installed on your system. If it returns a version number, you're good to go.

On some systems, you may need to run:
Terminal
```
python --version
```
Tip
You can also use the shell command called... command
```
command -v python
```

Step 2: Create a Virtual Environment

Choose a name for your virtual environment (for example, myenv) and run:
Terminal
```
python3 -m venv myenv
```
This command creates a directory named myenv containing a self-contained Python installation.

Info

Think of this as creating a special folder where all the tools (Python libraries) you use for your project are kept, so they don't interfere with tools for other projects.

Step 3: Activate the Virutal Envionment

Activation is necessary so that when you install packages, they go into this isolated environment rather than your system-wide Python installation.
- Linux/MacOS :
  Terminal
```
source myenv/bin/activate
```
- On Windows (Command Prompt):
  Terminal
```
myenv\Scripts\activate.bat
```
- On Windows (Bash):
  Terminal
```
source myenv/Scripts/activate
```
- On Windows (Powershell):
  Terminal
```
source myenv/Scripts/activate.ps1
```
After activation, your command prompt should change (usually showing the environment name), indicating that you're now working inside myenv

Info

Activating the environment is like stepping into your dedicated workspace where all the tools you install won't mix with others outside of this space.
You can verify by runnning pip list, you should only have one package
Terminal
```
$ pip list
Package Version
------- -------
pip     24.3.1
```

Step 4: Install Packages

Once your virtual environment is activated, you can install any packages you need. For example:
Terminal
```
pip install numpy pandas requests
```
If you later decide to track these dependencies, you can create a requirements.txt file by running:
Terminal
```
pip freeze > requirements.txt
```

Step 5: Deactivate the Virtual Environment

When you’re finished working, simply run:
Terminal
```
deactivate
```
This returns you to your system's default Python environment.

Note

Using virtual environments ensures that your project dependencies remain isolated and consistent across different development environments, a best practice in professional Python development

Step 6: Install.sh

Step 6.1: Initial Setup and OS Detection

Create a new file outside of the venv/ called install.sh
Begin your script with a shebang and error handling, then detect the operating system.
Code
```
#!/usr/bin/env bash
set -e

# Detect the operating system.
OS_TYPE=$(uname -s)
echo "Detected OS: $OS_TYPE"
```
Explanation

The shebang #!/usr/bin/env bash tells your system to run the script with Bash. The set -e command makes the script exit immediately if any command fails. uname -s fetches the OS type.

Step 6.2: Checking for Python Installation

Ensure that Python (preferably Python 3) is installed before proceeding.

Code

# Check if Python 3 is available.
if command -v python3 &> /dev/null; then
    PYTHON=python3
elif command -v python &> /dev/null; then
    PYTHON=python
else
    echo "Python is not installed. Please install Python and try again."
    exit 1
fi

echo "Using Python executable: $PYTHON"

Explanation

This block checks for the presence of python3 or falls back to python. If neither is available, the script exits with an error.

Step 6.3: Creating the Virtual Environment

Define a directory for your virtual environment and create it if it doesn’t already exist.

Code

# Define the directory for the virtual environment.
ENV_DIR="venv"

# Create the virtual environment if it doesn't already exist.
if [ -d "$ENV_DIR" ]; then
    echo "Virtual environment directory '$ENV_DIR' already exists."
else
    echo "Creating virtual environment in '$ENV_DIR'..."
    $PYTHON -m venv "$ENV_DIR"
fi

Explanation

The variable ENV_DIR specifies the folder (named venv) where the virtual environment will be created. The script checks if the folder exists and creates it if not.

Step 6.4: Determining the pip Executable Path

Determine the correct path to the pip executable based on the operating system.

Code

# Determine the correct pip executable based on OS.
if [ "$OS_TYPE" = "Darwin" ] || [ "$OS_TYPE" = "Linux" ]; then
    PIP="$ENV_DIR/bin/pip"
elif [[ "$OS_TYPE" == MINGW* || "$OS_TYPE" == CYGWIN* || "$OS_TYPE" == MSYS* ]]; then
    PIP="$ENV_DIR\\Scripts\\pip.exe"
else
    echo "Unknown OS. Cannot determine pip path."
    exit 1
fi

Explanation

This code sets the PIP variable to point to the correct executable path for pip, depending on whether you’re on Linux/macOS or Windows.

Step 6.5: Installing Packages from requirements.txt

If a requirements.txt file exists in the directory, use it to install pip packages. If you remember we had one from Step 4.

Code

# Check if requirements.txt exists and install the packages if it does.
if [ -f "requirements.txt" ]; then
    echo "Installing pip packages from requirements.txt..."
    $PIP install -r requirements.txt
else
    echo "requirements.txt not found. Skipping package installation."
fi

echo "Pip package installation complete."

Explanation

This block checks for a requirements.txt file and, if found, installs all packages listed in it using pip.

Step 6.6: Displaying Activation Instructions

Provide the user with the correct command to activate the virtual environment

Code

# Provide activation instructions based on the OS.
if [ "$OS_TYPE" = "Darwin" ] || [ "$OS_TYPE" = "Linux" ]; then
    echo "To activate the virtual environment, run:"
    echo "  source $ENV_DIR/bin/activate"
elif [[ "$OS_TYPE" == MINGW* || "$OS_TYPE" == CYGWIN* || "$OS_TYPE" == MSYS* ]]; then
    echo "For Windows, run:"
    echo "  $ENV_DIR\\Scripts\\activate"
else
    echo "Unknown OS. Please activate the virtual environment manually."
fi

echo "Setup complete."

Explanation

The final section outputs the appropriate activation command for the user, depending on their operating system..

Step 6.7: Installer code

install.sh full code

#!/usr/bin/env bash

# Exit immediately if any command fails.
set -e

# Detect the operating system.
OS_TYPE=$(uname -s)
echo "Detected OS: $OS_TYPE"

# Check if Python 3 is available.
if command -v python3 &> /dev/null; then
    PYTHON=python3
elif command -v python &> /dev/null; then
    PYTHON=python
else
    echo "Python is not installed. Please install Python and try again."
    exit 1
fi

echo "Using Python executable: $PYTHON"

# Define the directory for the virtual environment.
ENV_DIR="venv"

# Create the virtual environment if it doesn't already exist.
if [ -d "$ENV_DIR" ]; then
    echo "Virtual environment directory '$ENV_DIR' already exists."
else
    echo "Creating virtual environment in '$ENV_DIR'..."
    $PYTHON -m venv "$ENV_DIR"
fi

# Determine the correct pip executable based on OS.
if [ "$OS_TYPE" = "Darwin" ] || [ "$OS_TYPE" = "Linux" ]; then
    PIP="$ENV_DIR/bin/pip"
elif [[ "$OS_TYPE" == MINGW* || "$OS_TYPE" == CYGWIN* || "$OS_TYPE" == MSYS* ]]; then
    PIP="$ENV_DIR\\Scripts\\pip.exe"
else
    echo "Unknown OS. Cannot determine pip path."
    exit 1
fi

# Check if requirements.txt exists and install the packages if it does.
if [ -f "requirements.txt" ]; then
    echo "Installing pip packages from requirements.txt..."
    $PIP install -r requirements.txt
else
    echo "requirements.txt not found. Skipping package installation."
fi

echo "Pip package installation complete."

# Provide activation instructions based on the OS.
if [ "$OS_TYPE" = "Darwin" ] || [ "$OS_TYPE" = "Linux" ]; then
    echo "To activate the virtual environment, run:"
    echo "  source $ENV_DIR/bin/activate"
elif [[ "$OS_TYPE" == MINGW* || "$OS_TYPE" == CYGWIN* || "$OS_TYPE" == MSYS* ]]; then
    echo "For Windows, run:"
    echo "  $ENV_DIR\\Scripts\\activate"
else
    echo "Unknown OS. Please activate the virtual environment manually."
fi

echo "Setup complete."

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