The line `if __name__ == ‘__main__’:` is a common Python idiom that is used to check whether a Python script is being run directly by the Python interpreter or if it is being imported as a module into another script. It allows you to control the execution of code based on how the script is being used.
Here’s an explanation of how it works:
1. `__name__` is a built-in variable in Python that is automatically set by the Python interpreter for every script or module.
2. When a Python script is executed, the `__name__` variable is set to `’__main__’` if the script is the main entry point for the program. In other words, it’s set to `’__main__’` when you run the script directly using the `python` command.
3. If the script is being imported as a module into another script, the `__name__` variable is set to the name of the module (i.e., the filename without the “.py” extension).
The `if __name__ == ‘__main__’:` construct is typically used to define code that should only run when the script is executed directly, not when it’s imported as a module. This is commonly used for script initialization and testing code.
In the context of a Flask application, the code block `if __name__ == ‘__main__’:` is used to ensure that the `app.run(debug=True)` line is executed only when you run the Flask application directly from the command line. When the script is imported into another script or module, the `app.run` line is not executed.
Here’s how it works in a Flask application:
python
from flask import Flask
app = Flask(__name__)
# Define your routes and other application code here
if __name__ == '__main__':
app.run(debug=True)
In this example, the `app.run(debug=True)` line will only execute when you run this script directly (e.g., `python app.py`). If you import this script into another Python script, the `app.run` line won’t execute, which is desirable because you typically don’t want to start the Flask development server when importing a module.