1: Command Line Python(Command line Python scripting)

We looked at the command line Python interpreter in the last mission. The interpreter lets you run Python commands and see their results immediately. It's very useful for quickly testing snippets of code and debugging. But it's not a good way to develop Python programs, because the commands aren't saved anywhere.

In order to develop Python programs, we'll need to make files containing Python code. We'll then be able to use the interpreter to run them from the command line. This way, we can save all our commands, but still see what's happening.

This is a very common way to develop using Python -- use an IDE or text editor to create Python files, then run them from the command line.

In order to make a file that Python can execute on the command line, we'll need to add some lines to a blank file:

if__name__ == "__main__":

print("Welcome to a Python script")

The code above will print Welcome to a Python script when it's run from the command line. To run it, we just need to put those lines into a file, and then call it with python file.py(assuming the file is called file.py).

This works because the __name__ variable in Python scripts is automatically set to the name of the module. If the module is being run from the command line, it will be set to __main__. Checking this allows us to tell if a script is being run from the command line or not.

Instructions

Create a file called script.py in the /home/dq folder that contains the following code:

if __name__ == "__main__":    print("Welcome to a Python script")

Finally, save the file and run it using python script.py.

/home/dq$ echo -e 'if __name__=="__main__":    print("Welcome to a Python script

")'>script.py                                                                   

/home/dq$ python script.py                                                      

Welcome to a Python script