The Terminal and Program Arguments

Introducing the Terminal 💻

• pwd
• ls
• cd
• Running python scripts
  • python hello_world.py

Program Arguments

Some programs take arguments

• cd directory
• python script.py

Can we write a python script that takes arguments?

🤔

arg_demo.py

Program arguments are usually separated by spaces.

If you want to include a space in your argument, surround your argument with single quotes.

python arg_demo.py separate arguments

vs

python arg_demo.py 'single argument'

The terminal uses many special symbols for different purposes.

For example, { } ( ) < > | & * $ @ ! ~ all have a special functions.

If you want to include a symbol in a program argument, it's a good idea to wrap it in single quotes.

python arg_demo.py * 7

vs

python arg_demo.py '*' 7

What is sys.argv?

A list!

What if I just want the "first" argument? How would I get it...?

🤔

Indexing

hello.py

You can access a specific item in a list (or string or tuple!) using the indexing operator [...].

• First item is at [0]
• Second item is at [1]
• Etc.

Remember that the first item in sys.argv (i.e. sys.argv[0]) is the name of your script!

What happens when you have more commandline arguments than the program uses?

python hello.py John Susan

The extra arguments are ignored.

What happens when you don't supply as many arguments as the program uses?

python hello.py

You will get an IndexError when python tries to grab a value from a list position that doesn't exist.

repeat.py

The contents of sys.argv are strings.

Change them to other types as needed.

👨🏼‍🎨 things.py

Write a program that prompts the user to input things. After they are done, print the list of things.

The number of things to input and the prompt text should be specified on the commandline.

$ python things.py 3 'Fruit or veggy'
Fruit or veggy: apple
Fruit or veggy: pear
Fruit or veggy: broccoli

- apple
- pear
- broccoli

$ python things.py 5 Major 
Major: Bioinformatics
Major: Mathematics
Major: Linguistics
Major: Vocal Performance
Major: History

- Bioinformatics
- Mathematics
- Linguistics
- Vocal Performance
- History

Key Ideas

• The terminal!
• Program arguments, sys.argv
• Indexing into a list, [0], [1], etc.