Lesson 9 - Python Programming (Automate the Boring Stuff with Python)

Summary

Lesson 9 of 'Automate the Boring Stuff with Python' introduces Python functions, explaining how they act as mini-programs to organize code, reduce duplication, and improve readability. The lesson covers defining functions with the `def` statement, using parameters and arguments, and incorporating return values with the `return` statement. It clarifies terminology distinctions between parameters and arguments, demonstrates how functions can be part of expressions, and highlights the default `None` return value. The video also explores keyword arguments, such as `end` and `sep` in `print()`, to customize behavior. Overall, it emphasizes writing clean, maintainable, and efficient Python code.

Takeaways

• 😀 Functions are mini-programs within a program that execute code when called.
• 😀 The `def` statement is used to define a function, and the code inside the function is its body.
• 😀 Functions help eliminate code duplication, making programs shorter, easier to read, and easier to update.
• 😀 Parameters are variables defined in the function parentheses, while arguments are values passed to the function when called.
• 😀 Function calls can be part of expressions because they return values.
• 😀 The `return` statement specifies the output of a function; if omitted, the function returns `None` by default.
• 😀 The `print()` function outputs strings as a side effect and returns the special `None` value.
• 😀 Keyword arguments allow customization of optional behavior in functions, such as `end` and `sep` in `print()`.
• 😀 Using keyword arguments, you can control line endings and separators for multiple values printed by `print()`.
• 😀 Understanding parameters, arguments, return values, and keyword arguments is essential for writing clean and reusable functions in Python.

Q & A

What is a function in Python?

A function is a block of reusable code that performs a specific task. It is like a mini program within a program and executes only when it is called.

How do you define a function in Python?

A function is defined using the `def` statement followed by the function name and parentheses containing optional parameters. The code block inside is indented. Example: `def hello():`

What is the difference between parameters and arguments in a function?

Parameters are variables defined inside the parentheses of a function definition, whereas arguments are the actual values passed to the function when it is called.

Why are functions useful in programming?

Functions reduce code duplication, making programs shorter, easier to read, and easier to maintain. They allow code to be reused multiple times without rewriting it.

What does the `return` statement do in a function?

The `return` statement specifies the value that a function call evaluates to. If a function does not have a return statement, it returns `None` by default.

Can function calls be part of expressions? Give an example.

Yes, function calls can be used in expressions because they evaluate to their return value. Example: `result = 'hello has ' + str(len('hello')) + ' letters'`.

What does the `print` function return?

The `print` function returns a special value called `None`, which represents the absence of a value. It displays the output as a side effect but does not return the string.

What are keyword arguments in Python functions?

Keyword arguments are optional arguments that allow you to specify the behavior of a function call. For example, in `print()`, `end` and `sep` are keyword arguments that control the line ending and separator between values.

How do the `end` and `sep` keyword arguments modify the behavior of `print()`?

The `end` argument changes what is printed at the end of the output (default is a newline), while the `sep` argument changes what separates multiple values (default is a single space).

What happens when a function is defined but not called?

When a function is defined but not called, Python stores the function definition but does not execute its code. The code inside the function runs only when the function is called.

Explain the term 'D duplication' mentioned in the script.

'D duplication' refers to the practice of removing duplicated or copy-pasted code in a program. It makes the code shorter, easier to read, and easier to update.

What happens internally when a function is called multiple times?

Each time a function is called, execution moves to the top of the function, runs the code inside it, and then returns to the point where the function was called. This happens independently for each call.