REST APIs with Flask and Python - Mutable Default Parameters (and Why They're a Bad Idea)

The video tutorial discusses the pitfalls of using mutable default parameters in Python functions. It uses a student class example to illustrate how mutable defaults can lead to unexpected behavior, such as shared state between instances. The tutorial explains that default parameters are evaluated when the function is defined, not when called, leading to shared mutable objects. To avoid this, it suggests using None as a default and initializing the mutable object inside the function. The video concludes with advice to use immutable defaults like integers or strings to prevent such issues.

What is a potential issue when using a list as a default parameter in Python?

• The list will cause a syntax error.

• The list will automatically convert to a tuple.

• The list will be shared across all instances using the default.

• The list will be empty for every function call.

Why do mutable default parameters cause unexpected behavior in Python?

• Because they are evaluated every time the function is called.

• Because they are evaluated when the function is defined.

• Because they are not allowed in Python.

• Because they automatically become immutable.

How can you avoid the issue of shared mutable default parameters?

• By using a mutable object as a default parameter.

• By using a different programming language.

• By initializing the mutable object inside the function.

• By using a global variable instead.

What is a recommended practice for default parameter values in Python?

• Use immutable objects like integers and strings.

• Use mutable objects like lists and dictionaries.

• Avoid using default parameters altogether.

• Use global variables as default parameters.

What type hint can be used to indicate an optional list parameter?

• List[int]

• Any[List[int]]

• Union[List[int], None]

• Optional[List[int]]