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Key Terms

• Don't Repeat Yourself (DRY) is a principle of software engineering aimed at making it easier to maintain, update, and debug code.

• Functions are named containers for statements that can be invoked to execute code, improving readability and reducing repetition.

• Built-in functions like print(), len(), and type() come with Python, so they can be called without being defined first.

• A docstring is a string written on the first line of a function's body that describes what the function does. VS Code and the built-in help() function show it to whoever is about to call the function.

• Parameters are placeholders for inputs given to the function. Parameters can be used by their function to change the function's behavior.

• Arguments are the actual values given when invoking a function.

• Return statements allow functions to produce values that can be used elsewhere in your program and terminate function execution. A function with no return statement returns None.

• Parameters can have default values, and arguments can be passed by keyword as well as by position.

• A NameError is raised when a line uses a name that does not exist at the moment that line runs: the name is misspelled, it belongs to a different function's scope, or it is assigned (or its function is defined) further down the file than the line that uses it.

• A TypeError is raised when a value is the wrong type for what the code asks of it, such as adding a string to a number, or when a function is called with the wrong number of arguments.

• Scope determines where variables can be accessed.

  • Global scope is the file, outside of any function. A variable assigned there is reachable anywhere in that file.

  • Local scope is the inside of a function. A variable or parameter assigned there exists only while that function is running and is reachable only within it.