Creating Functions: def and Parameters

We have already used ready-made functions such as print(), len() and input(). A function is a named piece of code that is called when needed. Instead of repeating the same code in several places, we move it into a function and call it by name, which makes the program shorter and errors easier to find.

A function is declared with the keyword def: after the line def hello(): the body is written indented by 4 spaces, for example print("Salom!"). Declaring a function does not run it; it executes only when we call it: hello(). The call must come after the declaration.

Data is passed to a function through parameters: def greet(name): and print("Salom,", name). The value given in the call is called an argument: greet("Dilnoza"). Several parameters are separated by commas: def area(a, b):. A parameter may have a default value: with def greet(name="do‘st"): the call greet() prints “Salom, do‘st”.

Variables created inside a function are local: they are visible only within that function and disappear when it ends. Global variables created outside a function can be read inside. Give functions meaningful names (print_table, area) and let each one do one clear job.

Key takeaways

• A function is declared with def and called by its name.
• A parameter is the name in the declaration; an argument is the value in the call.
• A parameter can have a default value.
• Variables inside a function are local.