Builtin Functions

The Many Functions

Python has many, many built-in functions. You could never learn them all in this course. You will learn a few, but it’s far more important that you learn how to learn more about functions.

A list of dozens of built-in Python functions are shown, including: abs, bool, zip, and sorted among many others.

Learning about a Function

Good programmers create documentation for their functions. Documentation is extra information about a function that makes it clear how it works. There are many ways to write documentation, but they usually have a few things in common.

Name: len
Description: The function "len" returns the number of characters in a string (its length).
Syntax:
	len(a_string)
Parameters:
	a_string (String): The string to calculate the length of
Returns: Integer
Example:
    len("Hello World")

Function Documentation

You should look for six major parts. The function’s name, its parameters, its return value, its description, and examples how to use the function.

The same text from the previous slide with the following words circled: Name, Parameters, Return value, Description, Examples.

Parameters and Arguments

The Arguments that are passed into a function are also known as Parameters. Parameters are the formal names that allow us to refer to a the function. In the example below, the arguments are 3, 10, and “Hello”. The documentation tells us that the corresponding parameters are X, Y, and Z.

A function call is shown:

calculate_area(3, 10)

With the following documentation below it:

Name: calculate_area
Syntax:
    calculate_area(length, width)
Parameters:
    length (Integer): The length of the rectangle
    width (integer): The width of the rectangle

Annotations indicate that the 3 and 10 are arguments, while length and width are parameters.

Nesting Function Calls

A common task is to nest function calls inside of other function calls.

print(len("Hello World"))

Arrows point from the value "Hello World" to the function name len, and then arrows point from len to the function name print.

Chaining Methods

When you need to call methods on the same string variable or value, it’s a little different. As shown below, you will repeat the period, name, and parenthese each time. By placing them side-by-side, you will keep using the same variable, modifying it in turn from left to right.

"hello world".title().count('o')

Arrows point from the value “hello world” to the method name title, and then arrows point from title to the method name count.

Functions, Methods, and Operators

Since calls are just another expression, you can freely combine them with each other. Observe the code show, where we combine string addition, a string method call, and a function. Notice the order of execution, this can be tricky to follow!

string_length = len("hello " + " world ".strip())

The string_length = is labelled as an assignment statement
The len( part is labelled as a function call.
The + part is labelled as a string addition.
The .strip() is labelled as a method call.

Input/Output

You already know two functions: Print is a function that takes in arguments and writes to the console. Input is a function reads from the console and returns it as a string value.

These two functions are strange, because they have side effects. The Input function puts a textbox on the console, and the print function writes text to the console.

On the left, the code print() On the right, the code input()