07 - Using Functions.md

Using Functions

Functions are isolated pieces of code that take input, perform some operation, and return a result. Functions we've used so far include input(), print(), len(), etc. Python provides many built-in functions for you to use. For all the built-in functions, check the official docs

• I/O
  • input() prompts the user for input on the terminal
  • print() displays text to the user on the terminal
• Arithmetic Functions
  • abs() returns the absolute value of a number
  • round() rounds a number, an optional second argument can specify how many decimal places the output should have
  • min() returns the minimum of the values passed to it
  • max() returns the maximum of the values passed to it
  • sum() returns the sum of the values passed to it
• Type Conversion
  • int() converts a value to an int
  • float() converts a value to a float
  • str() converts a value to a string
  • chr() converts an int to a string containing the character with that unicode value, for example chr(97) returns the string 'a'
  • bool() converts a value to a boolean
  • list() converts a value to a list
  • tuple() converts a value to a tuple
  • set() converts a value to a set
  • dict() converts a value to a dict
• List Operations
  • len() returns the length of a list
  • sorted() sorts a list
  • reversed() reverses a list

Parameters and Return-Values

Parameters are the values passed to a function, enclosed inside the parantheses. Some functions take no parameters, some like min and print take an arbitrary number of parameters. Functions may also take named parameters. For example, the print function can take a named parameter end. When not specified, end will default to \n. This is useful if you want to print multiple things on the same line.

print('hello ', end='')
print('there')
>>> hello there

Functions may or may not return anything. If they don't return anything, any variables they're assigned to will be None.

x = print('hello!')
print(x)
>>> None

By default if you put multiple arguments into a print statement they will print with a space between them:

print('hey', 'there')
>>> hey there

This can be changed by adding the separator argument sep.

print('hey', 'there', sep='-')
>>>hey-there

Returning Something or Nothing

Generally, if they do not return anything, they'll edit the object that they're called on, or the parameters they're passed, or do something else entirely. For example, the print function doesn't return anything. Any variable to the result of print will be None

x = print('hello!')
print(x) # None

Another example is list.append().

fruits = ['apple', 'banana', 'pear']
x = fruits.append('cherry')
print(x) # None
print(fruits) # ['apple', 'banana', 'pear', 'cherry']

Functions on classes are called methods. Methods are a special type of function: all methods are functions, not all functions are methods. Some examples of methods include list.append() and string.split(). Note that you also have a . before a function if it's contained in a module. For example random.randint() and math.sin(), however these are not methods.