Lecture 4, Thu 01/18

Math / Random Modules, Function Basics

Recorded Lecture: 1_18_24

Math and Random Modules

• Python contains certain modules that can be useful in our programs, such as math and random
  • These modules will need to be imported in our code in order to use them
  • Python already allows us to use certain things like print() and input() without needing to import anything since this functionality is common
  • But certain functionality (like math functionality) may only be needed in certain programs
  • Instead of having Python load ALL modules it can provide, it requires programmers to explicitly import them for performance reasons
• Examples of some math functionality in the math module:

import math

print(math.ceil(3.1)) # 4
print(math.floor(3.9))# 3
print(math.factorial(4)) # 4*3*2*1 -> 24
print(math.pow(4, 2)) # 4 ** 2 -> 16
print(math.pi) # 3.141592653589793
print(math.sqrt(81)) # 9.0

• Examples of some functionality in the random module

import random
print(random.random()) # [0, 1)
print(random.randrange(2, 8)) # [2, 8)

print(random.randint(2, 4)) # [2, 4]
print(random.randrange(2, 5)) # same as random.randint(2,4)

• Example of simulating a six-sided die roll and a pair of dice:

import random

# Rolling one six-sided die
print(random.randrange(1, 7)) 

# Rolling two six-sided dice
print(random.randrange(1, 7) + random.randrange(1, 7))

Introduction to Functions

• We’ve seen how we can call functions that Python provides (print(), input(), type(), …)
• Functions are great when:
  • We have common code that is used in various places in our code
  • Instead of copy / pasting the same code in various places, we can write a single function to be used and called in various places in our code
    • Can you imagine how our code would look if we had to copy / paste code that makes the print() function work in every place we use it!
• Let’s write a simple function definition, something that takes in an integer and doubles it:

def double(n):
	''' Returns 2 times the parameter''' # Good to comment functions!
	print("In double function. n =", n)
	print(2 * n)

• The def keyword let’s Python know we are about to define a function
• double is name (identifier) of the function
• The (n) denotes the parameter(s) that this function will accept. In this case, it takes in a single value and is used in the function
  • Note that a function may have zero or more parameters
• The : is necessary to tell Python we’re about to define the body of the function (statements belonging to the function)
• The parameter(s) of a function is referred to as a function signature
• The actual statements in the function are called the body of the function
• All statements in the function body need to be indented (single tab) so python can associate these instructions as part of the function definition
• A function may or may not have a return statement
  • If a return statement returning an actual value exists, then the value is returned to the caller and can be used
  • If no return statement exists (or a return statement exists, but doesn’t return an actual value), then a special None value is returned
  • Depending on the situation, a function may or may not want to have an explicit value returned
  • For example, if a function should print something, then it just needs to print something and exit the function (without passing any data back to the caller of the function)
    • Note that print() does not have a return value
  • But if the function needs to compute a value and return this computation back to the caller (like our double function example), then an explicit return statement is needed
• Example of having a return statement:

def double(n):
	'''Returns 2 times the parameter''' # Good to comment functions!
	print("In double function. n =", n)
	return 2 * n

• Examples of how we can call functions (see if you can trace the flow of function calls and how return values are used):

print(double(10)) # -> print(20)
print(double(double(2)) # -> print(double(4)) -> print(8)
value = double(5) + double(6) # -> 10 + double(6) -> 10 + 12 -> 22
print(value)