Python Fundamentals

Learning Objectives

Students Will Be Able To...

• Create a variable in python
• Assign the different data structures to variables
• Write python statements using control flow
• Write python statements using loops and iteration

---

Context

• The fundamentals of programming translate throughout every language
• Like learning any new language we're going to start with the basics and build up
• If you wanted to learn English you wouldn't start by reading a novel, but with the alphabet

Variables

• Variables are a way to store and save data for use
• This is called assignment. You are assigning a value to a variable
• Declaring Variables
  • Cannot start with a number
  • Cannot declare with special characters
  • Written in snake case
• Open up Python in the terminal

name = "Jason"
fav_num = 8
turtles = ["Raph", "Leo", "Mickey", "Donny"]

Data Types

• Now you may have noticed that variables can hold different types of values
• These are called Data Types and python3 has many built-in types
  • Strings
    • Sequence of 0 or more characters(a-z, A-Z, 0-9, !,@,#, ect).
    • python type str() or with the literal '' or ""
    • methods to know
      • .format() [https://pyformat.info/](More info)
      • .isdigit(), islower(), isupper(), check to see if the string is a digit and so on. There are many more like these
      • .lower(), .upper() changed the string to lower and up case
      • .split() changes the string to a list based around the character[s] given
  • Numbers
    • Floats
      • decimals
      • python type float() or with the literal 23.3
      • methods to know
        • is_integer() Return True if the float a whole number, and False otherwise
    • Integers
      • whole number
      • python type int() or with the literal '4'
  • Lists
    • Ordered sequence of items
    • python type list() or the literal ['a', 'b', 'c']
    • methods to know
      • .append() adds a item to a list
      • .pop() removes and returns the last item from the list
  • Dictionary
    • Collections of key, value pairs
    • python type dict() or the literal {'key':'value'}
    • methods to know .get() return the value of a give key, or a default value if its not found .values() returns a list of values in the Dictionary .keys() returns a list of keys in the Dictionary
  • Booleans
    • Represents something that is True or False
    • python type 'bool()' or the literal 'True'
  • Range
    • Range is a special type that represents range of numbers
  • None
    • nothing, nothing at all
    • python type ... there inst one only the literal None

Notable built in functions

• len() return the length of the given sequence
• help() shows help documentation of the given object
• dir() show the available methods of the give object

Math Operators

All math operators can be done on both floats and ints Python comes with the following symbols for mathematical operators.

• + add
• - subtract
• * multiplication
• \ division
• \\ floor divided, always returns a whole number
• % modulo: finds the remainder after division
• The language also supports PEMDAS
  • 5+(50+5)

Comparison Operators

• == equality
• != not equal
• < less then
• <= less then or equal to

• greater then

• >= greater then or equal to

Control Flow

• Now we have reached if/else statements
• If an expression you passed in is True do something
• Else do something else

if expression == true:
    run code
    
if name == "Jason":
    print("That is an awesome name")
else: 
    print("You should get a different name")
    
if number > 100:
    print("That's a big number")
elif number > 50 && number < 100:
    print("That's a medium number")
else:
    print("Your number is puny")

• Things to note
  • Put a colon after the expression you want to evaluate
  • if to elif to else
  • indents show what code is part of the body of the statement and where it ends

Lists and Indexing

• What if you wanted to store more data.
• Can be assigned to variables
• Can hold different data types at once
• The values are indexed for us starting at zero

my_list = ["Jason", "Anna Kendrick", 2015, True]

my_list[0] == "Jason" # True

my_list[2] == 2016 # False

• Just a heads up indexing through a list is similar to indexing with strings.
• the value at index zero will be the first element in the list, or the first letter in a string

Functions and Statements

• We declare our functions with the word def for define
• Functions follow the same naming principles as declaring variables
  • Snake case
  • Do not start with numbers or special characters
• Remember how we used white space to organize our code with if/else statements. Well that idea holds true everywhere in Python

def my_name():
    return "My name is Jason"

• Functions allow us to build code that is reusable
• This follows the concept of DRY - Don't Repeat Yourself
• Functions can also take arguments. These allow our functions to be more dynamic

def my_name(name):
    return "My name is " + name

• When there is no return statement, the function implicitly returns None

for loops

for loops iterate over a sequence. There are 2 parts to a for loop, the statement and the body. The statement tells the loop what to iterate over and assigns the loop variable. The body tells python what to do in each iteration. Before each iteration the loop variable is assigned to the next value in the sequence, in oder from the zero index to the last item.

teachers = ['billy', 'tom', 'jason', 'jeff']
for teacher in teachers:
    print( teacher.capitalize() )

In this loop we iterate over each teacher in the loop and print there name capitalized.

while loops

Unlike for loops, while are not bound to a sequence and can continue for ever. like a for loop, while loops have 2 parts, an statement and a body.

num = input('Please enter a whole number: ')
while not num.isdigit():
    print('Not a whole number!')
    num = input('Please enter a whole number: ')

loop control

There are 2 ways can control what loops. They both with for and while loops in the same way.

• break The break statement stops loop and allows python to move on to the rest of the script. If you are using a while loop, you should have a break statement to stop the loop.

count = 1
while True:
    count *= count
    if count > 100: break

• continue The continue statement skips to the next iteration of the loop. Generally, continue statement are at the top of the loop body.

for num in range(100):
    if num%10 != 0: continue
    print(num)