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

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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 add(name):
    return "My name is " + name

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