Module 1 - Tutorial - Basic Python

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Setting values to variables

The value types that we will be using in this course are mainly int, float, and string values.

• An int value is an integer (whole numbers)

• A float value is a decimal number

• A string value is alpha-numeric characters that cannot be mathematically computed; can use single or double quotes

• The pound/hashtag (#) sign denotes comments, which is not read by python as code

x = 5 #int

y = 7.23 #float

z = 'hello world' #string

#use the "print" function to see the output of the values stored in the variables

print(x)

print(y)

print(z)

#Jupyter notebooks can display the output of a variable's value by typing the variable name but only will output the last "called on" variable

y #this will not display

z #this will display b/c it's the last

#the "type" function will tell you what data type a variable is

type(z)

#variables can be added together

a = x + y

print(a)

#also works for strings

r = "hello"

s = "world"

print(r + s)

If Statement

• Checks if a condition is true

• Python will auto-indent starting from the first line after the colon within the If statement

• Indentation signifies the code that belongs to the If statement

• Note: != is "not equal to"

#check to see if something is true

#can also use other tests of equality >, <, !=

if x == 5: 

    print("It is five.")

else:

    print("It is not five.")

Lists and For loops

• A list is a container for multiple values

• A For loop goes through each item within a list and executes the code that should be done for each item

• Python will auto-indent starting from the first line after the colon within the loop

#this is a list with 3 items

colors = ['red', 'yellow', 'blue']

#iterating through a list

for color in colors:

    print(color)

• The len function returns the length (number of) items

print(len(colors))

print(len(z)) #also works on counting characters (including spaces and punctuation) in a string

• Python position counting (called "index") starts from 0

• To "slice" a list is to look at particular specified values

• The first number is the starting index of the value to get and the 2nd number after the colon is the index to stop at (not inclusive)

#this list has 7 items

#position index starts at 0 and ends at 6

days = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday']

days[2:6] #2nd number is up to but not including that index number

Dictionaries

• Similar to lists, dictionaries are a container type to store values

• Items in dictionaries are stored with a key:value pair (like a physical dictionary - you look up a word (key) and find the definition (value))

• Instead of getting values by their positions, values are called by their key name

#dictionaries use curly brackets

pets = {'Goku': 'dog',

        'Mika': 'dog',

        'Brunson': 'cat',

        'Lucas': 'cat',

        'Genki': 'fish'}

#to see what kind of pet Mika is, look up the key "Mika" for the dictionary "pets"

print(pets['Mika'])

#see the entire dictionary

print(pets)

#list of keys

pets.keys()

#list of values

pets.values()

#add new values to a dictionary

#type the dictionary name with the new key in square brackets

#then set equal to the value for the key

pets['Tiny'] = 'dog'

print(pets)

#iterating over a dictionary

#items functions gets key,value pair in dictionary

for name, animal in pets.items(): 

    print(name + " is a " + animal)

The def keyword

• def is used to write code to create your own function (we call this code the "function definition")

• Python will auto-indent starting from the first line after the colon (this is called the "function body")

• The blue letters are the name of your function (no spaces are allowed in function names)

• Inside the parentheses go the placeholder variables for the arguments (what will be passed into the function to compute on)

• The return statement sends back a value after the function is finished (there are cases where some functions do not have a return statement too)

• A function definition itself does not produce any output - instead, it stores the function in-memory; the function must be called separately to "activate"

# example of making a function definition

def addNum(num1, num2):

    return num1 + num2

# example of using (or "calling") the above function

addNum(x, y)

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Appendix