Beginner's Python

Chapter 1

First Program - Hello World!

print ("Hello World!")

Comments and Clearing Screen

# Clear the Screen
import os
os.system('cls')

# This is a comment
print ("Hello World!")

Variables

# variable names must not contain spaces
# python people tend to use underscores rather than camel case
first_name = "John"
print (first_name) # Print the string variable

Intro to Data Types

5 main ones

Strings

name = "John"
name = 'John'

Numbers

age = 0

Lists

first_name = ["John", "Bob"]

Tuples

# Tuples are immutable lists
first_name = ("John", "Bob") 

Dictionary

fav_pizza = {
    "John": "Pepperoni",
    "Bob": "Cheese",
    "Tina": "Supreme"
}
print (fav_pizza["John"]) # return the value for the key of John

Strings

talking = "My mom yelled "Clear your room"" # this will return an error
talking = 'My mom yelled "Clean your room"' # this will work
talking = "My mom yelled 'Clean your room'" # this will work
talking = "My mom yelled \"Clean your room\"" # this will work because of the escape characters
# \n is a new line character

String Manipulation

my_string = "my name is John Elder"

print (my_string.upper()) # this capitalizes all character in the string
# other string methods
# .lower() - makes every character lowercase
# .capitalize() - capitalizes first word
# .title() - capitalized everyone
# .swapcase() - swaps cases of each character
print (len(my_string)) # return number of characters in the string
print (my_string[0:7]) # return "my name"
# .split creates a list by breaking up the string based on the character you pass into it

Math with Python

print (2 + 3) # addition
print (2 - 3) # subtraction
print (2 * 3) # multiplication
print (2 / 2) # division
print (2 ** 2) # exponent
print (10 % 3) # returns the remainder, so 1 in this case

Floats and Ints

x = 3
int(x) # this forces x to be an integer
round(10/3, 4) # this returns 3.3333

Assignment Operators

# Assignment operators
num = 4 # this makes num 4
num += 1 # this adds 1 to num
num -= 2 # this substracts 1 from num
# other assignment operators: *=, /=, %=

Lists

names = ["John", "Bob", "Mary"]
# lists can be of any data types and they can be mixed
# you can have lists of lists
del names[0] # this deletes "John" from the list
names.append("Tina") # add Tina to the end of the list

Tuples

# tuples are faster to read/write at the processors level
# you can't add to tuples, but you can create new tuples from others
tuple_1 = (1, 2, 3)
tuple_2 = (4,)
tuple_3 = tuple_1 + tuple_2 # this returns (1, 2, 3, 4)

Dictionary

fav_pizza = {
    "John": "Pepperoni",
    "Bob": "Cheese",
    "Tina": "Supreme"
}
del fav_pizza["John"] # you can delete entires in a dictionary
fav_pizza["John"] = "Ham" # you can modify entries
fav_pizza.update({"Tim":"Green Peppers"}) # you can also add entries

Chapter 2

Comparison Operators

# ==, !=, >, =>, <, =<
# string comparisons are case sensitive

Conditional Statements

# IF
num = 20
if (num > 10):
    print ("Your number is greater than 10")
# ELSE IF
elif (num = 3):
    print ("Your number is 30")
# ELSE
else:
    print ("Your number is not greater than 10)

Multiple Conditional Statements

# and, or
num = 20
if (num > 10) and (num < 100):
    print ("Your number is greater than 10 and less than 100")

While Loops

counter = 0
while (counter < 10):
    print ("The count is: %s" % counter)
    counter += 1

For Loops

name = "John"
# or name = ["John", "Bob", "Mary"]
for x in name:
    print (x)

fav_pizza = {
    "John": "Pepperoni",
    "Bob": "Cheese",
    "Tina": "Supreme"
}
for key, value in fav_pizza.items():
    print(value)

FizzBuzz

counter = 0
while (counter <= 100):
    if ((counter % 3 == 0) and (counter % 5 ==0):
        print ("%s - FizzBuzz" % count)

    elif (count % 3 == 0):
        print ("%s - Fizz" % count)

    elif (count % 5 == 0):
        print ("%s - Buzz" % count)

    else:
        print (count)
    counter += 1

Chapter 3

Functions

def namer(first_name, last_name):
    print ("Hello %s" % first_name)
    print ("Hello %s" % last_name)

name("John", "Elder")

More Functions

def namer(name)
    return ("Hello %s" % name)

my_namer = namer("John")

print (my_namer)

Modules

# see the python module index for all of the built-in modules
# adding the below to a file namer_module.py
def namer(name)
    return ("Hello %s" % name)

# we can then call that function from a different script
import namer_module
print (namer_module.namer)

Intro to Classes

Everything in python is an object

# two parts defintion and instantiation

class Square:
    def __init__(self, side_length)
        self.side_length = side_length

    def area(self):
        return self.side_length * self.side_length

    def perimeter(self):
        return self.side_length * 4

    def report(self):
        print ("Side Length: %s" % self.side_length)
        print ("Area: %s" % self.area)
        print ("Perimeter: %s" % self.perimeter)

my_square = Square(10) # pass in a side length of 10
print (mySquare.side_length) # returns 10
print (mySquare.area())
mySquare.report()