Python Basics

Printing

• Output any expression to the screen using the print() function.
• To print a blank line use the following code: print()

print("Hello World") # Hello World
print("The answer of 2+2 is: ", 2+2) # The answer of 2+2 is: 4
print("The answer of 2+2 is: ", "2+2") # The answer is: 2+2

• To output double quotes within the text, use ". This is called an escape code.

print("Hello \" World ") # Hello " World

• Some other important escape codes are listed in the table below.

Escape Code	Description
'	Single Quote
"	Double Quote
\t	Tab
\r	Carriage Return
\n	Linefeed/New Line

• If we wanted the code output to print on the same line, it can be done by using a new option to set the end character. The example below prints: PinkOctopus

print("Pink", end="")
print("Octopus")

• We can also use a space with the end character. The example below prints: Pink Octopus

print("Pink", end=" ")
print("Octopus")

Comments

• Comments can be added by using the # symbol at the beginning of a line.
• A codeblock can also be commented by adding ‘’’ three single quotes.

print("Hi")
'''
This is
a
multi
line
comment. Nothing
Will run in between these quotes.
print("There")
'''
print("Done")

Assignment Operators

• Same basic rule as other languages: the right hand side is assigned to the left hand side.
• There are assignment operations for addition, subtraction, multiplication and division.

# Create a variable x
# Store the value 10 into it.
x = 10

# This prints the value stored in x.
print(x)

# This prints the letter x, but not the value in x
print("x")

# This prints "x= 10"
print("x=", 10)

Variables

• Variables should start with a lower case letter.
• Variables can start with an upper case letter or an underscore, but those are special cases and should not be done on a normal basis.
• Variables are case sensitive as in the example below. X and x are two different variables.

x = 6
X = 5
print(x)

• The official style guide for Python says that multi-word variable names in Python should be separated by underscores. But do I care? Both my_variable and myVariable works.
• Constant variables can have an upper-case name e.g. MAX_SPEED, MAX_SCORE, etc.

Operators

• Some operators are listed in the table below for reminders.
• The official style guide for Python says that there should be a space before and after each operator.

Operator	Operation	Example Equation	Example Code	Output
+	addition	3+2	a = 3 + 2	5
-	subtraction	3-2	a = 3 - 2	1
*	multiplication	3x2	a = 3 * 2	6
/	division	10/2	a = 10 / 2	5
//	floor division	N/A	a = 10 // 3	3
**	power	2^3	a = 2 ** 3	8
%	modulus	N/A	a = 8 % 3	2

Trigonometric Functions

• Math library is available for trigonometric functions: math. Example to import everything from math is given below.
• Units are in radians.

# Import the math library
# This line is done only once, and at the very top
# of the program.
from math import *

(10)
x = sin(0) + cos(0)

Input

• Input in Python is text only; need to be converted to other data types.

number = input("Enter your number: ")
number = float(number)

# Can be done in one step
number2 = float(input("Enter your second number: "))

If Statements

• The if statement allows a computer to make a decision.
• Indentation matters a lot here. If blocks use indentation to know whether to execute or not.
• An if statement can check multiple conditions by chaining together comparisons with and and or.

# Variables used in the example if statements
a = 4
b = 5

# Basic comparisons
if a < b:
    print("a is less than b")

if a > b:
    print("a is greater than b")

print("Done")

# Indentation must be the same, this does NOT work
if a == 1:
  print("Indented two spaces.")
    print("Indented four. This will generate an error.")
   print("The computer will want you to make up your mind.")

Conditional Operator	Description
<	Less Than
>	Greater Than
<=	Lesser Than or Equal
>=	Greater Than or Equal
==	Equal
!=	Not Equal
and	AND Operator
or	OR Operator
not	NOT Operator

Boolean Variables

• Boolean variables are: True and False.

# Boolean data type. This is legal!
a = True
if a:
    print("a is true")

• The not operator flips the value. So if a is true, you can make it false by using ‘not a’.

# Using not
a = True
b = not a # Value in b is 'False'

# How to use the not function
if not(a):
    print("a is false")

# Can also be used like this, looks better - use this
if not a:
    print("a is false")    

• You can compare and assign at the same time. Check the code block below.

a = 3
b = 3
# This next line is strange-looking, but allowed.
# c will be true or false, depending if
# a and b are equal.
c = a == b
# Prints value of c, in this case True
print(c)

• If you do ‘if 0’, then it is treated as false. It won’t run. Any value other than 0 will be true.

# Nothing will be printed
if 0:
    print("Zero")

# Will print
if 1:
    print("1")
if "A":
    print("A")

• Another weird example is given below. b is always true in the first if statement so it’ll print no matter what.

a = "c"
if a == "B" or "b":
    print("a is equal to b. Maybe.")

# This is the way to do the if statement for comparison with a
if a == "B" or a == "b":
    print("a is equal to b.")

Else and Else If

• Else is just else:
• Else If is elif **:
• REMINDER: Order of execution matters.

temperature = int(input("What is the temperature in Fahrenheit? "))
if temperature > 90:
    print("It is hot outside")
elif temperature < 30:
    print("It is cold outside")
else:
    print("It is not hot outside")
print("Done")

Text Comparisons

• It is possible to use an if statement to check text.

user_name = input("What is your name? ")
if user_name == "Zain":
    print("You have a nice name.")
else:
    print("Your name is ok.")

• If the program needs to match regardless as to the case of the text entered, the easiest way to do that is to convert everything to lower case. This can be done with the lower command.

user_name = input("What is your name? ")
if user_name.lower() == "zain":
    print("You have a nice name.")
else:
    print("Your name is ok.")