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Python Unit 1
1.1 – 1.3
1 . 1 : O P E R AT O R S , E X P R E S S I O N S , A N D
VA R I A B L E S
1.2: STRINGS, FUNCTIONS, CASE
S E N S I T I V I T Y, E T C .
1 . 3 : O U R F I R S T T E X T- B A S E D G A M E
Python – Section 1
Text Book for Python Module
 Invent Your Own Computer Games With Python
 By Al Swiegert
 Easily found on the Internet:
 http://inventwithpython.com/chapters/
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Hint For Slides in This Class
 Code is typically in Courier New font.

For Example:
print(‘Hello Everybody’)
 This is a common font to represent computer
code within textbooks.
 You can access the slides on the Intranet.
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OPERATORS,
EXPRESSIONS, AND
VARIABLES
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Objectives
 By the end of this unit, you will be able to:
 Work in IDLE
 Define an Interpreter and describe its role Python
 Define Integers and Floating Point Numbers
 Work with Operators and Expressions
 Work with Values
 Store Values in Variables
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Python Interpreter and IDLE
 Interpreter – A program that processes each statement in a
program. Three step process:
1.
2.
3.
Evaluate (Does this statement look valid)
Translate (Convert from Python to machine code)
Execute (Make the machine perform this statement)
 IDLE – Integrated Development Environment
 Text editor for writing and testing Python programs.
 Cross-platform (Unix, Linux and PC)
 Ships with all versions of Python
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IDLE – Development Environment
• IDLE helps you program in Python by:
– color-coding your program code
– debugging
– auto-indent
• The example above demonstrates the “Python Shell”.
• >>> Python Command Goes Here
• The Python Shell executes your command when you press enter.
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Hello World – In IDLE (Students Follow Along)
>>> print('hello world')
hello world
>>>
 Enter your command to the right of the >>> symbols:
>>> print('hello world')
 The Python Interpreter prints the result of the command
on a line without the greater than signs:
hello world
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Operators and Expressions
 Operators and Operations

Basic Operators:
+ - / *
 Expressions

Calculations performed by
combining values and
operators.
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Math in IDLE
 Practice doing mathematical expressions in IDLE
 Do some math (guided practice)
Demonstrate a few basic math calculations
 <Alt><P> to bring up previous commands


Students practice entering mathematical expressions in IDLE
Addition
 Subtraction
 Division
 Multiplication
 Combinations of the above

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Order of precedence

Precedence - The order in which operations are
computed

Order of Precedence:
1.
Items surrounded by parenthesis (5 / 4)
2.
Exponentiation 5**4
3.
Multiplication 5*4
4.
Division 5/4
5.
Addition 5+4
6.
Subtraction 5-4
There are significantly more rules of precedence
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Language Syntax
 Syntax – the structure of a program and the rules about
that structure.
The commands and the way they are formatted in a program.
 Other special characters like {} [] () ; \
 Human readable
 Python Interpreter converts into machine code upon execution

 Syntax Error – Python doesn’t understand your command.

Demonstrate a syntax error.
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Variables
 Variable – Temporary storage for a value.
birthYear = 1964

Upon execution, the Python Interpreter creates the variable
named birthYear and assigns it the value 1964.
 Variable values are set from right to left
 You can modify the value of birthYear by assigning a
new value to it.
birthYear = 1940
#Chuck Norris’ birth
#
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year.
Variables in Other Languages
 In most other languages you must explicitly create the
variable named birthYear. Java Example:
int birthYear;
birthYear = 1964;
 Data Type - The int identifies the type of data that
may be placed into the birthYear variable.
 Python does this for you based upon the type of value
assigned to the variable.
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Data Types
 Data Type – The way variables are stored and utilized
within the computer. Types:
 Integer (Whole number) -
myAge = 47
 Float (Decimal) - myWeight
 String - myName
= ‘Mr. Teacher’
 Boolean - isTeacher
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= 221.34
= True
Demonstration of variables (in IDLE)
>>> age = 47
>>> Age
Returns the value 47
>>> age + 5
Returns the value 52
>>> age = age + 10
>>> Age
Returns: 57
>>> teacherName = 'Mr. Sweigart'
Creates a string variable named teacherName and sets its
value to: Mr. Sweigart
>>> teacherName Returns: 'Mr. Sweigart'
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Variable Demo (Continued)
>>> goodTextbook = True
 Creates a Boolean variable named goodTextbook and sets it to: True
>>> weight = 175.09

Creates a float (decimal) variable named weight and sets it to: 175.09
>>> weight = 167.5
 Changes the value of weight to: 167.5 (Returns: 167.5)
>>> newWeight = Weight + 22
 Creates a variable named newWeight and sets its value to 167.5 + 22
>>> newWeight + 22
>>> newWeight

Returns: 189.5
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String (in IDLE)
teacherName = 'Mr. Sweigart‘
teacherName = 'Mr. Johnson‘
teacherName2 = 'Mr. Newbee‘
teacher3 = teacherName + teacherName2
 What is the value of teacher3?
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Boolean (in IDLE)
>>> goodTextbook = True
•
Creates a Boolean variable named
goodTextbook and sets it to: True
>>> goodTextBook
•
Returns: True
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Float (in IDLE)
weight = 175.09
 Creates a float (decimal) variable named weight and
sets it to: 175.09
weight = 167.5
weight
Returns: 167.5
newWeight = Weight + 22
newWeight
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Returns: 189.5
Reading / Exercise(s)
 Read CH 2 (The Interactive Shell) in the Invent Your Own
Games with Python book (PDF).
 Complete the Python exercises identified on planbook:

Link goes here
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Python – 1.2
STRINGS, FUNCTIONS,
AND CASE SENSITIVITY
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Objectives
 By the end of this unit you will be able to:
 Work with data types (such as strings or integers)
 Use IDLE to write source code.
 Use the print() and input() functions.
 Create comments in your programs
 Demonstrate the importance Case-sensitivity in Python
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Working with Strings (Text)
className = ‘Video Game Programming’
o

The single quotes (apostrophes) define this as a text string.
 Try it in IDLE
String Concatenation
className = className + ‘ - and Animation’

Demonstrate in IDLE and display result.
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Hello World
 Create the hello_world.py program in IDLE
o Hello World Program - Typically the first program written when
learning a new language.
o Execute and describe the program
o Assist students in creating their own hello world
program.
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Hello World
 In Python:
print(‘Hello World!’)
 In Java:
public class HelloWorld{
public static void main (String[] args){
System.out.println("Hello, world!");
}
}
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Literals VS Variables
 Placing the literal 'Hello World' in myVariable
myVariable = 'Hello World'
 Print using a literal string (has quotes)
print('Hello World')
 Print using the value within a variable (no quotes)
print(myVariable)
 Strings inside variables are easily reused / manipulated.
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Comments
 Only for programmers to read
 Used to describe what the code does (very useful for complex code)
 You will lose points on your program if you don’t have
comments
o
Your comments need to be unique to your program
 Single Line Comments (#)
 # Comments are not recognized by the interpreter.
 Multi-Line Comments (''')
'''
Multiple lines of comments can go in the middle
'''
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Function
 Function – A mini program that you can call to do
something. Examples Include:

print() Displays a message in the Interpreter.
input() Allows a user to enter data.

Both functions are used in the hello_world.py program.

 Calling a function and executing a function are
synonymous.
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The print() Function
 Displays a message to the user.
print ('My name is Peter J. Newbee.')
 The following message is displayed
My name is Peter J. Newbee.
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The input() Function
 Most basic form of input() function:
print ('Please enter your name')
playerName = input()
print(playerName)
 A more compact form of the input() function:
playerName = input('Please enter your name')
print(playerName)
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Advanced Hello World
# This program says hello and asks for my name.
print('Hello world!')
print('What is your name?')
myName = input()
print(‘Good to meet you, ' + myName)
 Question: Is myName a good name for this variable
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Advanced Hello World
print (‘Hello World’)

Displays Hello World on the screen when executed.
print (‘what is your name?’)

Displays “What is your name?” when executed.
myName = input ()

Places the user’s response into a variable named myName.
print(‘It is good to meet you, ’ + myName)

Displays It is good to meet you, and the name entered by the user.
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Concatenation
 Concatenation – merging two or more strings together.
print(‘It is good to meet you, ’ + myName)
 Displays It is good to meet you, xxx where xxx is the
value entered when the user entered their name.

The plus sign merges the string ‘It is good to meet you,
‘ with the value of the myName variable.
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Case-Sensitivity
 Case – Capitalization or lack of capitalization of a letter.
 Case-Sensitive - Declaring different capitalizations of a
name to mean different things.
 Python is a case-sensitive language
 score, Score, and SCORE are three different variables.
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Case Sensitivity
 Variable names must be referenced in the exact case as
when created

For example:
myName = ‘Pete’
 Cannot
be referenced like this:
print(myname)
 The
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‘N’ in myName must be capitalized.
Syntax Rules for Naming Variables
 Variable names in Python:
o Can contain letters, numbers, or underscores
o Must begin with a letter or underscore.
 Functions names follow the same rules.
 The next slide discusses classroom coding standards.
o
Differences between Syntax Rules and Coding Standards???
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Standards for Variable Names
 Why are standards important?
 Our standards for naming variables:
o
o
Start with a lowercase letter
Capitalize every word after the first (Camel case).

Example:

o
userFirstName
The F and N must be capitalized to meet our standards.
Must conform to the Python syntax rules
 See previous slide for syntax rules
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Conventions for Working with Strings
 Use apostrophes (single quotes) for string
values:
•
Our Standard (single quotes)

o
print(‘Hello World’)
Not our Standard (double quotes)

print(“Hello World”)
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1.2 Reading / Exercise
 See Intranet for reading and exercises.
 Exercises 1-2-1 through 1-2-3
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Python – 1.3
OUR FIRST TEXT
BASED GAME
Python – Unit 1
Objectives
 In this unit, we will discuss the following:
o Modules and Import statements
o Arguments
o while statements
o Blocks
o Comparison Operators
o Difference between = and ==
o if statements and conditions
o The break keyword
o The str() and int() functions
o The random.randint() function
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Modules and the Import Statement
 Module – A Python program that contains useful
functions.
 import statement – Imports functions from another
module so they can be used.
import random

Makes the functions in the random.py module available within our
current module.
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The randint() function
import random
randomNumber = random.randint(1, 100)
 The above statement generates a random number
between 1 and 100 and places the number in the
randomNumber variable.
 The randint function resides in the random module,
which is copied in by the import statement.
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Arguments and Functions

Function arguments are passed inside the parenthesis of the function
call:
print(‘Hello World’)

The argument is ‘Hello World’
yourName = input(‘Please enter your name’)

Asks the user to enter their name and places the result in the yourName
variable. The argument is the text between the apostrophes.
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Arguments and Functions

Functions require that you enter the correct number of arguments:
randomNumber = random.randint(1)
o
Generates a syntax error because the randint function requires two
arguments.
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Loops
Loop – Programming logic that is executed over and
over again until a specific condition(s) is met.
Two types of loops:


while boolean_expression:
 Executes as long as the expression evaluates
to True
for
 Executes a set number of times


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Extremely useful
Covered later in course
while Loop
while boolean_expression (evaluates to
true):
# Perform block action
# Perform block action
…
while guessesTaken < 6:
# Ask the user to guess again
# Accept user’s guess
# Evaluate the guess
# Increment guessesTaken variable by 1.
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Blocks
Block - one or more lines of code grouped together with the
same minimum amount of indentation.
while guessesTaken < 6:
Execute block
o
The colon after the 6 indicates that a block will follow.
o Indented by four spaces (all lines of the block).
o The block ends when return to previous indentation.
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Block Example (while loop)
while guessesTaken < 6:
----print('Take a guess.')
----guess = input()
----guess = int(guess)
----guessesTaken = guessesTaken + 1
----if guess < number:
--------print('Your guess is too low.')
----if guess > number:
--------print('Your guess is too high.')
if guess == number:
----guessesTaken = str(guessesTaken)
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Conditions (Boolean Expressions)
 Conditions – Expressions that evaluate to
True or False (Boolean Expressions)
myAge = 50
if myAge > 49:
print (‘You are old’)
 myAge > 49 evaluates to True (the message prints)
 The following use Conditions:



if statements
while Loops
for Loops
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Comparison Operators (Conditions Continued)
while guessesTaken < 6:
Execute block
 The
< sign is the comparison operator
 When guessesTaken becomes 6, the while loop ends
and the block of code is no longer executed.
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== Versus = (Conditions Continued)
 Use = to assign a value to a variable
a = b
 Use == in a conditional (while, if , or for)
if a == b:
print (‘a has the same value as b’)
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if Statements
if guess < randomNumber:
print('Your guess is too low')
 If the user guessed a number less than randomNumber
“Your guess is too low” is displayed.
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The if Statement (Equals and Not)
if name = = 'Pete Newbee':
print('Pete is the name')
if name != 'Chuck Norris':
print('Sorry, I am not your hero')
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Compound Conditionals
Using And
if a < b and a < c:
print ("a is less than b and c")
Using Or
if a < b or a < c:
print ("a is less than either b or c")
This will not work!
if a < b or < c:
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else and elif
 Decision logic where the variable x is an integer.
if x <= 10:
print('X is less than 11')
elif x <= 20:
print ('X is between 11 and 20')
else:
print('X is greater than 20')
 elif (like saying “otherwise if”)
 else: (Default action if the if/elif conditions do
not evaluate to True)
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if Versus while
If rupees < 50:
If
keyword
while
while
keyword
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condition (Boolean Expression)
rupees > 50:
condition (Boolean Expression)
Booleans and Conditionals
isInjured = True
if isInjured:
print(‘The dragon is injured’)
True
 The following values evaluate to False:
 Any non-zero value evaluates to


The number 0
Empty strings
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(In a numeric data type)
(Example: myString = '')
The int() Function
guess = input(‘Take a guess‘)
guess = int(guess)
 Converts the text from guess into an integer value for
evaluation purposes.
Note: The getInt() function of the game_dev module
does the same as the two commands above.
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Nested Functions
 The following code converts the string that is returned
from the input function into an integer value.
 age =
int(input(‘Enter
your age?‘)
)
 The input() function receives the age and passes it
to the int() function which converts the value into an
integer.
 What would happen if the user entered a non-integer
value?
Note: Same as game_dev.getInt() function
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Incrementing Variables
 Common to most languages:
guessesTaken = guessesTaken + 1
 Increments guessesTaken by one.
 Python Shortcut:
guessesTaken += 1
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The break Statement

break – a statement that tells the program to immediately
jump out of the while-block to the first line after the end of the
while-block.
while True:
# Code to generate number would go here.
# Code to retrieve guess would go here.
if guess == number:
break
 Breaks out of the while loop if the values of the guess and
number variables are equal.
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Reading / Exercises
 See Intranet
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Unit Exam
 You will be required to write sample code for the exam.
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