Title: Guide to Programming with Python
1Guide to Programming with Python
- Chapter One
- Getting Started The Game Over Program
2Objectives
- Introduce Python
- Demonstrate how to install Python
- Explain how to print text to the screen
- Describe comments and how to use them
- Demonstrate Pythons development environment,
IDLE, using it to write, edit, run, and save
programs
3Examining the Game Over Program
- Figure 1.1 Game Over Program Output
- The all-too familiar words from a computer game
4Examining the Game Over Program (continued)
- Hello World program By tradition, prints
"Hello, world! - Often used as first program
- Console window Provides a text-based interface
to Windows operating system - Terminal application Provides a text-based
interface to Mac OS X and Linux operating systems
5Introducing Python
- Powerful yet easy to use programming language
- Developed by Guido van Rossum
- First released in 1991
- Named after comedy troupe Monty Python
- An alarming number of references to spam, eggs,
and the number 42 in documentation
6Python Is Easy to Use
- High-level language Separate from the low-level
processor operations closer to human language
than machine language - "Programming at the speed of thought"
- Increases productivity
- Python programs three to five times shorter than
Java - Python programs five to ten times shorter than
C
7Python Is Easy to Use (continued)
- Python Program
- print "Game Over!"
- C Program
- include ltiostreamgt
- int main()
-
- stdcout ltlt "Game Over!" ltlt stdendl
- return 0
-
8Python Is Powerful
- Used by large organizations
- NASA
- Google
- Microsoft
- Used in published games
- Battlefield 2
- Civilization IV
- Disneys Toontown Online
9Python Is Object-Oriented
- Object-oriented programming (OOP) Methodology
that defines problems in terms of objects that
send messages to each other - In a game, a Missile object could send a Ship
object a message to Explode - OOP not required, unlike Java and C
10Python Is a Glue Language
- Can be integrated with other languages
- C/C
- Java
- Use existing code
- Leverage strengths of other languages
- Extra speed that C or C offers
11Python Runs Everywhere
- Platform independent Independent of the specific
computer operating system - Python runs on
- Windows
- DOS
- Mac OS
- Linux
- Many more
12Python Has a Strong Community
- As an approachable language, has approachable
community - Python Tutor mailing list
- http//mail.python.org/mailman/listinfo/tutor
- Perfect for beginners
- No actual "tutors" or "students"
13Python Is Free and Open Source
- Open source Publicly available open source
software typically programmed by volunteers
anyone can use source code without fee - Can modify or even resell Python
- Embracing open-source ideals is part of what
makes Python successful
14Setting up Python on Windows
- The book suggests using the CD-ROM it came with,
but that version of Python (2.3.5) is old now - Instead, follow the instructions on the class web
page - Go to http//www.python.org/download/
- Download the latest standard (aka production)
release installer (.msi file) - Double-click the installer program and follow its
instructions to install Python on your boot (C)
drive
15Setting up Python on Windows
Figure 1.2 Python 2.3.5 Installation Dialogue
under Windows Your computer is soon to be home to
Python.
16Setting up Python on Other Operating Systems
- Linux
- Python probably already installed
- Test try running python at command prompt
- If not installed, go to http//www.python.org/down
load/ (you will probably need to build from
source) - Mac OS 10.5.x
- Leopard (10.5.x) already has Python 2.5.1
installed, but you need to install IDLE.app
following instructions at http//wiki.python.org/m
oin/MacPython/Leopard - Earlier Mac OS X and other systems
- If necessary, download appropriate version from
Python web site at http//www.python.org/download/
17Introducing IDLE
- Integrated Development Environment (IDE)
Application that helps software developers write
programs - Like a word processor for your code
- IDE that ships with Python
- Has two modes Interactive and Script
18Programming in Interactive Mode
Figure 1.4 Python in interactive mode Python
awaits your command.
19Programming in Interactive Mode (continued)
- Great for immediate feedback
- Test a simple idea
- Remember how something works
- Open Python in interactive mode
- In Windows, from the Start menu, choose Programs,
Python ltversiongt, IDLE (Python GUI) - On STC Lab machines
- Windows Will be in Start menu gt All Programs gt
Departmentally Sponsored gt Informatics - Mac Type python in /Applications/Utilities/Termin
al.app or run IDLE.app from the Developer Tools
folder in the Dock
20Programming in Interactive Mode (continued)
- At command prompt (gtgtgt), type print "Game Over"
- Python responds with Game Over
21Programming in Interactive Mode (continued)
- print Statement can display a string (actually,
any expression) - String Sequence of characters
- Statement Single unit in programming language
that performs some action - print "Game Over"
- Expression Something which has a value or that
can be evaluated to a single value - "Game Over"
- 7 2
- Code Sequence of programming statements
22Programming in Interactive Mode (continued)
- Syntax highlighting Displaying programming code
in different colors or fonts, according to the
category of each item - Errors
- Computers take everything literally
- primt "Game Over" produces an Error Message
SyntaxError invalid syntax - Syntax error Error in the rules of usage often
a typo - Bug Error in programming code
23(No Transcript)
24Programming in Script Mode
Figure 1.5 Python in script mode Your blank
canvas awaits.
25Programming in Script Mode (continued)
- Great for programs you want to run later
- Write, edit, save, and load programs
- Like word processor for your programs
- Find and replace
- Cut and paste
- Open a script window
- In interactive window, select File menu, New
Window
26Programming in Script Mode (continued)
- Write program
- In script window, type print "Game Over"
- Save program
- Select File, Save As, name game_over.py
- Always save before running
- Run Program
- Select Run, Run Module
- Results displayed in interactive window
27Programming in Script Mode (continued)
- Figure 1.6 Python after a script has been run
- The results of running the Game Over program
28The Game Over Program
- Game Over
- Demonstrates the print command
- print "Game Over"
- raw_input("\n\nPress the enter key to exit.")
29The Game Over Program (continued)
- Comment Note in source code meant only for
programmers ignored by computer - Start comment with
- Use opening block of comments
- Blank Lines
- Also (generally) ignored by computer
- Use for readability keep related code together
- Console Window
- Final line keeps console window open
30Summary
- Python is a high-level, object-oriented
programming language thats powerful yet easy to
use - Python can interface with other programming
languages - IDLE is Pythons standard IDE
- IDLE has an interactive mode that offers
immediate response to Python code - IDLE has a script mode that allows programmers to
write, edit, load, save, and run their programs
31Summary (continued)
- A string is a sequence of characters
- A statement is a single unit of programming that
performs some action - The print statement displays strings on the
screen - An expression is something which has a value or
that can be evaluated to a single value - Syntax highlighting is displaying programming
code in different colors or fonts, according to
the category of each item
32Summary (continued)
- A syntax error is a violation of the grammar of a
programming language often caused by a typo - A bug is an error in programming code
- A comment is a note in source code meant only for
programmers ignored by computer - Comments start with
- You should use an opening block of comments in
your programs to identify the programmer, the
creation date, and the programs purpose
33Guide to Programming with Python
- Chapter Two
- Types, Variables, and Simple I/O The Useless
Trivia Program
34Objectives
- Use triple-quoted strings and escape sequences
- Make programs do math
- Store data in the computers memory
- Use variables to access and manipulate that data
- Get input from users to create interactive
programs
35The Useless Trivia Program
- Figure 2.1 Sample run of the Useless Trivia
program - Whoa! Steve might think about a diet before he
visits the sun.
36Using Quotes with Strings
- Can create a single string that's paragraphs long
- Can format text of string in a specific manner
- Can use quotes to create long string or to format
37The Game Over 2.0 Program
- Figure 2.2 Sample run of the Game Over 2.0
program - Ah, the game is really over.
38Using Quotes
- Using quotes inside strings
- Define with either single (') or double quotes
(") - 'Game Over' or "Game Over"
- Define with one type, use other type in string
- "Program 'Game Over' 2.0"
- Triple-quoted strings can span multiple lines
- """
- I am a
- triple-quoted string
- """
- Line-continuation character \
39Using Escape Sequences with Strings
- Escape sequence Set of characters that allow you
to insert special characters into a string - Backslash followed by another character
- e.g. \n
- Simple to use
40The Fancy Credits Program
- Figure 2.3 Sample run of the Fancy Credits
program - So many people to thank, so many escape sequences
41Escape Sequences
- System bell
- print "\a"
- Tab
- print "\t\t\tFancy Credits"
- Backslash
- print "\t\t\t \\ \\ \\ \\ \\ \\ \\"
- Newline
- print "\nSpecial thanks goes out to"
- Quote
- print "My hair stylist, Henry \'The Great\', who
never says \"can\'t\"."
42Escape Sequences (continued)
- Table 2.1 Selected escape sequences
43Concatenating and Repeating Strings
- Can combine two separate strings into larger one
- Can repeat a single string multiple times
44The Silly Strings Program
- Figure 2.4 Sample run of the Silly Strings
program - Strings appear differently than in the program
code.
45Concatenating Strings
- String concatenation Joining together of two
strings to form a new string - When used with string operands, is the string
concatenation operator - "concat" "enate"
- Suppressing a Newline
- When used at the end of print statement, comma
suppresses newline - print "No newline after this string",
46Repeating String
- Multiple concatenations
- When used with strings, creates a new string by
concatenating a string a specified number of
times - Like multiplying a string
- "Pie" 10 creates new string "PiePiePiePiePiePieP
iePiePiePie"
47Working with Numbers
- Can work with numbers as easily as with strings
- Need to represent numbers in programs
- Score in space shooter game
- Account balance in personal finance program
- Python can represent different types of numbers
48The Word Problems Program
- Figure 2.5 Sample run of the Word Problems
program - With Python, you can keep track of a pregnant
hippos weight.
49Numeric Types
- Type Represents the kind of value determines
how the value can be used - Two common numeric types
- Integers Numbers without a fractional part
- 1, 0, 27, -100
- Floating-Point Numbers (or Floats) Numbers with
a fractional part - 2.376, -99.1, 1.0
50Mathematical Operators
- Addition and Subtraction
- print 2000 - 100 50 displays 1950
- Integer Division
- print 24 / 6 displays 4
- But print 19 / 4 displays 4 as well
- Result of integer division always integer
- Floating-Point Division
- print 19.0 / 4 displays 4.75
- When at least one number is a float, result is a
float - Modulus (remainder of integer division)
- print 107 4 displays 3
51Mathematical Operators (continued)
- Table 2.2 Mathematical operators with integers
52Mathematical Operators (continued)
- Table 2.3 Mathematical operators with floats
53Understanding Variables
- Variable Represents a value provides way to get
at information in computer memory - Variables allow you to store and manipulate
information - You can create variables to organize and access
this information
54The Greeter Program
- Figure 2.6 Sample run of the Greeter program
- Using a variable for the name
55Creating Variables
- Assignment statement Assigns a value to a
variable creates variable if necessary - name "Larry"
- Stores string "Larry" in computer memory
- Creates variable name
- Assigns value so that name refers to "Larry"
56Using Variables
- Use variable where you want value it represents
- print name or print "Larry"
- Both display Larry
- print "Hi, " name or print "Hi, Larry"
- Both display Hi, Larry
57Naming Variables
- Rules for legal variable names
- Can contain only numbers, letters, and
underscores - Cant start with a number
- Cant be a keyword
- Keyword Built-in word with special meaning
- Legal Names
- velocity, player2, max_health
- Illegal Names
- ?again, 2nd_player, print
58Naming Variables (continued)
- Guidelines for good variable names
- Choose descriptive names score instead of s
- Be consistent high_score or highScore
- Follow traditions Names that begin with
underscore have special meaning - Keep the length in check personal_checking_account
_balance - too long? - Self-documenting code Code written so that its
easy to understand, independent of any comments
59Getting User Input
- Variables important for
- Getting user input
- Storing user input
- Manipulating user input
60The Personal Greeter Program
- Figure 2.7 Sample run of the Personal Greeter
program - name is assigned a value based on what the user
enters.
61Getting User Input
- Function A named collection of programming code
that can receive values, do some work, and return
values - Argument Value passed to a function
- Return value Value returned from a function upon
completion - Function is like a pizzeria
- Make a call
- Provide information (like pepperoni)
- Get something back (like a hot pepperoni pizza)
62Getting User Input (continued)
- raw_input() function
- Prompts the user for text input
- Returns what the user entered as a string
- name raw_input("Hi. What's your name? ")
- Uses argument "Hi. What's your name? " to prompt
user - Returns what user entered as a string
- In assignment statement, name gets returned
string
63Using String Methods
- String methods allow you to do many things,
including - Create new strings from old ones
- Create string thats all-capital-letters version
of original - Create new string from original, based on letter
substitutions
64The Quotation Manipulation Program
- Figure 2.8 Sample run of the Quotation
Manipulation program - The slightly low guess is printed several times
with string methods.
65String Methods
- Method A function that an object has
- Use dot notation to call (or invoke) a method
- Use variable name for object, followed by dot,
followed by method name and parentheses - an_object.a_method()
- Strings have methods that can return new strings
66String Methods (continued)
- quote "I think there is a world market for
maybe five computers." - print quote.upper()
- I THINK THERE IS A WORLD MARKET FOR MAYBE FIVE
COMPUTERS. - print quote.lower()
- i think there is a world market for maybe five
computers. - print quote.title()
- I Think There Is A World Market For Maybe Five
Computers. - print quote.replace("five", "millions of")
- I think there is a world market for millions of
computers. - Original string unchanged
- print quote
- I think there is a world market for maybe five
computers.
67String Methods (continued)
- Table 2.4 Useful string methods
68Using the Right Types
- Important to know which data types are available
- Equally important to know how to work with them
- If not, might end up with program that produces
unintended results
69The Trust Fund BuddyBad Program
- Figure 2.9 Sample run of the Trust Fund
Buddy-Bad program - The monthly total should be high, but not that
high.
70Logical Errors
- Logical Error An error that doesnt cause a
program to crash, but instead produces unintended
results - Program output that looks like very large number
200001000017000500075001200068001000 - Remember, raw_input() returns a string, so
program is not adding numbers, but concatenating
strings
71Logical Errors (continued)
- car raw_input("Lamborghini Tune-Ups ")
- rent raw_input("Manhattan Apartment ")
- jet raw_input("Private Jet Rental ")
- gifts raw_input("Gifts ")
- food raw_input("Dining Out ")
- staff raw_input("Staff (butlers, chef, driver,
assistant) ") - guru raw_input("Personal Guru and Coach ")
- games raw_input("Computer Games ")
- total car rent jet gifts food staff
guru games - car, rent, jet, gifts, food, staff, guru, games
are strings - total is concatenation of all strings
72Converting Values
- Can convert one type of value to another
- Use built-in functions
- Solution to Trust Fund BuddyBad program
73The Trust Fund BuddyGood Program
- Figure 2.10 Sample run of the Trust Fund
Buddy-Good program - Now the total is right.
74Converting Types
- int() function converts a value to an integer
- car raw_input("Lamborghini Tune-Ups ")
- car int(car)
- Can nest multiple function calls
- rent int(raw_input("Manhattan Apartment "))
75Converting Types (continued)
- Table 2.5 Selected type conversion functions
76Augmented Assignment Operators
- Common to assign a value to a variable based on
its original value - For example, increment value of variable
- Augmented assignment operators provide condensed
syntax - Original score score 1
- Augmented score 1
77Augmented Assignment Operators (continued)
- Table 2.6 Useful augmented assignment operators
78Printing Multiple Values
- To print multiple values in single print
statement, separate values by commas - print "\nGrand Total ", total
79Summary
- String can be defined with either single or
double quotes - Tripled-quoted strings, defined by three opening
and closing quotes, can span multiple lines - An escape sequence is a set of characters that
allow you to insert special characters into a
string - String concatenation is the joining together of
two strings to form a new string - Integers, whole numbers with no decimal part, and
floats, numbers with a decimal part, are two
numeric types
80Summary (continued)
- Result of integer division is always an integer
while result of floating-point division is always
a float - A variable represents a value and provides way to
get at information in computer memory - An assignment statement assigns a value to a
variable and creates variable if necessary - A function is a named collection of programming
code that can receive values, do some work, and
return values - The raw_input() function prompts the user for
input and returns what the user entered as a
string
81Summary (continued)
- A method is a function that an object has
- Strings have methods that can return new strings
- A logical error produces unintended results
- Python has functions for converting values to an
integer, a float, or a string - Augmented assignment operators provide condensed
syntax for changing the value of a variable based
on its original value