2. * Note: All of the material for the Required Textbook, Optional Textbook are protected by Copyright Law. * Professor Sana Odeh’s notes and programs listed here are copyrighted as well. 1 Class # 2: Introduction to programming using Python Course: Introduction to Computers and Programming using Python V22.0002, Section 3, Spring 2010 Professor: Sana Odeh odeh@courant.nyu.edu Office hours: Mondays 2:00 pm - 4 pm, room 321 in Courant (this building), or at other times by appointment Course website: http://www.cs.nyu.edu/courses/spring10/V22.0002- 003/index.html odeh@courant.nyu.edu http://www.cs.nyu.edu/courses/spring10/V22.0002- 003/index.html

3. * Note: All of the material for the Required Textbook, Optional Textbook are protected by Copyright Law. * Professor Sana Odeh’s notes and programs listed here are copyrighted as well. 2 Introduction What are Programming Languages Introductions to Python Programming basics Introduce the basic structure of Python program How to use python software (Idle) How to design/create/edit/execute/run and debug our Python programs

4. * Note: All of the material for the Required Textbook, Optional Textbook are protected by Copyright Law. * Professor Sana Odeh’s notes and programs listed here are copyrighted as well. 3 What is a program Program is a set of instructions that performs calculations/computation You can also think of programs as software that perform specific tasks allowing you to do the following: Buy products on the web Type reports using MS Word Chat with friends using the iphone Post an album on FaceBook Listen to music using your ipod Play games

5. * Note: All of the material for the Required Textbook, Optional Textbook are protected by Copyright Law. * Professor Sana Odeh’s notes and programs listed here are copyrighted as well. 4 What is a program Programmers like to find recipe (algorithm) for every thing (including intelligence) The focus of programming is to solve problems So we need to develop an algorithm (a solution) Solutions should be clear, efficient, concise (no ambiguity) So, the mathematical algorithm (recipe ) for finding the average for 2 numbers is (a+b)/2 Now, we can write a program to find the average using this algorithm We need to translate this algorithm to a high-level programming language (sentences are written similar to English) average = (80 + 100)/ 2 The above statement is similar to how you write a statement in java, C, C++, Ruby, JavaScript, Perl

6. * Note: All of the material for the Required Textbook, Optional Textbook are protected by Copyright Law. * Professor Sana Odeh’s notes and programs listed here are copyrighted as well. 5 So let’s look at how we can write a program A simple in python # my first program in python: let’s print 'hello' on the screen print ("hello") This will print the following to the screen: hello

7. * Note: All of the material for the Required Textbook, Optional Textbook are protected by Copyright Law. * Professor Sana Odeh’s notes and programs listed here are copyrighted as well. 6 Anatomy of a python program Comments Variables Statements Functions Identifiers keywords

8. * Note: All of the material for the Required Textbook, Optional Textbook are protected by Copyright Law. * Professor Sana Odeh’s notes and programs listed here are copyrighted as well. 7 Anatomy of a python program Comments (Good Style): Comments are ignored by the compiler. Makes program easy to read and debug (very important in software development). Provides information about your program and significant segments of code that performs action/computation You should provide comments at the beginning of every program and give the following information: Your name, assignment #, and a brief sentence about the purpose of the program) Here is an example of a first line(s) comment (multiple lines comment) “”” Name: Barack Obama. Homework #1 Program provide an algorithm/solution to fix the US economy “” You should provide one line comments to explain a segment of code (every 5 lines or so whenever you have to perform a specific and important action in you program) # Compute the for average IQ for the last three US presidents avgiq = (obamaiq + bushiq + Clintoniq)/3

9. * Note: All of the material for the Required Textbook, Optional Textbook are protected by Copyright Law. * Professor Sana Odeh’s notes and programs listed here are copyrighted as well. 8 Anatomy of a python program Statements One line of code that performs a specific actions such as assignment avgiq = (obamaiq + bushiq + Clintoniq)/3 Or number = 20 Or name = “Obama”

10. * Note: All of the material for the Required Textbook, Optional Textbook are protected by Copyright Law. * Professor Sana Odeh’s notes and programs listed here are copyrighted as well. 9 Functions Functions are mini programs (small modules) that perform specific actions(s) You can build functions for sorting, searching, computing calculations such as average, and finding whether a number is even or odd 1. Functions can already defined and included with the python software (Built-in ). Many useful functions are available for you to use in your programs such as print() and input() functions. You can simply use in your programs to perform a specific action such as print, perform mathematical operations (square numbers, find sqrt and so on) Example: print(“ I hope you are NOT sleeping”) Example2: To ask user to enter data (numbers, strings), you can use the following function: input(“Mr President, Do you think you are doing a good job so far?”) 2. Functions can be defined by the programmer (User- Defined) will learn how to do this later on They can be called methods in other programming languages

11. * Note: All of the material for the Required Textbook, Optional Textbook are protected by Copyright Law. * Professor Sana Odeh’s notes and programs listed here are copyrighted as well. 10 Variables: labels (a location in memory that points/holds one piece of data (one value ) Locations in memory that holds one piece of data Numbers: (floating-point numbers and whole numbers) -200 (integers- whole numbers without any decimal values) 20.90 (floating-point numbers ) Text: (String) One or more character name = “Avatar” message = “Hello there”)

12. * Note: All of the material for the Required Textbook, Optional Textbook are protected by Copyright Law. * Professor Sana Odeh’s notes and programs listed here are copyrighted as well. 11 Memory Concepts/Variables (simple definition) Bucket Analogy It is useful to think of a variable for now as a bucket holding one piece of data ( a number or a string). The bucket has a unique name, and can only hold certain kinds of data. price 200.30 Price is a variable containing the value 200.30, and can contain only integers.

13. * Note: All of the material for the Required Textbook, Optional Textbook are protected by Copyright Law. * Professor Sana Odeh’s notes and programs listed here are copyrighted as well. 12 Reserved Words Reserved words or keywords are words that have a specific meaning to the compiler and cannot be used in the program. Reserved words in python: – if – elif – and – Or – for – while

14. * Note: All of the material for the Required Textbook, Optional Textbook are protected by Copyright Law. * Professor Sana Odeh’s notes and programs listed here are copyrighted as well. 13 Python Reserved Words Reserved words in python version 3: Let’s print a list of keywords now using python interactive commands (at the python prompt >>>, you can type commands) >>> import keyword >>> print (keyword.kwlist) 'False', 'None', 'True', 'and', 'as', 'assert', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield'

15. * Note: All of the material for the Required Textbook, Optional Textbook are protected by Copyright Law. * Professor Sana Odeh’s notes and programs listed here are copyrighted as well. 14 Identifier –Name or labels you can give to names of programs, variables or functions called identifier ( in this case its hello) Series of characters consisting of letters, digits, underscores ( _ ) Must begin with a letter or underscore Does not begin with a digit Should not include spaces Letters are case sensitive (Name is not the same as name) Examples: Welcome1, value, _value, button7 –2num is invalid –Butt on is invalid Pythonis case sensitive (capitalization matters) –a1 and A1 are different

16. * Note: All of the material for the Required Textbook, Optional Textbook are protected by Copyright Law. * Professor Sana Odeh’s notes and programs listed here are copyrighted as well. 15 Programming Errors Syntax Errors –Detected by the compiler Runtime Errors –Causes the program to abort Logic Errors –Produces incorrect result

17. * Note: All of the material for the Required Textbook, Optional Textbook are protected by Copyright Law. * Professor Sana Odeh’s notes and programs listed here are copyrighted as well. 16 Syntax Errors Caused when the compiler cannot recognize a statement. These are violations of the language The compiler normally issues an error message to help the programmer locate and fix it Also called compile errors or compile-time errors. For example, if you forget a quotation mark or a parenthesis needed for print(), you will get a syntax error. print(“hello)

18. * Note: All of the material for the Required Textbook, Optional Textbook are protected by Copyright Law. * Professor Sana Odeh’s notes and programs listed here are copyrighted as well. 17 Run-time Errors Other major kind of error you’ll see Happens when a program is running The compiler cannot identify these errors at compile time. Will talk more about these later i = 1 / 0

19. * Note: All of the material for the Required Textbook, Optional Textbook are protected by Copyright Law. * Professor Sana Odeh’s notes and programs listed here are copyrighted as well. 18 Logic Errors –Produces incorrect result double average = 80.0 + 90.0 / 2 This program produces in correct answer of 90.0/2 + 80.0 = 45 + 80.0 = 125.0 Answer should be (80.0 + 90.0)/2 170.0/2 = 85.0

20. * Note: All of the material for the Required Textbook, Optional Textbook are protected by Copyright Law. * Professor Sana Odeh’s notes and programs listed here are copyrighted as well. 19 Arithmetic +Addition 2 +2 = 4 *Multiplication 2 * 2 = 4 -Subtractions 2 - 2 =0 /Division 3/2 = 1.5 **Power 2**3 = 8 //Division but will truncates decimal values (NO decimal values) 3 // 2 = 1 %MOD/ Moduls: Returns the remainder from a division 3 % 2 = 1

21. * Note: All of the material for the Required Textbook, Optional Textbook are protected by Copyright Law. * Professor Sana Odeh’s notes and programs listed here are copyrighted as well. 20 Simple program to add two numbers # Program will initialize variables and add two numbers # Specify values for num1 and num2 (initialization variables) num1 = 2 num2 = 3 # Adding two numbers and storing result in a variable called "sum" sum = num2 + num1 # Printing numbers and the sum of two numbers print("num1 has a value of ", num1) print("num2 has a value of ", num2) print("The sum of num1 + num2 is ", sum)