1 Programming for Engineers in Python Autumn Lecture 2: More Basics

2 Lecture 1: Highlights Functions Control structures (if/else) Strings

3 Today Leftovers from last week Compiler, interpreter Variables, types, operators, scope

4 Installing and Running Python 2.7 Python 2.7 is already installed in the computers’ classroom Install: Windows 32 bit: A “Python 2.7” folder will be created in your Start Menu: IDLE (Python GUI)‎ - recommended working environment ‏ Python (command line)‎ - textual Python interpreter (a little faster, less convenient) Working with IDLE video:

5 String Type

6 Strings Structure

7 Slicing olleH

8 Lists

9 Iterating Over Lists for var in list: print(var) value in list while loop in tirgul

10 Lists Built In Methods

11 Range, Sum

12 Abstruse Goose, Computer Programming 101,Computer Programming 101

13 Abstruse Goose, Under The HoodUnder The Hood

14 Machine Code (Language) Computers understand only machine language Basically looks like a sequence of 1’s and 0’s Very inconvenient to work with and non intuitive All other computer languages were created for human convenience The computer does not understand C/C#/Java/Scala Must be “translated” into machine language

15 Programming Languages Basics A computer program is a sequence of instructions (texts) that can be “understood" by a computer and executed by it A programming language is a machine-readable artificial language designed to express computations that can be performed by a computer

16 Compiler

17 Hello World (in C) ;-)

18 Interpreter

19 Interpreter Python is an interpreted programming language The Read/Evaluate/Print Loop Read an expression Compute its value Print the result Repeat the above

20 Language Selection and Python Goal Runtime vs. Development time Operating systems Platforms Python is appropriate for quick development of small-medium tasks: Experiments Data analysis Small projects Short development-execution rounds

21 Memory

22 Memory (Cont.) The computer memory is composed of a long list of bits Bits are grouped into bytes and words Every byte is numbered sequentially This number is called an address

23 Variables and Types משתנה (variable): יחידת מידע המאכסנת ערך במהלך ריצת התכנית ניתן ל"גשת" למשתנה: לשנות (לא תמיד) או לקבל את ערכו ניתן לבצע פעולות חשבוניות (ואחרות) בעזרת משתנים לכל משתנה מוגדר טיפוס (type) שקובע את אופן ביצוע הפעולות על המשתנה

24 Define Variables variable name value assignment operator Variable x “is of type” Int and is assigned the value 4

25 Why do We Need Variables? Computer programs manipulate data Data is given as input or calculated throughout the program To be later accessed, variables must be remembered Thus, variables are stored in the memory Variable name  memory address

26 Types Determine number of bytes in memory (“locker size”) Determine the operations that are defined for a given variable

27 Some Basic Types

28 Variables and Types

29 Why Do We Need Different Types? Saving memory Execution speed Defined operations Makes compiler “life” easier (not relevant in Python)

30 Arithmetic Operators

31 Example 1

32 Types and Casting

33 Example 3

34 Comparisons

35 Example 1

36 Example 2

37 Logical Operators and or not Truth Tables (1 – True, 0 - False)

38 Scope

Next Week – A Big Jump! A cape will not help – work hard!