Lecture 1 - MUH101 Introduction to Programming - PDF

Lecture 1 Welcome to MUH101 Burkay Genç, Ahmet Selman Bozkır, and Selma Dilek 20/02/2024 Today · course Info · what is computation · python basics · mathematical operations · python variables and types 2/46 Course Info · Subject : Learn Python a programming languag...

Lecture 1 Welcome to MUH101 Burkay Genç, Ahmet Selman Bozkır, and Selma Dilek 20/02/2024 Today · course Info · what is computation · python basics · mathematical operations · python variables and types 2/46 Course Info · Subject : Learn Python a programming language · Classes : - All classes are face-to-face - All off-class communication will be on Hacettepe University Digital Learning Platform (HADİ) - hadi website - You have to follow hadi daily for new announcements 3/46 Course Info · Grading - 60%: Midterm (2x) - Midterms format will be announced during the semester - 40%: Final Exam (1x) 4/46 Course Info · You are strictly forbidden to cooperate on exams · You are strictly forbidden to search for answers on the Internet · You are strictly forbidden to copy/paste materials from the Internet 5/46 COURSE POLICIES · Cooperation - you may cooperate with your friends to understand the course material - all exam work needs to be individual - cheaters will be harshly penalized -> -100, F3, disciplinary committee 6/46 FAST PACED COURSE · Position yourself to succeed! - do practice early - do not skip lectures · New to programming? PRACTICE. PRACTICE? PRACTICE! - can’t passively absorb programming as a skill - download code before lecture and follow along - don’t be afraid to try out Python commands! 7/46 TOPICS · represent knowledge with data structures · iteration and recursion as computational metaphors · abstraction of procedures and data types · organize and modularize systems using object classes and methods · [maybe] different classes of algorithms, searching and sorting · [maybe] complexity of algorithms 8/46 WHERE TO GET PYTHON · You can download your own copy, it is free - Download Python recommended · More advanced tasks (data science, machine learning) - Download Anaconda - Not recommended at this level · You can use online compilers/IDEs - Google Colab recommended will be used in course - Jupyter Notebook recommended - Python Fiddle - PyFiddle - Programiz · Use a Linux distribution such as Ubuntu, Manjaro etc. - Python comes built in 9/46 PYTHON IDE · What is an IDE? - An Integrated Development Environment allows you to write programs in a programming language and provides extra tools to help the process - Syntax highlighting - Code completion - Bracket completion/matching - Debugging - Profiling - more… · PyCharm is a very powerful and popular IDE for Python · IDLE comes built-in with any Python distribution · Eric, Spyder, Eclipse+PyDev · Sublime Text, VS Code, Atom, etc. are generic editors that can be extended with Python capabilities 10/46 WHAT DOES A COMPUTER DO · Fundamentally: - performs calculations a billion calculations per second! - remembers results 100s of gigabytes of storage! · What kinds of calculations? - built-in to the language - ones that you define as the programmer · computers only know what you tell them 11/46 TYPES OF KNOWLEDGE · declarative knowledge is statements of fact. - someone will win a Trophy before class ends · imperative knowledge is a recipe or “how-to”. 1. Students sign up for lottery 2. Burkay opens his IDE 3. Burkay chooses a random number between 1st and nth responder 4. Burkay finds the number in the responders sheet. Winner! 12/46 A NUMERICAL EXAMPLE · square root of a number x is y such that y ∗ y = x · recipe for deducing square root of a number x 1. Start with a guess, g 2. If g ∗ g is close enough to x, stop and say g is the answer 3. Otherwise make a new guess by averaging g and x/g 4. Using the new guess, repeat process until close enough g g ∗ g x/g (g + x/g)/2 3 9 16/3 4.17 4.17 17.36 3.837 4.0035 4.0035 16.0277 3.997 4.000002 13/46 WHAT IS A RECIPE 1. sequence of simple steps 2. flow of control process that specifies when each step is executed 3. a means of determining when to stop 1 + 2 + 3 = an algorithm! 14/46 COMPUTERS ARE MACHINES · how to capture a recipe in a mechanical process · fixed program computer - calculator · stored program computer - machine stores and executes instructions 15/46 BASIC MACHINE ARCHITECTURE Basic machine architecture 16/46 STORED PROGRAM COMPUTER · sequence of instructions stored inside computer - built from predefined set of primitive instructions - arithmetic and logic - simple tests - moving data · special program (interpreter) executes each instruction in order - use tests to change flow of control through sequence - stop when done 17/46 BASIC PRIMITIVES · Turing showed that you can compute anything using 6 primitives · modern programming languages have more convenient set of primitives · we can also create new primitives · anything computable in one language is computable in any other programming language - Python == Java == C == Pascal == C++ == C# - They only differ in ease of doing something 18/46 CREATING RECIPES · a programming language provides a set of primitive constructs - 2, 4.8, ‘a’, “burkay”, TRUE, +, -, *, … · expressions are complex but legal combinations of primitives in a programming language - 2 + 4.7 - TRUE && FALSE - 3.0 + 2 / 5.4 · expressions and computations have values and meanings in a programming language 19/46 ASPECTS OF LANGUAGES · primitive constructs - English: words - programming language: numbers, strings, simple operators 20/46 ASPECTS OF LANGUAGES · syntax - English: “cat dog boy” not syntactically valid “cat hugs boy” syntactically valid - programming language: “hi”5 not syntactically valid 3.2 * 5 syntactically valid 21/46 ASPECTS OF LANGUAGES · static semantics is which syntactically valid strings have meaning - English: syntactically valid “I are hungry” but static semantic error - programming language: 3.2*5 syntactically valid 3+“hi” static semantic error 22/46 ASPECTS OF LANGUAGES · semantics is the meaning associated with a syntactically correct string of symbols with no static semantic errors - English: can have many meanings "Flying planes can be dangerous" - programming languages: have only one meaning but may not be what programmer intended - Trying to print the square of 5: x = 5 print(x * 2) ## 10 · Oops! The program runs, because there are no static semantic errors. But it doesn’t do the intended thing. Here is a corrected version: x = 5 print(x ** 2) ## 25 23/46 WHERE THINGS GO WRONG · syntactic errors - common and easily caught · static semantic errors - some languages check for these before running program - can cause unpredictable behavior · no static semantic errors but different meaning than what programmer intended - program crashes, stops running - program runs forever - program gives an answer but different than expected 24/46 EXAMPLES · syntactic errors print(3.a) SyntaxError: invalid syntax a = 5 3a + 2 SyntaxError: invalid syntax a - 3'a' SyntaxError: invalid syntax · static semantic errors 3 + 'a' TypeError: unsupported operand type(s) for +: 'int' and 'str' 25/46 PYTHON PROGRAMS · a program is a sequence of definitions and commands - definitions evaluated - commands executed by Python interpreter in a shell · commands (statements) instruct interpreter to do something · can be typed directly in a shell or stored in a file that is read into the shell and evaluated 26/46 OBJECTS · programs manipulate data objects · objects have a type that defines the kinds of things programs can do to them - Burkay is a human so he can walk, speak English, etc. - Chewbacca is a wookie so he can walk, “mwaaarhrhh”, etc. · objects are - scalar (cannot be subdivided) - non-scalar (have internal structure that can be accessed) 27/46 SCALAR OBJECTS · int – represent integers, ex. 5 · float – represent real numbers, ex. 3.27 · bool – represent Boolean values True and False · NoneType – special and has one value, None · can use type() to see the type of an object type(5) ## type(3.0) ## 28/46 NON-SCALAR OBJECTS · Strings are non-scalar objects. They have internal structures. name = "burkay" print(name[2:4]) ## rk · We can construct new non-scalar objects. · Object oriented programming is the art of programming using non-scalar objects. 29/46 TYPE CONVERSIONS (CAST) · We can convert object of one type to another - Not all types are convertible! · float(3) converts integer 3 to float 3.0 · int(3.9) truncates float 3.9 to integer 3 float(3) ## 3.0 int(3.9) ## 3 int("burkay") ## ValueError: invalid literal for int() with base 10: 'burkay' 30/46 PRINTING TO CONSOLE · to show output from code to a user, use print command print("Hello World!") ## Hello World! print(3 + 2) ## 5 print("My age is", 41) ## My age is 41 31/46 EXPRESSIONS · combine objects and operators to form expressions · an expression has a value, which has a type · syntax for a simple expression 32/46 OPERATORS ON ints and floats · i+j → the sum · i-j → the difference · i*j → the product · i/j → the division · For the sum, the difference and the product, if both objects are integers then the result is an integer. If one or both are floats, then the result is a float. · For the division the result is always a float. · i%j → the remainder when i is divided by j · i**j → i to the power of j 33/46 OPERATORS ON ints and floats 3 + 5 ## 8 3 - 5 ## -2 3 * 5 ## 15 3 / 5 ## 0.6 32 % 5 ## 2 3 ** 4 ## 81 34/46 SIMPLE OPERATIONS · parentheses are used to tell Python to prioritize operations 3 * (2 + 5) ## 21 · operator precedence without parentheses - ** - * - / - + and – executed left to right, as appear in expression 3 * 2 + 5 ## 11 35/46 BINDING VARIABLES AND VALUES · equal sign is an assignment of a value to a variable name # variable = value pi = 3.14159 pi_approx = 22/7 · value stored in computer memory · an assignment binds variable name to value · retrieve value associated with variable name by invoking the name, by typing pi pi ## 3.14159 pi_approx ## 3.142857142857143 36/46 MULTIPLE ASSIGNMENTS · you can assign multiple values to variables at once a, b = 3, 5 a ## 3 b ## 5 37/46 VARIABLE NAMING · it is important to use clear and understandable names for variables · also, using parenthesis in expressions helps with code readability a, b, c = 5, 8, 3.14 d = c * a ** 2 * b vs. r, h, pi = 5, 8, 3.14 V_cyl = pi * (r ** 2) * h 2 Vcyl = πr h 38/46 COMMENTS · you can enrich your code by adding comments - to add a comment, start a line with # - lines starting with # are ignored by Python # Radius, height and pi are defined r, h, pi = 5, 8, 3.14 # The volume of the cylinder is computed # Volume is equal to height times the base area V_cyl = pi * (r ** 2) * h 39/46 ABSTRACTING EXPRESSIONS · why give names to values of expressions? · to reuse names instead of values · easier to change code later pi = 3.14159 radius = 2.2 area = pi * (radius ** 2) print(area) ## 15.205295600000001 40/46 PROGRAMMING vs MATH · in programming, variables do not get automatically updated pi = 3.14159 radius = 2.2 # area of circle area = pi * (radius**2) print(area) ## 15.205295600000001 radius = radius + 1 print(radius) ## 3.2 print(area) ## 15.205295600000001 area = pi * (radius**2) print(area) ## 32.169881600000004 41/46 CHANGING BINDINGS · can re-bind variable names using new assignment statements · previous value may still be stored in memory but lost the handle for it · value for area does not change until you tell the computer to do the calculation again pi = 3.14 radius = 2.2 area = pi * (radius**2) radius = radius + 1 42/46 Exercise 1. What is printed when the code snippet below is executed? type(5) print(3.0 - 1) 1. 2. 2.0 3. then 2.0 4. nothing Try the code: https://www.tutorialspoint.com/python/online-python-compiler.php 43/46 Exercise 1. Which expression is allowed in Python? 1. x + y = 2 2. x*x = 2 3. 2 = x 4. xy = 2 44/46 Exercise 1. What is printed when the code snippet below is executed? a = 6 b = 7 c = 1 total = a + b + c print(total) c += 1 # Same as: c = c + 1 print(total) 1. 14 then 14 2. 14 then 15 3. 14 4. 15 45/46 Copyright Information These slides are a direct adaptation of the slides used for MIT 6.0001 course present (as of February 2020) on MIT OCW web site. Original work by: Ana Bell, Eric Grimson, and John Guttag. 6.0001 Introduction to Computer Science and Programming in Python. Fall 2016. Massachusetts Institute of Technology: MIT OpenCourseWare. License: Creative Commons BY-NC-SA. Adapted by and for: Assoc. Prof. Dr. Burkay Genç. MUH101 Introduction to Programming, Fall 2022 Hacettepe University, Computer Engineering Department. 46/46