Basics of Programming through Python PDF

Imam Abdulrahman Bin Faisal University Deanship of Preparatory Year and Supporting Studies Basics of Programming through Python Why should you learn to write programs? Introduction to Programming...

Imam Abdulrahman Bin Faisal University Deanship of Preparatory Year and Supporting Studies Basics of Programming through Python Why should you learn to write programs? Introduction to Programming COMP105 Term2 2024-2025 Learning outcomes ▪ Discuss why we need to learn programming. ▪ Understand the basic building blocks of programs in Python. 2 Test your Knowledge ▪ What is the difference between variables and constants? ▪ What do you know about data types in PL (Programing Languages)? ▪ What do you know about the input of any program? 3 Uunderstanding programming Programming ▪ You need two skills to be a programmer: ▫ First: ▫ You need to know the programming language (Python) - you need to know the vocabulary and the grammar. ▫ You need to be able to spell the words in this new language properly and know how to construct well- formed “sentences” in this new language. 5 Programming ▫ Second, you need to “tell a story”. ▫ In writing a story, you combine words and sentences to convey an idea to the reader. ▫ There is a skill and art in constructing the story, and skill in story writing is improved by doing some writing and getting some feedback. ▫ In programming, our program is the “story” and the problem you are trying to solve is the “idea”. 6 Programming ▪ Once you learn one programming language such as Python, you will find it much easier to learn a second programming language (PL) such as JavaScript, C, C++, … ▪ The new programming language has very different vocabulary and grammar, but the problem-solving skills will be the same across all programming languages (PL). 7 Terminology: Interpreter and compiler Terminology ▪ Python is a high-level language intended to be relatively for humans to read and write and for computers to read and process. ▪ The actual hardware inside the Central Processing Unit (CPU) does not understand any of these high-level languages. ▪ Instead, we build various translators to allow programmers to write in high-level languages like Python or JavaScript and these translators convert the programs to machine language for actual execution by the CPU. 9 Terminology ▪ These programming language translators fall into two general categories:(1) interpreters and (2) compilers. ▪ An interpreter reads the source code of the program as written by the programmer, parses the source code, and interprets the instructions on the fly. ▫ Python is an interpreter and when we are running Python interactively, we can type a line of Python (a sentence) and Python processes it immediately and is ready for us to type another line of Python. 10 Terminology ▪ A compiler needs to be handed the entire program in a file, and then it runs a process to translate the high-level source code into machine language and then the compiler puts the resulting machine language into a file for later execution. ▪ It is not easy to read or write machine language, so it is nice that we have interpreters and compilers that allow us to write in high-level languages like Python or C. 11 Python Program ▪ Typing commands into the Python interpreter is a great way to experiment with Python’s features, but it is not recommended for solving more complex problems. ▪ When we want to write a program, we use a text editor to write the Python instructions into a file, which is called a script. ▫ By convention, Python scripts have names that end with.py. 12 The building blocks of programs ▪ There are some low-level conceptual patterns that we use to construct programs. ▪ These constructs are not just for Python programs, they are part of every programming language from machine language up to the high-level languages. ▫ Input ▫ Output ▫ Sequential execution ▫ Conditional execution ▫ Repeated execution 13 ▫ Reuse The building blocks of programs ▪ Input: ▫ Get data from the “outside world”. ▫ This might be reading data from a file, or even some kind of sensor like a microphone or GPS. ▫ In our initial programs, our input will come from the user typing data on the keyboard. 14 The building blocks of programs ▪ Output: ▫ Display the results of the program on a screen or store them in a file or perhaps write them to a device like a speaker to play music or speak text. ▪ Sequential execution: ▫ Perform statements one after another in the order they are encountered in the script. 15 The building blocks of programs ▪ Conditional execution: ▫ Check for certain conditions and then execute or skip a sequence of statements. ▪ Repeated execution: ▫ Perform some set of statements repeatedly, usually with some variation. ▪ Reuse: ▫ Write a set of instructions once and give them a name and then reuse those instructions as needed throughout your program. 16 What could possibly go wrong? Errors / Exceptions ▪ As your programs become increasingly sophisticated, you will encounter three general types of errors: ▫ Syntax errors ▫ Logic errors ▫ Semantic errors 18 Errors / Exceptions ▪ Syntax errors: ▫ These are the first errors you will make and the easiest to fix. ▫ A syntax error means that you have violated the “grammar” rules of Python. ▫ Python does its best to point right at the line and character where it noticed it was confused. ▫ The line and character that Python indicates in a syntax error may just be a starting point for your investigation. 19 Syntax errors: Example >>> primt 'Hello world!' >>> I love you Python! File "", line 1 File "", line 1 primt 'Hello world!' I love you Python! SyntaxError: invalid syntax SyntaxError: invalid syntax >>> primt ('Hello world') >>> if you come out of there, I would Traceback (most recent call last): teach you a lesson File "", line 1, in File "", line 1 NameError: name 'primt' is not if you come out of there, I would defined teach you a lesson SyntaxError: invalid syntax 20 Errors / Exceptions ▪ Logic errors: ▫ A logic error is when your program has good syntax but there is a mistake in the order of the statements or perhaps a mistake in how the statements relate to one another. ▫ A good example of a logic error might be: ▫ “take a drink from your water bottle, put it in your backpack, walk to the library, and then put the top back on the bottle.” 21 Logic Errors: Example x=3 y=2 line 3, in print(z) print(z) NameError: name 'z' is not defined z=x+y 22 Errors / Exceptions ▪ Semantic errors: ▫ A semantic error is when your description of the steps to take is syntactically perfect and in the right order, but there is simply a mistake in the program. ▫ The program is perfectly correct, but it does not do what you intended for it to do. 23 Semantic errors: Example x=3 y=2 Operator in this example should be (+) but by mistake (-) z=x-y print(z) No Error Messgae displayes , and the program Run correctly 24 Errors / Exceptions ▪ When Python spits out an error or even when it gives you a result that is different from what you had intended, then begins the hunt for the cause of the error. ▪ Debugging is the process of finding the cause of the error in your code. 25 Thanks! Any questions? 26