Student Checklist

Below is a checklist for the minimal Python syntax and some key ideas in programming.

Basic data types

Numbers

• Integers and floats represent quantities and measurements.
• Arithmetic and math operations work on integers and floats.
• Integers are easier to represent than floats for a computer.

Strings

• Strings contain text and represent information like words, sentences, text as well labels, titles and names.
• In code strings are characters that are enclosed in single (') or double (") quotes.
• Strings are iterable by character. Exercises: print a string by character, reverse a string, count characters in a string.
• Operations with strings include concatenation, splitting, extracting parts, and modifying strings.
• Operators (+ and *), functions (like len()), and methods (like .lower()) work on strings.
• Multiline strings are enclosed in triple quotes and contain newlines as escape characters. They are good to make a string that is a poem.

Booleans

• Comparison operations result in a boolean value. These values are used as flags for decisions.
• A boolean can only be True or False.
• and and or operators combine booleans into logical expressions athat are useful for checking several conditions.

Conversion between types

• The str(), int(), float(), and bool() constructors allow conversion
  between types.
• Python automatically coerces types to minimize the conversions required but sometimes a programmer must do it. Example: input() returns a string, but you need a number.

Data structures

• Values of basic data types can be assembled into compound data types such as lists, tuples, and dictionaries.
• A list is a sequence of values of the same type: [7.5, 6.2, 5.1], ['Joe', 'Jane', 'Jim']. Python allows you to join different types of values in a list but you shouldn't.
• Tuple joins together several values of the same or different types: (25.5, 10.3) (2D coordinates), (7, "B") (airplane seat).
• Dictionaries are collections of key-value pairs. Using a dictionary you can look up of a value by its key.

Common operations on collections include:

• creating a collection,

• accessing an element (by an index in a list or a tuple or by key in a dictionary),

• subset or a slice of a collection,

• reusing a collection to create a new one.

• Collections can be nested. For example, a list can contain tuples: [(1, 2), (5, 5)].

Values and expressions

• A value is a small piece of data of a specific data type. 5 is an integer value, 0.33 is a float value, and "Life is wonderful" is a string value.
• Operations on values form an expression. An expression evaluates to a resulting value.
• Operations have order of precedence that you can clarify with parenthesis ().
• You can use Python REPL to write out and evaluate expressions.

Variables

Concept

• A variable is a named storage for a value that can be accessed throughout the program.
• You can bind a name to a value and refer to this value by that name later.

Assignment operation

• Another way of saying the same is that you assign a value to a variable with a specific name.
• Assignment operator = takes an expression on the right right, evaluates it and assigns a value to a variable on the left.

language = "Python"
message = language + " " + "is great!"
final_grade = (85+90+93)/3

• When unpacking tuples you can assign values to several variables at once: a, b = (3, 8).

Mutability

• In Python, all variables are mutable — you can change or reassign new values to them. x = 5; x = x + 1 works and x value becomes 6.

Naming

• There are requirements about what a valid variable name can be. my_age is ok.
• Choosing good variable names is not trivial and can be very subjective.

Comments

• Unlike in mathematics the value of the variables in programming are always known, they are not to be
  discovered by solving equations.
• Few other programming langiages use := or <- as assignment operator to highlight assignment is not equality.

Statements and code blocks

• Command to do something in a Python program is called a statement.
• A statement can occupy one line or span many lines.
• A program in Python is a series of statements that are executed as a sequence.
• A code block is a group of statements. They are used to create functions, loops, and conditional statements.
• In Python code blocks are defined by indentation (spaces at the start of a line).

Flow of programs

Conditions

• A condition is a check or comparison that evaluates to a boolean value.
• If a condition is true, it triggers one course of action; if it is false, other action will be taken. Conditions are used in if statements and while loops.

Conditional statements

• An if statement instructs the program to execute a code block only if a specified condition is true.
• if-else statements allow you to execute one block of code if a condition is true and another block if it is false.
• The elif keyword can be used to add multiple conditions. It is easy to overlook some condition in

while loops

• while loops repeat a code block as long as a condition remains true.
• They are useful for repeating actions until a certain condition is met.
• The actions inside the loop body usually affect the condition. (for example a counter or a user input).
• You can make an iternal loop with while True: and also exit the loop with break statement.

for loops

• for loops repeat a code block by choosing elements from a collection of items.
• They are often used to iterate over lists, tuples, or strings.
• You can also use for loop with range() function you know a specific number of times to run the loop.

for i in range(3)
   print(i)

Functions

What is it?

• Functions are reusable blocks of code that may take inputs (also called arguments), perform computations and actions, and can return an output value or return nothing.

Where is it&

• You define a function in one place of a program and run it later in one or more places. Running a function is also called 'invoking', or 'calling' a function.
• Function can be defined in a different file, then you have to import it.
• You are likely to use built-in functions, stardard library functions and third party library functions and also write your own functions.

What else about it?

• Functions can call other functions.
• Functions may have default parameter values.
• Function may have a short text description called a docstring.
• Function arguments and return value may be annotated to tell about types of variables used.

Good practice:

• You can start programming with a script and make own functions when you need to reuse some code block.
• Make a function that does one thing, clearly named and is easy to test.
• You can also separate functions that do calculations and the ones that communicate with outer world (printing, taking inputs, saving or reading files).

IO

Console

• print() prints text to the screen for the user to read.
• input() receives input from the user as a string.

Files

• Files can be opened, read, and written using Python's built-in functions open(), read(), and write().
• There is also a modern pathlib library in Python that makes handling files easier.

Reading from internet

• Not possible in the Pyodide programming enviroment that we use inthis course, but easy with httpx or requests libraries.

Errors and tests

Error handling

• Sometimes a program will encounter an impossible condition and stop its execution. These situations are called exceptions.
• Exception provide a message that tries to explain you what went wrong.
• Some errors would not cause exceptions, and you will need tests to add more guarantees your program is correct.

Unit testing

• Testing ensures that code behaves as expected.
• You can write simple assertions in code with assert followed by condition and convert them to tests later.
• A small test for a part of the code is called a 'unit test'.
• As experienced programmer you may write the test for you code before the code. This technique is called test driven development (TDD).

Comments

• Comments in code provide extra information to the reader and do no affect how code runs.
• Comments in Python start with #
• Do not overcomment — let you code speak clearly for itself.
• Also do not leave too much commented code in program to clean up later.

Not covered

Several things that usually show up in the beginner courses but you can survive without and catch up later:

• None,
• sets.

Several topics that do not show up often as but are quite useful, consider researching them:

• dataclasses,
• enums,
• working with dates and time,
• asc() and ord() for ASCII character code.

Short Glossary

• Boolean: A data type with two possible values: True or False.
• Condition: An expression that evaluates to a boolean value, used to control the flow of a program.
• Data type: A classification of data that tells the compiler or interpreter how to use the data.
• Expression: A combination of values, variables, operators, and functions that are evaluated to produce a new value.
• Function: A reusable block of code that performs a specific task.
• Loop: A code block that is repeated until a certain condition is reached.
• Variable: An identifier for a stored value that can be accessed or changed during program execution.