Introduction to Python Programming

• Python is a widely used, general-purpose, high-level programming language.
• Guido van Rossum initially designed Python in 1991.
• Python Software Foundation developed Python.
• Emphasis is placed on code readability.
• Python's syntax allows programmers to express concepts in fewer lines of code.
• The Python interpreter software reads source code and performs its instructions.
• Python 2.x and 3.x are the two most used versions.
• An interpreter executes other programs.
• Python programs convert source code into an intermediate language which is translated into native/machine code.
• Launching IDLE runs the interactive shell, which comes with the Python installation.
• The interactive shell is indicated by a window with the >>> prompt.
• Entering 2 + 2 at the prompt makes Python do simple math.
• In Python, 2 + 2 is an expression, which is the most basic kind of programming instruction.
• Expressions consist of values, such as 2, and operators, such as +.
• Expressions can always evaluate down to a single value.
• A single value with no operators is also considered an expression.
• Programs show an error message and crash if they contain code the computer cannot understand.
• Error messages do not break the computer, so mistakes are okay.
• A crash means the program stopped running unexpectedly.
• Searching for the exact message text online can help in finding out more about a specific error.
• There are other operators that you can use in Python expressions.

Math Operators in Python (Highest to Lowest Precedence)

• Exponent operator **: Example 2 ** 3 evaluates to 8.
• Modulus/remainder operator %: Example 22 % 8 evaluates to 6.
• Integer division/floored quotient operator //: Example 22 // 8 evaluates to 2.
• Division operator /: Example 22 / 8 evaluates to 2.75.
• Multiplication operator *: Example 3 * 5 evaluates to 15.
• Subtraction operator -: Example 5 - 2 evaluates to 3.
• Addition operator +: Example 2 + 2 evaluates to 4.
• The order of operations of Python math operators is similar to that of mathematics.
• The ** operator is evaluated first.
• The *, /, //, and % operators are evaluated next, from left to right.
• The + and - operators are evaluated last, also from left to right.
• Parentheses can be used to override the usual precedence.
• Example: (5 - 1) * ((7 + 1) / (3 - 1)) evaluates to 16.0.
• Rules for putting operators and values together to form expressions are a fundamental part of Python, just like grammar.
• If a line is difficult to parse because it doesn’t follow grammar rules, Python cannot understand it and displays a SyntaxError error message.
• If you don't follow proper operator precedence, Python evaluates your expression differently.
• Expressions are values combined with operators.
• Expressions always evaluate to a single value.
• Data type is a category for values.
• Every value belongs to exactly one data type.

Data Types and Examples

• Integers: -2, -1, 0, 1, 2, 3, 4, 5
• Floating-point numbers: -1.25, -1.0, 0.5, 0.0, 0.5, 1.0, 1.25
• Strings: 'a', 'aa', 'aaa', 'Hello', "pogi", '150 per kilo'
• Integer data types are whole numbers.
• Numbers with a decimal point are called floating-point numbers.
• 42.0 would be a floating-point number, but 42 is an integer.
• Python programs can also have text values called strings.
• Surround strings in single quote (') or double quotes (") characters.
• '' is a string with no characters in it, called a blank string.
• SyntaxError: EOL while scanning string literal means you probably forgot the final single quote character at the end of the string.
• The meaning of an operator may change based on data types.
• The + operator is addition for integers or floating-point values.
• When + is used on two string values, it joins the strings as the string concatenation operator.
• The + operator on a string and an integer value leads to an error message.
• The * operator is multiplication when it operates on two integer or floating-point values.
• The * operator is string replication when used on one string value and one integer value.
• A variable is like a box in the computer’s memory where you can store a single value.
• The result of an evaluated expression can be saved inside a variable.
• Assignment statements store values in variables.
• An assignment statement consists of a variable name, an equal sign (the assignment operator), and the value to be stored.
• A variable is initialized the first time a value is stored in it, and can be used in expressions with other variables and values after that.
• Assigning a variable a new value overwrites the old value.

Variable Name Rules

• Can be only one word.
• It can use only letters, numbers, and the underscore _ character.
• It can’t begin with a number.
• Variable names are case-sensitive.
• Spam, SPAM, Spam, and sPaM are four different variables.
• The interactive shell is good for running Python instructions one at a time.
• To write entire Python programs, type the instructions into the file editor.
• The file editor is similar to text editors such as Notepad, but it has specific features for typing in source code.
• The file editor lets you type in many instructions, save the file, and run the program.
• The interactive shell window will always be the one with the >>> prompt.
• The file editor window will not have the >>> prompt.
• Code is typed in the editor window.
• The interactive shell will display the output through the print command.