Variables, Data Types, and Operators

Variables, Data Types, and Operators

Review lesson. A summary table of the variables, data types, and operators part of Module 1, for quick lookup and self-checking after studying units 1.2 → 1.6. If anything is still unclear, go back to the corresponding unit and rewatch the video.

Data types

Type	Example	Ordered	Mutable	Notes
int, float	42, 3.14	—	—	/ always gives a float, // is floor division
str	'Python'	Yes	No	Indexing starts at 0, slice s[a:b] stops before b
bool	True, False	—	—	True + True equals 2
list	[1, 2, 3]	Yes	Yes	b = a does not copy; use a.copy()
tuple	(1, 2)	Yes	No	A single element needs a comma: (50,)
set	{1, 2, 3}	No	Yes	Duplicate elements are not allowed
dict	{"a": 1}	Yes	Yes	Keys are unique; d.get(k, default) does not raise an error when the key is missing

Operators and precedence

From highest to lowest: ** → * / % // → + - → comparison → is, in → not and or.

Four easily confused points

• input() always returns a string; to do arithmetic you must convert the type: int(input(...)).
• == compares values, is checks for the same object (commonly used for None).
• Falsy values: False None 0 0.0 '' [] () {} set(); the string "False" is still truthy.
• int(3.99) is 3 — int() truncates the decimal part, it does not round.

Key points

• Variables/functions use snake_case, constants use UPPER_SNAKE_CASE, classes use PascalCase.
• Mutable types (list, set, dict) and immutable types (str, tuple) determine how they behave when assigned and passed into functions.