Python 101 · Data Types and Behaviors

Jan 2, 2016 | Tech Software

Index

Index

Data Types

All data types in Python are objects and are passed by object reference.
Variables are essentially labels for objects; "modifying" immutable types actually makes a label point to a new address.

Type	Name	Mutability	Behavior
Integer	`int`	Immutable	Modification: creates new object, similar to Value Copy effect
Float	`float`	Immutable	Modification: same as above
String	`str`	Immutable	Modification: same as above
Boolean	`bool`	Immutable	Modification: same as above, `bool` inherits from `int`
Tuple	`tuple`	Immutable	Modification: cannot be modified in place Empty instance: `tuple()` or `()`
List	`list`	Mutable	Modification: in-place modification, affects all references Empty instance: `list()` or `[]`
Dictionary	`dict`	Mutable	Modification: same as above Empty instance: `dict()` or `{}`
Set	`set`	Mutable	Modification: same as above Empty instance: `set()`
Custom Class	`class`	Mutable by default	Modification: in-place attribute modification Empty instance: `Foo(bar, ...)`, constructor dependent

Common Container Methods

tuple
: immutable, ordered, allows duplicate items.

list
: mutable, ordered, allows duplicate items.

dict
: mutable, unordered, forbids duplicate keys.

set
: mutable, unordered, forbids duplicate items.

Common Container Functions
:
- len(), min(), max(), sum(), and
- typical Iterator methods shown in Python 101 · Iterators, Generators, Comprehensions, Iterable, Hashable.

Common String Methods

join, split, find, replace, count;
upper, lower, title, capitalize, etc.

Indexing and Slicing

works for sequence types such as strings, lists, tuples, etc

F-String

preferred over str.format() since Python 3.6

Object Reference & "Labels" to New Addresses

Functions "Modifying" Immutable Inputs

Immutable Custom Classes

Duck Typing

A programming concept where an object's suitability is determined by the presence of certain methods and properties, rather than its actual type or inheritance.
"If it walks like a duck and quacks like a duck, then it must be a duck." — James Whitcomb Riley

Type Casting, Hints, Checks

Implicit by Design
: Python follows the Duck Typing principle and performs implicit type inference and conversions, but sometimes it can be helpful to explicity suggest or specify types.

Typecasting
: The explicit process of converting a value from one data type to another, which triggers immediate validation and raises an error if the conversion is logically impossible.

Type Hints
: A formal annotation system used to specify the expected data types of variables, function parameters, and return values to improve code clarity and enable static analysis without affecting runtime behavior.

Type Checks (Manual, Automated)
: The process of verifying that a program adheres to type constraints, which can occur statically (before execution) via IDE or dynamically (at runtime) via logic or modules, such as isinstance(), @typechecked, pydantic, or numpy with type specifiers, to ensure data integrity.