Variable.md

Variable

• Object Reference
  • Value has type, Variable do not has type

1. Define

• No Declaration Needed
• Define by assigning: <Var> = <Value>
• Life Cycle: Exist when needed, disapear when not needed

2. Scope

• Inside where defined: Module, Function, Class, Object
• Access
  • Access Global Variable in Local Scope:

global_variable = dummy_1

def fuction_1():
    global global_variable
    # Do something with global_variable

def fuction_2():
    global_variable = dummy_2
    # Wrong way: override global variable with same-name local variable

3. Copy

• Return a copy of current object: object.copy()

4. Annotation

• Annotation: A expression associated with the variable
  • Expression is evaluated when variable defined

<Variable>[: <Annotation>][ = <Value>]

4.1. Type Annotation

• Used for type hint and check

4.1.1. Generic Type

• Built-in Container Types cannot be used in Type Annotations to indicate its element's type

var: list[int]  # INVALID

• Use abstract base classes in typing module to support indicating element type of container type
  • Sequence: <ContainerType>[<ElementType>]
  • Dictionary: <Variable>: Dict[<KeyType>, <ValueType>]
  • Generic Container Type is defined with capitalization
    • E.g.: list (built-in) -> typing.List (Capitalized)

from typing import <ContainerType>

var: <ContainerType>[<ElementType>]  # VALID