Python: Objects

Every object has a type

Every object has type. This type determines the abilities of an object and by extension what an object represents.

Because in Python a type is also an object, the type of a type is the type type.

The built-in function type(obj) returns the type-object of obj.

def printTypeOfType(obj):

    type_of_obj  = type(obj        )
    type_of_type = type(type_of_obj)

    print(f'obj          = {obj         }')
    print(f'type_of_obj  = {type_of_obj }')
    print(f'type_of_type = {type_of_type}')
    print('')

printTypeOfType( 42          )
#
# obj          = 42
# type_of_obj  = <class 'int'>
# type_of_type = <class 'type'>

printTypeOfType( 99.9        )
#
# obj          = 99.9
# type_of_obj  = <class 'float'>
# type_of_type = <class 'type'>

printTypeOfType('Hello world')
#
# obj          = Hello world
# type_of_obj  = <class 'str'>
# type_of_type = <class 'type'>

printTypeOfType(printTypeOfType)
#
# obj          = <function printTypeOfType at 0x000001F329B07F70>
# type_of_obj  = <class 'function'>
# type_of_type = <class 'type'>

Github repository about-Python, path: /objects/objects-have-a-type.py

Serialization (persistation)

Python objects might be serialized (persisted) with the pickle, shelve or json module.

Internal C structures and mechanisms

CPython stores a Python object internally in a PyObject or PyVarObject (if variable size) struct (both defined in Include/object.h)

All objects except type objects are always allocated on the heap, never on the stack.

The characteristics of a given type are stored in a PyTypeObject struct.

dir

If obj is an object that has a method named __dir__, this method will be called by dir(obj).

This is typically used in conjuction with __getattr__() and/or __getattribute__().

Python: Objects

Every object has a type

Serialization (persistation)

Mutable vs immutable objects

Internal C structures and mechanisms

dir

See also