Python Scope & Namespaces

 

Object

In general, anything that can be assigned to a variable in Python is referred to as an object.

Strings, Integers, Floats, Lists, Functions, Module etc. are all objects.

Identity of an Object

Whenever an object is created in Python, it will be given a unique identifier (id).This unique id can be different for each time you run the program.

Every object that you use in a Python Program will be stored in Computer Memory

The unique id will be related to the location where the object is stored in the Computer Memory.

Name of an Object

Name or Identifier is simply a name given to an object.

Namespaces

A namespace is a collection of currently defined names along with information about the object that the name references.

It ensures that names are unique and won’t lead to any conflict.

Namespaces allow us to have the same name referring different things in different namespaces.

Code

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def greet_1():

a = "Hello"

print(a)

print(id(a))

def greet_2():

a = "Hey"

print(a)

print(id(a))

print("Namespace - 1")

greet_1()

print("Namespace - 2")

greet_2()

PYTHON

Collapse

Output

Namespace - 1

Hello

140639382368176

Namespace - 2

Hey

140639382570608

Types of namespaces

As Python executes a program, it creates namespaces as necessary and forgets them when they are no longer needed.

Different namespaces are:

1. Built-in

2. Global

3. Local

Built-in Namespace

Created when we start executing a Python program and exists as long as the program is running.

This is the reason that built-in functions like id(), print() etc. are always available to us from any part of the program.

Global Namespace

This namespace includes all names defined directly in a module (outside of all functions).

It is created when the module is loaded, and it lasts until the program ends.

Local Namespace

Modules can have various

functions

and

classes

.

A new local namespace is created when a function is called, which lasts until the function returns.

Scope of a Name

The scope of a name is the region of a program in which that name has meaning.

Python searches for a name from the inside out, looking in the

local

,

global

, and

finally

the built-in namespaces.

Global variables

In Python, a variable defined outside of all functions is known as a global variable.

This variable name will be part of Global Namespace.

Example 1

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x = "Global Variable"

print(x)

def foo():

print(x)

foo()

PYTHON

Output

Global Variable

Global Variable

Example 2

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def foo():

print(x)

x = "Global Variable"

foo()

PYTHON

Output

Global Variable

Local Variables

In Python, a variable defined inside a function is a local variable.

This variable name will be part of the Local Namespace which will be created when the function is called and lasts until the function returns.

Code

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def foo():

x = "Local Variable"

print(x)

foo()

print(x)

PYTHON

Output

Local Variable

NameError: name 'x' is not defined

As,

x

is not declared before assignment, python throws an error.

Local Import

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def foo():

import math

print(math.pi)

foo()

print(math.pi)

PYTHON

Output

3.141592653589793

NameError: name 'math' is not defined

Local Variables & Global Variables

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x = "Global Variable"

def foo():

x = "Local Variable"

print(x)

print(x)

foo()

print(x)

PYTHON

Output

Global Variable

Local Variable

Global Variable

Modifying Global Variables

global

keyword is used to define a name to refer to the value in Global Namespace.

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x = "Global Variable"

def foo():

global x

x = "Global Change"

print(x)

print(x)

foo()

print(x)

PYTHON

Output

Global Variable

Global Change

Global Change