Python Namespace and Scope

What is Name in Python?

If you have ever read 'The Zen of Python' (type import this in the Python interpreter), the last line states, Namespaces are one honking great idea -- let's do more of those! So what are these mysterious namespaces? Let us first look at what name is.

Name (also called identifier) is simply a name given to objects. Everything in Python is an object. Name is a way to access the underlying object.

For example, when we do the assignment a = 2, 2 is an object stored in memory and a is the name we associate it with. We can get the address (in RAM) of some object through the built-in function id(). Let's look at how to use it.

# Note: You may get different values for the id

a = 2
print('id(2) =', id(2))

print('id(a) =', id(a))

Output

id(2) = 9302208
id(a) = 9302208

Here, both refer to the same object 2, so they have the same id(). Let's make things a little more interesting.

# Note: You may get different values for the id

a = 2
print('id(a) =', id(a))

a = a+1
print('id(a) =', id(a))

print('id(3) =', id(3))

b = 2
print('id(b) =', id(b))
print('id(2) =', id(2))

Output

id(a) = 9302208
id(a) = 9302240
id(3) = 9302240
id(b) = 9302208
id(2) = 9302208

What is happening in the above sequence of steps? Let's use a diagram to explain this:

Memory diagram of variables in Python

Initially, an object 2 is created and the name a is associated with it, when we do a = a+1, a new object 3 is created and now a is associated with this object.

Note that id(a) and id(3) have the same values.

Furthermore, when b = 2 is executed, the new name b gets associated with the previous object 2.

This is efficient as Python does not have to create a new duplicate object. This dynamic nature of name binding makes Python powerful; a name could refer to any type of object.

>>> a = 5
>>> a = 'Hello World!'
>>> a = [1,2,3]

All these are valid and a will refer to three different types of objects in different instances. Functions are objects too, so a name can refer to them as well.


def printHello():
    print("Hello")


a = printHello

a()





Output
Hello

The same name a can refer to a function and we can call the function using this name.


What is a Namespace in Python?

Now that we understand what names are, we can move on to the concept of namespaces.

To simply put it, a namespace is a collection of names.

In Python, you can imagine a namespace as a mapping of every name you have defined to corresponding objects.

Different namespaces can co-exist at a given time but are completely isolated.

A namespace containing all the built-in names is created when we start the Python interpreter and exists as long as the interpreter runs.

This is the reason that built-in functions like id(), print() etc. are always available to us from any part of the program. Each module creates its own global namespace.

These different namespaces are isolated. Hence, the same name that may exist in different modules do not collide.

Modules can have various functions and classes. A local namespace is created when a function is called, which has all the names defined in it. Similar, is the case with class. Following diagram may help to clarify this concept.