What are Python namespaces all about

Question

I have just started learning Python & have come across "namespaces" concept in Python. While I got the jist of what it is, but am unable to appreciate the gravity of this concept.

Some browsing on the net revealed that one of the reasons going against PHP is that it has no native support for namespaces.

Could someone explain how to use namespaces & how this feature makes programming better (not just in Python, as I assume namespaces in not a concept limited to a particular language).

I am predominantly coming from Java and C programming backgrounds.

user_7131757 · Answer

Namespaces provide a way for managing identifiers defined within a scope. In other words, they are used to map names to values (or references to the memory location to be more precise).

For example, in the context of a namespace the following expression

x = 10

will associate identifier x to the memory location that holds object with value 10.

In Python, there are essentially two "types" of namespaces; instance and class namespaces.

Instance Namespace manages the mapping between names and values within the scope of a individual object. On the other hand, there is a separate Class Namespace for every class defined in the source code. This type of namespace handles all the members which are shared by all instances of the object.

Example

Now consider the following example where for each member it is denoted whether it belongs to a class or instance namespace:

class Customer:

    def __init__(self, first_name, last_name, email): # __init__ -> Customer Class Namespace
        self._first_name = first_name # _first_name -> Instance Namespace
        self._last_name = last_name # _last_name -> Instance Namespace
        self._email = email # _email -> Instance Namespace

    def get_full_name(self): # Customer Class Namespace
        return f"{self._first_name} {self._last_name}"


class PremiumCustomer(Customer):

    PREMIUM_MEMBERSHIP_COST = 4.99  # PremiumCustomer Class Namespace


    class Subscription: # PremiumCustomer Class Namespace

        def __init__(self, customer_email): # Subscription Class Namespace
            self._customer_email = customer_email # Instance Namespace

    def __init__(self, first_name, last_name, email, card_number): # PremiumCustomer Class Namespace
        super().__init__(first_name, last_name, email)
        self._card_number = card_number # _card_number -> Instance Namespace

    def get_card_number(self): # PremiumCustomer Class Namespace
        return self._card_number

user_1419272 · Answer

I complete the answer of S.Lott.

I would say, namespace is a way to implement name management inside a scope, because a scope does more than name management.

In C the scopes are of 4 types: global, function, block and function-parameters(prototype). Each of these kinds can create one or more namespaces, depending on the needs. There are 4 ns in C -- tags for s/u/e -- ids for typenames, function names and var names -- parameters inside function prototype -- members and bitfields inside s/u.

Like that, tag identifiers and function names do not collide, but typenames defined by typedef can collide with variable names.

In python there is a builtin namespace that encloses the global ns, and the global ns is provided by the loaded module. The builtin ns contain variables. A symbol for a variable can define an object or a function -- for example, + is defined there. The module's global ns lasts up to the termination.

What are Python namespaces all about

6 Answers