6. Namespace and scoping rules

Only 3 namespaces are visible to the developer: local, global, built-in.

You can obtain the loca namespace with:

locals()

and the global one with:

globals()

There are 2 dictionaries so you can get the key/value pairs.

Todo

this section will present namespace and scopes

local namespace

parameter names local variable names

global namespace (module-level)

function names class names import modules names variable names global variables names in functions

built-in namespace (predefined names). built-in function names: len, str built-in exception names (TypeError)

Let us consider a function with only one local variable:

>>> def A(b):
...    x=1
...    print locals()
>>> A()
{'x': 1, 'b': 1}

The vars() return a dictionary corresponding to the local namespace of an object (e.g., a module):

import math
vars(math)

Without an object, vars() returns the same as locals().

To get the built-in namespace, type

dir(__builtin__)

to obtain a sorted list of names in the built-in namespace and

vars(__builtin__)

to obtain the dictionary correspondinf to the built-in namespace.

See global variable for an example using a function.

6.1. nested functions

Since python 2.1, nested scopes are available, which means that python searches for variables in the function’s namespace, then in the parent’s function namespace, and finally in the module’s namespace

c = 1
def func1(a, b):

    def inner_func(x):
        return x*x*x + c

    return inner_func(a) + inner_func(b)

is valid code, c=1 will be used within the inner function.