Examples about using the name variable

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May 10, 2010 11:57:10 AM PDT (3 years ago). Seen 3,886 times. One reply.

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Ismail Ceylan

FQA Engineer

Financial Engines

Member since Apr 28, 2010
Forum Posts: 2

Every Python module includes a set of magic variables which can be seen by using the dir() function after importing the module. One of these magic variables, "__name__", stores either the name of that module or the string value "__main__". If the module is being run by itself than we have __name__ = '__main__'. However, whenever the module is imported from another location than the magic variable __name__ stores the name of that module. This can be confirmed by running the print command on the variable:

Code:

>>>print __name__
__main__

Code:

>>>import math
>>>print math.__name__
math

This property is very useful while writing and testing modules that could potentially be imported. The following piece of code is taken from the Marakana Python Training. It demonstrates how this magic variable can be used to test a module you wrote in a way that is not seen from outside of the code:

Code:

#!/usr/bin/env python
"""Unwraps and prints out a 2-D sequence.
Note that the testing only happens when this module
is the "__main__" module.
"""
def PrintTable(table):
    """Prints out a 2-D sequence"""
    for row in table:
        for column in row:
            print column,
        print
    print

def Test():
    tests = (["Hi", "Hola"], 
             (('H','i'), ('H','o','l','a')), 
             [["Hi"], ["Hola"]]
             )
    for test in tests:
        print test
        PrintTable(test)

if __name__ == '__main__':
    Test()
"""
$ tables.py
['Hi', 'Hola']
H i
H o l a

(('H', 'i'), ('H', 'o', 'l', 'a'))
H i
H o l a

[['Hi'], ['Hola']]
Hi
Hola

$ """

The line "if __name__ == '__main__':" checks if we are running this module by itself or importing it. The condition within the if statement evaluates to 'True' if we run the module by itself and the test code given in the function Test() is run. This is demontrated below by running this code in the interpreter:

Code:

['Hi', 'Hola']
H i
H o l a

(('H', 'i'), ('H', 'o', 'l', 'a'))
H i
H o l a

[['Hi'], ['Hola']]
Hi
Hola

However, when the module is imported, the condition evaluates to 'False' and the module is imported without any of the test code being run:

Code:

>>>import tables
>>>

Edited one time. Last edit by Ismail Ceylan on Jun 13, 2010 at 11:17:35 PM (about 2 years ago).

January 17, 2013 3:59:58 AM PST (21 weeks ago)

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Shivani Batra

Goldstonems

Member since Jan 11, 2013
Forum Posts: 7

Code:

def namestr(obj, namespace):
    return [name for name in namespace if namespace[name] is obj]

Edited 2 times. Last edit by Shivani Batra on Jan 17, 2013 at 4:01:09 AM (about 2 years ago).

Examples about using the __name__ variable

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