Python Modules

Python Modules

A module allows you to logically organize your Python code. Grouping related code into a module makes the code easier to understand and use. A module is a Python object with arbitrarily named attributes that you can bind and reference.

Simply, a module is a file consisting of Python code. A module can define functions, classes and variables. A module can also include runnable code.

The import Statement

You can use any Python source file as a module by executing an import statement in some other Python source file. The import has the following syntax

import module1[, module2[,... moduleN]

When the interpreter encounters an import statement, it imports the module if the module is present in the search path. A search path is a list of directories that the interpreter searches before importing a module. For example, to import the module support.py, you need to put the following command at the top of the script

# Import module support
import support

# Now you can call defined function that module as follows
support.print_func("drk")

Hello : drk

A module is loaded only once, regardless of the number of times it is imported. This prevents the module execution from happening over and over again if multiple imports occur.

The from…import Statement

Python’s from statement lets you import specific attributes from a module into the current namespace. The from…import has the following syntax

from modname import name1[, name2[, ... nameN]]

For example, to import the function fibonacci from the module fib, use the following statement −

from fib import fibonacci

This statement does not import the entire module fib into the current namespace; it just introduces the item fibonacci from the module fib into the global symbol table of the importing module.

The from…import * Statement

It is also possible to import all names from a module into the current namespace by using the following import statement

from modname import *

This provides an easy way to import all the items from a module into the current namespace; however, this statement should be used sparingly.

Locating Modules

When you import a module, the Python interpreter searches for the module in the following sequences −

• The current directory.
• If the module isn’t found, Python then searches each directory in the shell variable PYTHONPATH.
• If all else fails, Python checks the default path. On UNIX, this default path is normally /usr/local/lib/python/.

The module search path is stored in the system module sys as the sys.path variable. The sys.path variable contains the current directory, PYTHONPATH, and the installation-dependent default.

Python Packages

A package is a hierarchical file directory structure that defines a single Python application environment that consists of modules and subpackages and sub-subpackages, and so on.

Consider a file Pots.py available in Phone directory. This file has following line of source code −

def Pots():
   print "I'm Pots Phone"

Similar way, we have another two files having different functions with the same name as above −

• Phone/Isdn.py file having function Isdn()
• Phone/G3.py file having function G3()
• Now, create one more file init.py in Phone directory

To make all of your functions available when you’ve imported Phone, you need to put explicit import statements in init.py as follows

from Pots import Pots
from Isdn import Isdn
from G3 import G3

After you add these lines to init.py, you have all of these classes available when you import the Phone package.

# Now import your Phone Package.
import Phone as p

p.Pots()

I'm a Pots Phone.

p.Isdn()

I'm an Isdn phone.

p.G3()

I'm a G3 phone.