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.
Python - Modules

The Python code for a module named aname
normally resides in a file named aname.py.
Here's an example of a simple module, support.py
Example
def print_func( par ):
print "Hello : ", par
return

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
The import Statement

#!/usr/bin/python
# Import module support
import support
# Now you can call defined function that module as
follows
support.print_func("Zara")
When the above code is executed, it produces the
following result
Hello : Zara
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.

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.

The PYTHONPATH Variable
The PYTHONPATH is an environment variable,
consisting of a list of directories.
The syntax of PYTHONPATH is the same as that of
the shell variable PATH.
Here is a typical PYTHONPATH from a Windows
system
set PYTHONPATH = c:python20lib;
And here is a typical PYTHONPATH from a UNIX
system
set PYTHONPATH = /usr/local/lib/python

Packages in Python
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
#!/usr/bin/python
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
Phone/__init__.py
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.
When the above code is executed, it produces the
following result
#!/usr/bin/python
# Now import your Phone Package.
import Phone
Phone.Pots()
Phone.Isdn()
Phone.G3()
I'm Pots Phone
I'm 3G Phone
I'm ISDN Phone

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