Download Python Modules

PYTHON MODULES
Modules in a Nutshell



Modules are text files you can import to the Python
interpreter in order to reuse previously written
code.
A module has its own global and local scopes to
prevent interference with user defined names.
A package is a collection of modules, grouped for
organization and easy access.
Module Example
$ vim mymodule.py
# a simple module
def square(x):
“””
Returns the square of its parameter.
“””
return x * x
Using a module
>>> import mymodule
>>> y = mymodule.square(2)
>>>y
4
>>>mymodule.square(y)
16
Call by Value
>>>
>>>
>>>
49
>>>
7
import mymodule
x=7
mymodule.square(x)
x
Accessing the module variables

You can access the global variables of a module
using dot notation.
>>> x = somemodule.somevariable

Global variables in a module will not otherwise
effect another module, or user defined components.
from/import Statements
You can import specific names from a module with a
from/import statement.
>>> from mymodule import square
>>> square(3)
9
>>> from mymodule import square, cube
>>> cube(2)
8
>>> from mymodule import *

The Importance of Returning
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Python modules don’t really handle function calls by
reference. Programmers have to work around this
with return statements.
>>> x = 2
>>> x = mymodule.square(2)
>>> x
4
Modules as Scripts
$ vim mymodule.py
def square(x):
print x * x
if __name__ == "__main__":
import sys
square(int(sys.argv[1]))
~
~
$ python mymodule.py 2
4
.pyc Files
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

On a successful import, a modulename.pyc file is
generated. This file contains the bytecode from the
last time the modulename.py file was imported.
The interpreter checks the date modified before
using the .pyc file, there is no danger of using an
older version.
These files only speed up the loading of a module,
not the execution.
dir()

dir() is useful for checking what modules you’ve imported.
>>> dir()
['__builtins__', '__doc__', '__name__', '__package__']
>>> import mymodule
>>> from mymodule import square
>>> dir()
['__builtins__', '__doc__', '__name__', '__package__', 'mymodule', 'square']
Standard Modules
import first checks the current directory for the
specified module.
 The interpreter then follows a default path like
/usr/local/lib/python, or the PYTHONPATH EV.
 To change the path, import “sys”, one of Python’s
standard modules.
>>> import sys
>>> sys.path.append(‘/home/jm4564/cs_265’)

A Package Example
math/
__init__.py
logarithms.py
circles.py
statistics/
factorial.py
…
…
Importing Packages
Packages can be imported in as large, or as small,
portions as you require.
>>> import math.circles
>>> math.circles.area(5)
78.53981634
>>> from math.circles import area
>>> area(3)
28.27433388
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Questions?
Source
Python v2.6.4 documentation >> The Python
Tutorial >> Modules
http://docs.python.org/tutorial/modules.html
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