1. Python Modules

2. What are Python modules?
Files with previously written code that can be imported to the Python interpreter.
A module contains its own public and private variables to prevent interferences with user defined ones.
Modules file have .py extension

3. An example of a module $ vim modex.py def cube(x):
//Returns the value of x^3
return x*x*x,

4. Importing Modules >>> import modex >>> modex.cube(6)
216
>>> y = modex.cube(6)
>>>y

5. Accessing global variables in a module
Using dot notation.
>>> a = anymodule.globalvar
Note that a global variables will not affect another module; i.e. modify module1.gvar will not change the value of module2.gvar.

6. From/import statements
Used to import specific functions from a module
>>> from modex import cube
>>> cube(3)
>>>27

7. Executing modules as scripts
Python modules can be executed in command line whith
python modex.py <arguments>

8. Compiled Python files
When importing modex.py, a modex.pyc file is generated.
It contains the bytecode from the last time modex.py is imported.
If there is no .pyc file exists, it is created
For future imports, these .pyc files are used to speed up the loading time, not the execution time

9. The dir() function
This function returns a list of modules and functions that have been imported
>>> dir()
[‘_ _name_ _’, ‘_ _package_ _’]
>>>import modex
>>>dir()
[‘_ _name_ _’, ‘_ _package_ _’,’_ _modex’]

10. Standard Modules Python comes with a library of standard modules.
These modules contains built-in operations that are not actually part of Python’s core
Some of them are only imported based on the OS. For instance: winreg module is only provided on Windows systems.
An important Std module is sys. it is used to change the search path for the module
>>> sys.path.append(‘/home/pnp29/cs265_spring_2011

11. Packages They are organized collections of modules.
Modules are stored in directories
Each directory contains a __init__.py file which tells the Python interpreter that it is a package directory.

12. Example of a package math/ __init__.py triArea.py sqArea.py
statistics/
meanVal.py

13. Example of using packages
>>> import math.sqArea
>>> math.sqArea.area(5) 25
>>> from math.sqArea import area
>>> area(5)

14. Questions?

15. Sources