450738551-Modules-and-Packages-in-python-1-ppt.ppt

450738551-Modules-and-Packages-in-python-1-ppt.ppt

• 2.
  What are Modules? Modules are files containing Python definitions and statements (ex. name.py)  A module’s definitions can be imported into other modules by using “import name”  The module’s name is available as a global variable value  To access a module’s functions, type “name.function()”
• 3.
  Modules…  A moduleallows 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.
• 4.
  Program using Module The Python code for a module named printfunction normally resides in a file named printfunction.py.  Here's an example of a simple module, printfunction.py def print_func( param ): print ("Hello : ", param) return
• 5.
  More on Modules Modules can contain executable statements along with function definitions  Each module has its own private symbol table used as the global symbol table by all functions in the module  Modules can import other modules  Each module is imported once per interpreter session  reload(name)  Can import names from a module into the importing module’s symbol table  from mod import m1, m2 (or *)  m1()
• 6.
  From…import statement  Python'sfrom 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.
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  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 *
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  Executing Modules  pythonname.py <arguments>  Runs code as if it was imported  Setting _name_ == “_main_” the file can be used as a script and an importable module
• 9.
  The Module SearchPath  The interpreter searches for a file named name.py  Current directory given by variable sys.path  List of directories specified by PYTHONPATH  Default path (in UNIX - .:/usr/local/lib/python)  Script being run should not have the same name as a standard module or an error will occur when the module is imported
• 10.
  “Compiled” Python Files If files mod.pyc and mod.py are in the same directory, there is a byte-compiled version of the module mod  The modification time of the version of mod.py used to create mod.pyc is stored in mod.pyc  Normally, the user does not need to do anything to create the .pyc file  A compiled .py file is written to the .pyc  No error for failed attempt, .pyc is recognized as invalid  Contents of the .pyc can be shared by different machines
• 11.
  Standard Modules  Pythoncomes with a library of standard modules described in the Python Library Reference  Some are built into interpreter  >>> import sys >>> sys.s1 ‘>>> ‘ >>> sys.s1 = ‘c> ‘ c> print ‘Hello’ Hello c>  sys.path determines the interpreters’s search path for modules, with the default path taken from PYTHONPATH  Can be modified with append() (ex. Sys.path.append(‘SOMEPATH’)
• 12.
  The dir() Function Used to find the names a module defines and returns a sorted list of strings  >>> import mod >>> dir(mod) [‘_name_’, ‘m1’, ‘m2’]  Without arguments, it lists the names currently defined (variables, modules, functions, etc)  Does not list names of built-in functions and variables  Use _bulltin_to view all built-in functions and variables
• 13.
  Packages  “dotted modulenames” (ex. a.b)  Submodule b in package a  Saves authors of multi-module packages from worrying about each other’s module names  Python searches through sys.path directories for the package subdirectory  Users of the package can import individual modules from the package  Ways to import submodules  import sound.effects.echo  from sound.effects import echo  Submodules must be referenced by full name  An ImportError exception is raised when the package cannot be found
• 14.
  Importing * Froma Package  * does not import all submodules from a package  Ensures that the package has been imported, only importing the names of the submodules defined in the package  import sound.effects.echo import sound.effects.surround from sound.effects import *
• 15.
  Intra-package References  Submodulescan refer to each other  Surround might use echo module  import echo also loads surround module  import statement first looks in the containing package before looking in the standard module search path  Absolute imports refer to submodules of sibling packages  sound.filters.vocoder uses echo module from sound.effects import echo  Can write explicit relative imports  from . import echo  from .. import formats  from ..filters import equalizer
• 16.
  Packages in Multiple Directories _path_ is a list containing the name of the directory holding the package’s _init_.py  Changing this variable can affect futute searches for modules and subpackages in the package  Can be used to extend the set of modules in a package  Not often needed
• 17.
  Sources  http://docs.python.org/tutorial/modules.html