Method, Class, Module, Package - how to they relate in Python?

A file containing a number of python methods and classes is known as a module. In the simplest of cases, it mighy just contain one class.

A directory containing a number of python modules is known as a package. In the simplest of cases, it may just contain one module.

Here's a sample program that loads a class (or two) from within a module from within a package:

  import bundle.thing

  iHave = bundle.thing.matchbox("catapillar")

  print(iHave)

In Python 2, you are required to mark a package as being a package by having a file called __init__.py in the directory. This was described as being necessary to avoic confusion between module names if your package contained modules of the same name as standard modules. Failure to provide the file results in:

  WomanWithCat:flask grahamellis$ python bundemo 

  Traceback (most recent call last):

    File "bundemo", line 2, in <module>

      import bundle.thing

  ImportError: No module named bundle.thing

  WomanWithCat:flask grahamellis$

In Python 3 there is no such requirement for a __init__.py file:

  WomanWithCat:flask grahamellis$ python3 bundemo 

  A Matchbox containing catapillar

  WomanWithCat:flask grahamellis$

Although not needed in Python 3, both versions support the file whichc also allows the specificiation of code to be run on load, and allows you to define a __all__ variable which controls what you load when you import or from *.

Files in this demo:
Demo program using package
Python module to go within package

(written 2015-10-17)

Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles

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  [2778] Learning to program in Python 2 ... and / or in Python 3 - (2010-05-24)
  [1696] Saying NOT in Perl, PHP, Python, Lua ... - (2008-07-04)
  [1661] Equality, sameness and identity - Python - (2008-05-31)
  [1477] Decisions - small ones, or big ones? - (2007-12-18)
  [1201] No switch in Python - (2007-05-23)
  [909] Python is like a narrowboat - (2006-10-30)
  [835] Python - when to use the in operator - (2006-08-16)
  [788] New - Conditional expressions in Python 2.5 - (2006-07-01)
  [668] Python - block insets help with documentation - (2006-04-04)
  [657] The ternary operator in Python - (2006-03-25)
  [353] Wimbledon Neck - (2005-06-20)
  [299] What - no switch or case statement? - (2005-05-03)

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Some other Articles

Clarrissa-Marybelle - too long to really fit?
Melksham - two small townships, or one big one?
RUH Hopper - experience and thoughts forward
Is the RUH hopper a limited, duplicate service running unnecessarily and at high cost?
Method, Class, Module, Package - how to they relate in Python?
RSpec - Ruby testing (stand alone example / no cucumber)
Saturday morning at Well House Manor
The principle of mocking - and the Python Mock package
Unittest of a Flask application including forms

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