Python dictionary == operator

Its interesting to note that python dictionaries support the == operator

References:

• https://stackoverflow.com/a/5635309
• https://stackoverflow.com/questions/17217225/what-does-the-operator-actually-do-on-a-python-dictionary
• https://www.laurentluce.com/posts/python-dictionary-implementation/
  • This is a nice read on Python’s dictionary implementation using hash tables
• https://hg.python.org/cpython/file/6f535c725b27/Objects/dictobject.c#l1839

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Interfaces in Python : DuckTyping + ABCs

References:

• http://masnun.rocks/2017/04/15/interfaces-in-python-protocols-and-abcs/

Code:

 

Python sorted, itemgetter, stdin

I find it interesting how implementing a simple algorithm can teach you so many new things.

I was recently implementing the fractional knapsack problem

The interesting was – during implementation I got to learn some interesting things about Python.

• sorted
  • http://www.dr-chuck.com/csev-blog/2010/01/fun-python-syntax-operator-itemgetter-sorted-and-lambda-functions-oh-my/
  • https://algocoding.wordpress.com/2015/04/14/how-to-sort-a-list-of-tuples-in-python-3-4/
    • This link is actually quite useful!
• items, iteritems
  • https://stackoverflow.com/questions/10458437/what-is-the-difference-between-dict-items-and-dict-iteritems
• itemgetter
  • https://stackoverflow.com/questions/15371691/how-to-sort-a-dictionary-by-value-desc-then-by-key-asc
    • cool trick to sort by combination of ascending and descending
• sys.stdin
  • EOF literal for Windows is Control+Z  (not Control+D)

 

Code:

• fractional_knapsack.py

 

Python Break : Improve Your Python

I came across this very interesting series of blog posts. The authos (Jeff Knupp) discusses some nuances in Python

• Is Python call-by-value or call-by-reference? Neither.

• Improve Your Python: Python Classes and Object Oriented Programming

• Improve Your Python: Decorators Explained

 

There are a bunch of “Improve Your Python” articles in that blog. Check them out.

Code:

• python_scope.py

Python Class Attributes

I recently came across this interesting article on class attributes v/s instance attributes in Python.

References:

• https://www.toptal.com/python/python-class-attributes-an-overly-thorough-guide
  • This actually let me to 2 other guides which are very interesting:
  • https://pythonconquerstheuniverse.wordpress.com/2012/02/15/mutable-default-arguments/
  • https://timothyawiseman.wordpress.com/2012/10/06/class-and-instance-variables-in-python-2-7/
• http://www2.lib.uchicago.edu/keith/courses/python/class/5/##classinst
  • This is a very thorough guide. Highly recommended!

Code:

• _trail2.py

 

Factory Pattern in Python

I recently used the factory Pattern in Python.

• Gist

It was a little surprising to me comparing typical usage of this pattern in C# v/s Python.

In particular, in C# you’s typically have an Interface defining the methods and then provide an implementation of these methods in the concrete classes.

In Python, there is no interface – In the example above I embed a static  method in the base  to select the appropriate derived class.

Temp files in Python.

Recently, I hit a nasty bug while working with temp files in Python.

The issue was manifesting itself in Windows.  Interestingly I wasnt hitting it on Linux.

• As it so turns out I would have eventually hit it on Linux too.

 

The issue was because of a leaked file descriptor.  The following link explains the issue

• https://www.logilab.org/blogentry/17873