Summary: How to Write Reusable Code

OOP was not a silver bullet. How to write reusable code? Through hard work its not free or its magic. Required forethought and attention to detail. Caveat: Not everything needs to be library

Code Review arGreg Ward gave a great PyCon 2015 talk on how to make reusable code. We liked it, basically lays out 9 point guidelines that helps programmers make informed decisions about their design. Most of it might seem obvious but putting into use is where all the effort lies. Its a great investment of about 25mins of your time.

Overview

• OOP was not a silver bullet

• How to write reusable code?

  • Through hard work its not free or its magic.
  • Required foretought and attention to detail

• Caveat:

  • Not everything needs to be library

• Principles of Reusable Code:

  • Be a better programmer
  • Fewer classes, more functions
  • Funtions != procedures (beware of side effects)
  • Fewer frameworks, more libraries
  • Don’t go overboard
  • Don’t solve everything
  • Test, test, test
  • Document, document, document
  • Extensibility != reusability

Be a better programmer

• Read more code
• Write more code
• Read more books
• Do not learn to program from Google

• Book reccommendations:

  • The Practice of Programming
  • The Pragmatic Programmer
  • Beautiful Code
• Review and Refactor your code mercilessly

Fewer classes, more functions

• Don’t write classes when you need function
• A collection of related functions with shared state: that’s a class make one!

• Anti Pattern 1

  • a class with a single public method
  • especially a class with single method

• Anti Pattern 2

  • Opposite of Anti Pattern 1
  • If set of functions use same arguments and use similar data structure need to be in a Class

class ThingLoader:
    def __init__(self, host, id):
        self.host = host
        self.id = id

    def load(self):
        #
        #...

Functions != Procedures

• Pascal’s best idea: functions compute stuff, procedures do stuff
• mainstream imperative languages (C, Java, Python) don’t care
• You should care about distinction
• Rule of thumb: Every function should either return a value or have a side effect. Never both!

• Anti Pattern 1

  • C programmer are notorious for this sort of thing
  • Python programmers also do it
  • Compute and Modify original data-structure is bad

Fewer frameworks, more libraries

• Library: Code that you call (you are in control)
• Framework: Code that calls you (frameworks are in control)
• You can’t pick and choose which bits of framework you want
• It’s typically all or nothing
• This hampers reuse

Don’t go overboard

• OOP is a useful trick have in the toolbox
• Thus, calsses are not evil
• A computer is just a big box of numbers (with some wires going and some wires going out)
• Side effects are unavoidable: they are not evil
• Certain problem domains call out for constraints
• Frameworks are not evil

Don’t solve everything

• Avoid the temptation to handle every case: you will miss something
• Who can supply the functionality you left out? programmers, the very people who use your library
• Who can remove that bit of ill-advised code you put in that’s ruining my dat? NOBODY

Test, test, test

• Automated test are necessary but not sufficient
• Untested code is useless
• Tested code might be useful
• No controversy here: You must write tests

Document, document, document

• Documentation is necessary but not sufficient
• Undocumented code is useless
• Documented code might be useful
• Inline reference docs (docstring, java, etc) is bare minimum
• When you document every public method, you will find gaps
• This will also help write tests

Extensibility != Reusability

• Another part of the early 90s snake-oil promise: extensible, reusable software components
• Just because you type “class Foo” does not make your code reusable or extensible
• These are largely independent properties of software

Conclusion

• There is no such thing as free lunch
• Good stuff require efforts
• That includes reusable and/or extensible code
• Beware of pompous windbags, clueless pontifications and other purveyors of snake oil