2nd hardest thing in computer science

Definition?

There are only two hard things in Computer Science: cache invalidation and naming things.

Phil Karlton

There are 2 hard problems in computer science: cache invalidation, naming things, and off-by-1 errors

Leon Bambrick

There are only two hard problems in distributed systems:

2. Exactly-once delivery

1. Guaranteed order of messages

2. Exactly-once delivery

Mathias Verraes

#2 Naming things*

*things

• variables
• methods
• classes
• modules
• comments
• inline docs

You don't code for CPU

You don't code for interpreter

You don't code for compiler

You code for people

You code for other developers

You code for your future self

Don't code,

wrote prose

Always code as if the guy who ends up maintaining your code will be a violent psychopath who knows where you live.

Code for readability.

John F. Woods

Comprehension

~70%

def a(b):
    c = sorted(b)
    d = len(b)
    if d % 2 == 1:
        return c[(d - 1) / 2]
    else:
        return (c[d/2 - 1] + c[d/2]) / 2

def median(pool):
    copy = sorted(pool)
    size = len(copy)
    if size % 2 == 1:
        return copy[(size - 1) / 2]
    else:
        return (copy[size/2 - 1] + copy[size/2]) / 2

Self-documenting code

Code written by somebody else

Programming is mapping

• from problem domain
• via intermediate domain
• into programming domain

DDD FTW

Worst variable name

data

Second worst name?

data2

total = price * qty
total2 = total - discount
total2 += total * taxrate

total3 = purchase_order_value + available_credit
if total2 < total3:
  print ("You can't afford this order.")

order_total = price * qty
payable_total = order_total - discount
payable_total += payable_total * taxrate

available_funds = purchase_order_value + availble_credit
if payable_total < available_funds:
  print ("You can't afford this order.")

No-one sets out to write legacy code

Rachel Willmer

Broken window theory

Code will decay

Design patterns

Misapplied Java design ​patterns

are the root of all AbstractWordFactoryFactory("evil")

HN comment

PEP8

TL;DR

• CamelCaseClass
• method_with_underscores
• CAPITAL_CONSTANT

syntax < semanthics

Pseudo getter

get_data()

with extra operations inside

get_create_object()

• fetch
• find
• lookup
• create
• calculate

Not really a boolean

is_active()

def is_active():
  if cond:
    return 'false'
  return 'true'

is_valid()

def is_valid():
  if input_is_valid:
    return True

Plural / singular names

def get_person():
  return ['John Doe', 'Jane Doe']

def get_employers():
  return 'John Doe'

Misleading docs

def get_lowest_price(user):
  pass

def get_lowest_price(user):
  """Actually it returns the highest price."""
  pass

Doctest

def median(pool):
    '''Statistical median to demonstrate doctest.
    >>> median([2, 9, 9, 7, 9, 2, 4, 5, 8])
    7
    '''
    copy = sorted(pool)
    size = len(copy)
    if size % 2 == 1:
        return copy[(size - 1) / 2]
    else:
        return (copy[size/2 - 1] + copy[size/2]) / 2

if __name__ == '__main__':
    import doctest
    doctest.testmod()

<ThatThing>Manager

• UserManager
• StringManager
• ProductManager
• etc.

Alternatives

• Builder
• Writer
• Adapter
• Factory
• Handler
• Provider
• Converter

Magic numbers

import requests

response = requests.get('https://cz.pycon.org/2017/')
if response.status_code == 200:
  print ("It works!")
elif response.status_code == 418:
  print ("Unexpected teapot!")

import requests

response = requests.get('https://cz.pycon.org/2017/')
if response.status_code == requests.codes.ok:
  print ("It works!")
elif response.status_code == requests.codes.teapot:
  print ("Unexpected teapot!")

Useless comments

def get_data():
  """ Returns the data. """
  pass

def get_max_id_from_db():
  """ Return maximum ID value from the database."""
  pass

Explain why,

not what or how

Commit message

Good commit message

• Speed up review
• Help write release notes
• Help future maintainers

Short (50 chars or less) summary of changes

More detailed explanatory text, if necessary.  Wrap it to
about 72 characters or so.  In some contexts, the first
line is treated as the subject of an email and the rest of
the text as the body.  The blank line separating the
summary from the body is critical (unless you omit the body
entirely); tools like rebase can get confused if you run
the two together.

Further paragraphs come after blank lines.

  - Bullet points are okay, too

  - Typically a hyphen or asterisk is used for the bullet,
    preceded by a single space, with blank lines in
    between, but conventions vary here

Do not use negation

is_not_enabled()

How?

Agree on standards

Boy scout rule

Practice

Improve vocabulary

Refactor

Code reviews

Short, bite size, single logical change

Code ownership

Team leader's role

Links

• https://martinfowler.com/bliki/TwoHardThings.html
• https://www.python.org/dev/peps/pep-0008/
• https://groups.google.com/d/msg/comp.lang.c++/rYCO5yn4lXw/oITtSkZOtoUJ
• https://www.cqse.eu/publications/2005-concise-and-consistent-naming.pdf
• http://www.cs.loyola.edu/~lawrie/papers/lawrieJese07.pdf
• https://www.researchgate.net/publication/224079441_Relating_Identifier_Naming_Flaws_and_Code_Quality_An_Empirical_Study
• http://www.veneraarnaoudova.com/wp-content/uploads/2014/10/2014-EMSE-Arnaodova-et-al-Perception-LAs.pdf​
• http://archive.oreilly.com/pub/post/the_worlds_two_worst_variable.html
• https://twitter.com/amokleben/status/868377283496751104?s=09
• https://twitter.com/tmmx/status/865308678903267328
• https://wiki.python.org/moin/SimplePrograms

Thank you!

@pawel_lewtak