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Zen  of  Python  (PEP  20)

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>>>  import  this

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BeauLful  is  be"er  than  ugly

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Explicit  is  be"er  than  implicit

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Simple  is  be"er  than  complex

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Complex  is  be,er  than  complicated

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Flat  is  be"er  than  nested

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Sparse  is  be"er  than  dense

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Readability  Counts

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Special  cases  aren't  special  enough  to  break  the  rules.

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Although  pracLcality  beats  purity.

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Errors  should  never  pass  silently.

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Unless  explicitly  silenced.

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In  the  face  of  ambiguity,  refuse  the  tempta>on  to  guess.

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There  should  be  one-­‐-­‐  and  preferably  only  one  -­‐-­‐obvious  way  to  do  it.

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Although  that  way  may  not  be  obvious  at  first  unless  you're  Dutch.

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Dutch  Flag

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Now  is  be"er  than  never.

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Although  never  is  oFen  be,er  than  *right*  now.

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Why,  Eddie?

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If  the  implementa>on  is  hard  to  explain,  it's  a  bad  idea.

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If  the  implementa>on  is  easy  to  explain,  it  may  be  a  good  idea.

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Namespaces  are  one  honking  great  idea  -­‐-­‐  let's  do  more  of  those!

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PEP 8

Why a Style Guide matters.

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What  is  a  Style  Guide?

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SecLons

• Lay-­‐out• Imports• Whitespace• Comments• Document  Strings• Version  Bookkeeping• Naming  Conven>ons• Programming  Recommenda>ons

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Lay  Out

• 4  spaces– Unless  you’re  working  on  some  old  stuff  that  is  already  using  8  spaces

• Ver>cal  Alignment– Either  align  with  opening  delimiter– Or  use  extra  indenta>on

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Lay  Out

• Tabs  and  Spaces– Never  mix  the  two  (like  liquor  and  beer)– If  in  doubt,  go  with  spaces,  only.

• Maximum  Line  Length– 79  char.    – Use  the  implicit  line  wrap  within  parenthesis

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Lay  Out

• Blank  Lines– 2  lines  between  top  level  func>on  and  class  defini>on

– Use  blank  lines  to  logically  group  sec>ons– It’s  not  MLA.    Don’t  double-­‐space  your  code.  

• Encodings– Core  code  =  ASCII  or  La>n-­‐1– Code  >  3.0  should  use  UTF-­‐8

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Lay  Out

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Imports

• One  import  per  line• Put  at  the  top  of  the  document  aFer  comments  and  doc  strings– First  Standard  Library– Then  related  third-­‐party  imports– Last,  applica>on  /  library  specific  imports

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Whitespace

Too  much  is  too  much.

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Whitespace

• Don’t  get  cute  and  add  whitespace  within  parenthesis  or  brackets,  around  binary  operators.–Write  it  how  you  would  normally  write  it

• Do  use  spaces  around  arithme>c  operators–Math  is  hard  as  it  is,  don’t  make  it  harder  my  squishing  things  together...

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Whitespace  

• Don’t  put  compound  statements  on  one  line.• Spread  that  stuff  out  so  it  is  easy  to  find  the  various  clauses  and  stuff.

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Comments

• Comments  should  match  the  code.• If  there  is  a  conflict,  change  one  of  them!• Comments  should  be  complete  sentences,  wri,en  in  English.

• Lean  towards  using  block  comments.• Use  inline  comments  sparingly.• Don’t  be  the  obvious  troll.

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Doc  Strings

• Use  them!• PEP  257

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Naming  ConvenLons

• Single  Lower  (d)• Single  Upper  (W)• lowercase• lower_with_underscore• UPPERCASE• UPPER_WITH_UNDER• CamelCase• mixedCase

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Naming  ConvenLons  

• Avoid:– ‘l’,  ‘O’,  ‘I’

• Modules  should  be  short,  lowercase• Classes  in  CamelCase• Func>ons  should  be  lower_with_underscores• Constants  should  be  UPPER_WITH_UNDER

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Programming  RecommendaLons

• Thing  about  the  other  guys.• Don’t  use  equality  when  comparing  singletons• “if  X  is  not  None”  is  not  the  same  as  “if  X”

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