Are one-line if for -statements good Python style

Question

Every so often on here I see someone s code and what looks to be a  one-liner   that being a one line statement that performs in the standard way a traditional  if  statement or  for  loop works   I ve googled around and can t really find what kind of ones you can perform  Can anyone advise and preferably give some examples   For example  could I do this in one line   example    example  if  exam  in example      print  yes     Or   for a in someList      list append splitColon split a

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for a in someList      list append splitColon split a     You can rewrite the above as   newlist    splitColon split a  for a in someList

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More generally  all of the following are valid syntactically   if condition      do something     if condition  do something    if condition      do something       do something else    if condition  do something    do something else        etc

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I ve found that in the majority of cases doing block clauses on one line is a bad idea   It will  again as a generality  reduce the quality of the form of the code   High quality code form is a key language feature for python   In some cases python will offer ways todo things on one line that are definitely more pythonic  Things such as what Nick D mentioned with the list comprehension    newlist    splitColon split a  for a in someList    although unless you need a reusable list specifically you may want to consider using a generator instead  listgen    splitColon split a  for a in someList    note the biggest difference between the two is that you can t reiterate over a generator  but it is more efficient to use    There is also a built in ternary operator in modern versions of python that allow you to do things like  string to print    yes   if  exam  in  example  else    print string to print   or   iterator   max value if iterator  gt  max value else iterator   Some people may find these more readable and usable than the similar if  condition   block   When it comes down to it  it s about code style and what s the standard with the team you re working on   That s the most important  but in general  i d advise against one line blocks as the form of the code in python is so very important

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You could do all of that in one line by omitting the example variable   if  exam  in  example   print  yes

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Dive into python has a bit where he talks about what he calls the and-or trick  which seems like an effective way to cram complex logic into a single line   Basically  it simulates the ternary operater in c  by giving you a way to test for truth and return a value based on that  For example    gt  gt  gt   1 and   firstvalue   or   secondvalue    0   firstvalue   gt  gt  gt   0 and   firstvalue   or   secondvalue    0   secondvalue

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Well   if  exam  in  example   print  yes     Is this an improvement  No  You could even add more statements to the body of the if-clause by separating them with a semicolon  I recommend against that though

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Older versions of Python would only allow a single simple statement after for      if      or similar block introductory statements   I see that one can have multiple simple statements on the same line as any of these   However  there are various combinations that don t work   For example we can   for i in range 3   print  Here s i    print i       but  on the other hand  we can t   for i in range 3   if i   2  print  That s odd     We can   x 10 while x  gt  0  print x  x- 1       but we can t   x 10  while x  gt  0  print x  x- 1       and so on   In any event all of these are considered to be extremely NON-pythonic   If you write code like this then experience Pythonistas will probably take a dim view of your skills   It s marginally acceptable to combine multiple statements on a line in some cases   For example   x 0  y 1       or even   if some condition    break       for simple break continue and even return statements or assigments   In particular if one needs to use a series of elif one might use something like   if     keystroke     q     break elif   keystroke     c     action  continue  elif   keystroke     d     action  delete        else                       action  ask again        then you might not irk your colleagues too much    However  chains of elif like that scream to be refactored into a dispatch table     a dictionary that might look more like   dispatch          q   foo break       c   foo continue       d   foo delete               while True      key   SomeGetKey       dispatch get key  foo try again

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Python lets you put the indented clause on the same line if it s only one line   if  exam  in example  print  yes    def squared x   return x   x  class MyException Exception   pass

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an example of a language feature that isn t just removing line breaks  although still not convinced this is clearer than the more verbose version     a   1 if x   15 else 2

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This is an example of  if else  with actions    gt  gt  gt  def fun num       print  This is  d    num  gt  gt  gt  fun 10  if 10  gt  0 else fun 2  this is 10 OR  gt  gt  gt  fun 10  if 10  lt  0 else 1 1

[python] Are one-line 'if'/'for'-statements good Python style?

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