It is more efficient to use if-return-return or if-else-return

Question

Suppose I have an if statement with a return  From the efficiency perspective  should I use  if A  gt  B       return A 1 return A-1   or  if A  gt  B       return A 1 else      return A-1   Should I prefer one or another when using a compiled language  C  or a scripted one  Python

User · Answer

I personally avoid else blocks when possible  See the Anti-if Campaign  Also  they don t charge  extra  for the line  you know  p    Simple is better than complex   amp   Readability is king   delta   1 if  A  gt  B  else -1 return A   delta

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Since the return statement terminates the execution of the current function  the two forms are equivalent  although the second one is arguably more readable than the first    The efficiency of both forms is comparable  the underlying machine code has to perform a jump if the if condition is false anyway   Note that Python supports a syntax that allows you to use only one return statement in your case   return A 1 if A  gt  B else A-1

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With any sensible compiler  you should observe no difference  they should be compiled to identical machine code as they re equivalent

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Version A is simpler and that s why I would use it   And if you turn on all compiler warnings in Java you will get a warning on the second Version because it is unnecesarry and turns up code complexity

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From Chromium s style guide   Don t use else after return     Bad if  foo    return 1 else   return 2    Good if  foo    return 1 return 2  return 1 if foo else 2

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Regarding coding style   Most coding standards no matter language ban multiple return statements from a single function as bad practice     Although personally I would say there are several cases where multiple return statements do make sense  text data protocol parsers  functions with extensive error handling etc   The consensus from all those industry coding standards is that the expression should be written as   int result   if A  gt  B      result   A 1    else     result   A-1    return result      Regarding efficiency   The above example and the two examples in the question are all completely equivalent in terms of efficiency  The machine code in all these cases have to compare A   B  then branch to either the A 1 or the A-1 calculation  then store the result of that in a CPU register or on the stack   EDIT    Sources    MISRA-C 2004 rule 14 7  which in turn cites     IEC 61508-3  Part 3  table B 9  IEC 61508-7  C 2 9

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This is a question of style  or preference  since the interpreter does not care  Personally I would try not to make the final statement of a function which returns a value at an indent level other than the function base   The else in example 1 obscures  if only slightly  where the end of the function is   By preference I use   return A 1 if  A  gt  B  else A-1   As it obeys both the good convention of having a single return statement as the last statement in the function  as already mentioned  and the good functional programming paradigm of avoiding imperative style intermediate results    For more complex functions I prefer to break the function into multiple sub-functions to avoid premature returns if possible  Otherwise I revert to using an imperative style variable called rval   I try not to use multiple return statements unless the function is trivial or the return statement before the end is as a result of an error   Returning prematurely highlights the fact that you cannot go on  For complex functions that are designed to branch off into multiple subfunctions I try to code them as case statements  driven by a dict for instance     Some posters have mentioned speed of operation  Speed of Run-time is secondary for me since if you need speed of execution  Python is not the best language to use  I use Python as its the efficiency of coding  i e  writing error free code  that matters to me

User · Answer

From a performance point of view  it doesn t matter in Python  and I d assume the same for every modern language out there  It really comes down to style and readability  Your second option  if-else block  is more readable than the first  and a lot more readable than the one-liner ternary operation

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I know the question is tagged python  but it mentions dynamic languages so thought I should mention that in ruby the if statement actually has a return type so you can do something like  def foo   rv   if  A  gt  B           A 1        else          A-1        end   return rv  end   Or because it also has implicit return simply   def foo    if  A gt B      A 1   else      A-1   end end   which gets around the style issue of not having multiple returns quite nicely

[python] It is more efficient to use if-return-return or if-else-return?

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