Python idiom to return first item or None

Question

I m sure there s a simpler way of doing this that s just not occurring to me   I m calling a bunch of methods that return a list   The list may be empty   If the list is non-empty  I want to return the first item  otherwise  I want to return None   This code works   my list   get list   if len my list   gt  0  return my list 0  return None   It seems to me that there should be a simple one-line idiom for doing this  but for the life of me I can t think of it   Is there   Edit   The reason that I m looking for a one-line expression here is not that I like incredibly terse code  but because I m having to write a lot of code like this   x   get first list   if x        do something with x 0        inevitably forget the  0  part  and have a bug to fix y   get second list   if y        do something with y 0        inevitably forget the  0  part AGAIN  and have another bug to fix   What I d like to be doing can certainly be accomplished with a function  and probably will be    def first item list or none       if list or none  return list or none 0   x   first item get first list    if x        do something with x y   first item get second list    if y        do something with y   I posted the question because I m frequently surprised by what simple expressions in Python can do  and I thought that writing a function was a silly thing to do if there was a simple expression could do the trick   But seeing these answers  it seems like a function is the simple solution

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Not sure how pythonic this is but until there is a first function in the library I include this in the source:

first = lambda l, default=None: next(iter(l or []), default)

It's just one line (conforms to black) and avoids dependencies.

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My use case was only to set the value of a local variable   Personally I found the try and except style cleaner to read  items    10  20  try  first item   items 0  except IndexError  first item   None print first item   than slicing a list   items    10  20  first item    items  1  or  None     0  print first item

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Using the and-or trick   a   get list   return a and a 0  or None

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You could use Extract Method  In other words extract that code into a method which you d then call   I wouldn t try to compress it much more  the one liners seem harder to read than the verbose version  And if you use Extract Method  it s a one liner

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Several people have suggested doing something like this   list   get list   return list and list 0  or None   That works in many cases  but it will only work if list 0  is not equal to 0  False  or an empty string   If list 0  is 0  False  or an empty string  the method will incorrectly return None           I ve created this bug in my own code one too many times

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for item in get list        return item

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You could use Extract Method  In other words extract that code into a method which you d then call   I wouldn t try to compress it much more  the one liners seem harder to read than the verbose version  And if you use Extract Method  it s a one liner

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If you find yourself trying to pluck the first thing  or None  from a list comprehension you can switch to a generator to do it like   next  x for x in blah if cond   None    Pro  works if blah isn t indexable Con  it s unfamiliar syntax  It s useful while hacking around and filtering stuff in ipython though

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If you find yourself trying to pluck the first thing  or None  from a list comprehension you can switch to a generator to do it like   next  x for x in blah if cond   None    Pro  works if blah isn t indexable Con  it s unfamiliar syntax  It s useful while hacking around and filtering stuff in ipython though

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Python 2 6   next iter your list   None    If your list can be None   next iter your list or      None    Python 2 4  def get first iterable  default None       if iterable          for item in iterable              return item     return default   Example   x   get first get first list    if x          y   get first get second list    if y            Another option is to inline the above function   for x in get first list   or           process x     break   process at most one item for y in get second list   or           process y     break   To avoid break you could write   for x in yield first get first list         x   process x for y in yield first get second list         y   process y   Where   def yield first iterable       for item in iterable or             yield item         return

User · Answer

get list   or  None   0    That should work   BTW I didn t use the variable list  because that overwrites the builtin list   function   Edit   I had a slightly simpler  but wrong version here earlier

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isn t the idiomatic python equivalent to C-style ternary operators   cond and true expr or false expr   ie    list   get list   return list and list 0  or None

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Python 2 6   next iter your list   None    If your list can be None   next iter your list or      None    Python 2 4  def get first iterable  default None       if iterable          for item in iterable              return item     return default   Example   x   get first get first list    if x          y   get first get second list    if y            Another option is to inline the above function   for x in get first list   or           process x     break   process at most one item for y in get second list   or           process y     break   To avoid break you could write   for x in yield first get first list         x   process x for y in yield first get second list         y   process y   Where   def yield first iterable       for item in iterable or             yield item         return

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The OP s solution is nearly there  there are just a few things to make it more Pythonic   For one  there s no need to get the length of the list  Empty lists in Python evaluate to False in an if check  Just simply say  if list    Additionally  it s a very Bad Idea to assign to variables that overlap with reserved words   list  is a reserved word in Python   So let s change that to  some list   get list   if some list    A really important point that a lot of solutions here miss is that all Python functions methods return None by default  Try the following below   def does nothing        pass  foo   does nothing   print foo   Unless you need to return None to terminate a function early  it s unnecessary to explicitly return None  Quite succinctly  just return the first entry  should it exist   some list   get list   if some list      return list 0    And finally  perhaps this was implied  but just to be explicit  because explicit is better than implicit   you should not have your function get the list from another function  just pass it in as a parameter  So  the final result would be  def get first item some list        if some list          return list 0   my list   get list   first item   get first item my list    As I said  the OP was nearly there  and just a few touches give it the Python flavor you re looking for

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Several people have suggested doing something like this   list   get list   return list and list 0  or None   That works in many cases  but it will only work if list 0  is not equal to 0  False  or an empty string   If list 0  is 0  False  or an empty string  the method will incorrectly return None           I ve created this bug in my own code one too many times

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The OP s solution is nearly there  there are just a few things to make it more Pythonic   For one  there s no need to get the length of the list  Empty lists in Python evaluate to False in an if check  Just simply say  if list    Additionally  it s a very Bad Idea to assign to variables that overlap with reserved words   list  is a reserved word in Python   So let s change that to  some list   get list   if some list    A really important point that a lot of solutions here miss is that all Python functions methods return None by default  Try the following below   def does nothing        pass  foo   does nothing   print foo   Unless you need to return None to terminate a function early  it s unnecessary to explicitly return None  Quite succinctly  just return the first entry  should it exist   some list   get list   if some list      return list 0    And finally  perhaps this was implied  but just to be explicit  because explicit is better than implicit   you should not have your function get the list from another function  just pass it in as a parameter  So  the final result would be  def get first item some list        if some list          return list 0   my list   get list   first item   get first item my list    As I said  the OP was nearly there  and just a few touches give it the Python flavor you re looking for

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Out of curiosity  I ran timings on two of the solutions  The solution which uses a return statement to prematurely end a for loop is slightly more costly on my machine with Python 2 5 1  I suspect this has to do with setting up the iterable   import random import timeit  def index first item some list       if some list          return some list 0    def return first item some list       for item in some list          return item   empty lists      for i in range 10000       empty lists append      assert empty lists 0  is not empty lists 1   full lists      for i in range 10000       full lists append list  random random   for i in range 10      mixed lists   empty lists  50000    full lists  50000  random shuffle mixed lists   if   name         main         ENV    import firstitem      test data     empty lists    full lists    mixed lists       funcs     index first item    return first item       for data in test data          print   s     data         for func in funcs              t   timeit Timer  firstitem  s firstitem  s                       func  data   ENV              times   t repeat               avg time   sum times    len times              print     s     func             for time in times                  print       f seconds    time             print       f seconds avg     avg time   These are the timings I got    empty lists    index first item      0 748353 seconds     0 741086 seconds     0 741191 seconds     0 743543 seconds avg    return first item      0 785511 seconds     0 822178 seconds     0 782846 seconds     0 796845 seconds avg  full lists    index first item      0 762618 seconds     0 788040 seconds     0 786849 seconds     0 779169 seconds avg    return first item      0 802735 seconds     0 878706 seconds     0 808781 seconds     0 830074 seconds avg  mixed lists    index first item      0 791129 seconds     0 743526 seconds     0 744441 seconds     0 759699 seconds avg    return first item      0 784801 seconds     0 785146 seconds     0 840193 seconds     0 803380 seconds avg

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Using the and-or trick   a   get list   return a and a 0  or None

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for item in get list        return item

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The most python idiomatic way is to use the next   on a iterator since list is iterable  just like what  J F Sebastian put in the comment on Dec 13  2011   next iter the list   None  This returns None if the list is empty  see next   Python 2 6    or if you know for sure the list is not empty   iter the list  next   see iterator next   Python 2 2

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get list   or  None   0    That should work   BTW I didn t use the variable list  because that overwrites the builtin list   function   Edit   I had a slightly simpler  but wrong version here earlier

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How about this    my list and my list 0   or None  Note  This should work fine for lists of objects but it might return incorrect answer in case of number or string list per the comments below

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Borrowing more itertools first true code yields something decently readable  def first true iterable  default None  pred None       return next filter pred  iterable   default   def get first non default items list  default None       return first true items list  default  pred lambda x  x  default

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Python idiom to return first item or None    The most Pythonic approach is what the most upvoted answer demonstrated  and it was the first thing to come to my mind when I read the question  Here s how to use it  first if the possibly empty list is passed into a function   def get first l        return l 0  if l else None   And if the list is returned from a get list function   l   get list   return l 0  if l else None   Other ways demonstrated to do this here  with explanations  for  When I began trying to think of clever ways to do this  this is the second thing I thought of   for item in get list        return item   This presumes the function ends here  implicitly returning None if get list returns an empty list  The below explicit code is exactly equivalent   for item in get list        return item return None   if some list  The following was also proposed  I corrected the incorrect variable name  which also uses the implicit None  This would be preferable to the above  as it uses the logical check instead of an iteration that may not happen  This should be easier to understand immediately what is happening  But if we re writing for readability and maintainability  we should also add the explicit return None at the end   some list   get list   if some list      return some list 0    slice or  None  and select zeroth index  This one is also in the most up-voted answer   return  get list    1  or  None   0    The slice is unnecessary  and creates an extra one-item list in memory   The following should be more performant  To explain  or returns the second element if the first is False in a boolean context  so if get list returns an empty list  the expression contained in the parentheses will return a list with  None   which will then be accessed by the 0 index   return  get list   or  None   0    The next one uses the fact that and returns the second item if the first is True in a boolean context  and since it references my list twice  it is no better than the ternary expression  and technically not a one-liner    my list   get list    return  my list and my list 0   or None   next  Then we have the following clever use of the builtin next and iter  return next iter get list     None    To explain  iter returns an iterator with a  next method      next   in Python 3   Then the builtin next calls that  next method  and if the iterator is exhausted  returns the default we give  None   redundant ternary expression  a if b else c  and circling back  The below was proposed  but the inverse would be preferable  as logic is usually better understood in the positive instead of the negative  Since get list is called twice  unless the result is memoized in some way  this would perform poorly   return None if not get list   else get list   0    The better inverse   return get list   0  if get list   else None   Even better  use a local variable so that get list is only called one time  and you have the recommended Pythonic solution first discussed   l   get list   return l 0  if l else None

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isn t the idiomatic python equivalent to C-style ternary operators   cond and true expr or false expr   ie    list   get list   return list and list 0  or None

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Frankly speaking  I do not think there is a better idiom  your is clear and terse - no need for anything  better   Maybe  but this is really a matter of taste  you could change if len list   gt  0  with if list  - an empty list will always evaluate to False   On a related note  Python is not Perl  no pun intended    you do not have to get the coolest code possible  Actually  the worst code I have seen in Python  was also very cool  -  and completely unmaintainable   By the way  most of the solution I have seen here do not take into consideration when list 0  evaluates to False  e g  empty string  or zero  - in this case  they all return None and not the correct element

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You could use Extract Method  In other words extract that code into a method which you d then call   I wouldn t try to compress it much more  the one liners seem harder to read than the verbose version  And if you use Extract Method  it s a one liner

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Regarding idioms  there is an itertools recipe called nth   From itertools recipes   def nth iterable  n  default None        Returns the nth item or a default value      return next islice iterable  n  None   default    If you want one-liners  consider installing a library that implements this recipe for you  e g  more itertools   import more itertools as mit  mit nth  3  2  1   0    3  mit nth     0                                                default is  None    None   Another tool is available that only returns the first item  called more itertools first   mit first  3  2  1     3  mit first     default None    None   These itertools scale generically for any iterable  not only for lists

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The OP s solution is nearly there  there are just a few things to make it more Pythonic   For one  there s no need to get the length of the list  Empty lists in Python evaluate to False in an if check  Just simply say  if list    Additionally  it s a very Bad Idea to assign to variables that overlap with reserved words   list  is a reserved word in Python   So let s change that to  some list   get list   if some list    A really important point that a lot of solutions here miss is that all Python functions methods return None by default  Try the following below   def does nothing        pass  foo   does nothing   print foo   Unless you need to return None to terminate a function early  it s unnecessary to explicitly return None  Quite succinctly  just return the first entry  should it exist   some list   get list   if some list      return list 0    And finally  perhaps this was implied  but just to be explicit  because explicit is better than implicit   you should not have your function get the list from another function  just pass it in as a parameter  So  the final result would be  def get first item some list        if some list          return list 0   my list   get list   first item   get first item my list    As I said  the OP was nearly there  and just a few touches give it the Python flavor you re looking for

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Borrowing more itertools first true code yields something decently readable  def first true iterable  default None  pred None       return next filter pred  iterable   default   def get first non default items list  default None       return first true items list  default  pred lambda x  x  default

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Using the and-or trick   a   get list   return a and a 0  or None

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Not sure how pythonic this is but until there is a first function in the library I include this in the source:

first = lambda l, default=None: next(iter(l or []), default)

It's just one line (conforms to black) and avoids dependencies.

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Out of curiosity  I ran timings on two of the solutions  The solution which uses a return statement to prematurely end a for loop is slightly more costly on my machine with Python 2 5 1  I suspect this has to do with setting up the iterable   import random import timeit  def index first item some list       if some list          return some list 0    def return first item some list       for item in some list          return item   empty lists      for i in range 10000       empty lists append      assert empty lists 0  is not empty lists 1   full lists      for i in range 10000       full lists append list  random random   for i in range 10      mixed lists   empty lists  50000    full lists  50000  random shuffle mixed lists   if   name         main         ENV    import firstitem      test data     empty lists    full lists    mixed lists       funcs     index first item    return first item       for data in test data          print   s     data         for func in funcs              t   timeit Timer  firstitem  s firstitem  s                       func  data   ENV              times   t repeat               avg time   sum times    len times              print     s     func             for time in times                  print       f seconds    time             print       f seconds avg     avg time   These are the timings I got    empty lists    index first item      0 748353 seconds     0 741086 seconds     0 741191 seconds     0 743543 seconds avg    return first item      0 785511 seconds     0 822178 seconds     0 782846 seconds     0 796845 seconds avg  full lists    index first item      0 762618 seconds     0 788040 seconds     0 786849 seconds     0 779169 seconds avg    return first item      0 802735 seconds     0 878706 seconds     0 808781 seconds     0 830074 seconds avg  mixed lists    index first item      0 791129 seconds     0 743526 seconds     0 744441 seconds     0 759699 seconds avg    return first item      0 784801 seconds     0 785146 seconds     0 840193 seconds     0 803380 seconds avg

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my list 0  if len my list  else None

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def head iterable       try          return iter iterable  next       except StopIteration          return None  print head xrange 42  1000     42 print head                     None   BTW  I d rework your general program flow into something like this   lists           first    list          second    list          third    list      def do something element       if not element          return     else            do something         pass  for li in lists      do something head li      Avoiding repetition whenever possible

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get list   or  None   0    That should work   BTW I didn t use the variable list  because that overwrites the builtin list   function   Edit   I had a slightly simpler  but wrong version here earlier

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The best way is this   a   get list   return a 0  if a else None   You could also do it in one line  but it s much harder for the programmer to read   return  get list    1  or  None   0

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Python 2 6   next iter your list   None    If your list can be None   next iter your list or      None    Python 2 4  def get first iterable  default None       if iterable          for item in iterable              return item     return default   Example   x   get first get first list    if x          y   get first get second list    if y            Another option is to inline the above function   for x in get first list   or           process x     break   process at most one item for y in get second list   or           process y     break   To avoid break you could write   for x in yield first get first list         x   process x for y in yield first get second list         y   process y   Where   def yield first iterable       for item in iterable or             yield item         return

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Probably not the fastest solution  but nobody mentioned this option   dict enumerate get list     get 0    if get list   can return None you can use   dict enumerate get list   or      get 0    Advantages   -one line  -you just call get list   once  -easy to understand

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The best way is this   a   get list   return a 0  if a else None   You could also do it in one line  but it s much harder for the programmer to read   return  get list    1  or  None   0

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The OP s solution is nearly there  there are just a few things to make it more Pythonic   For one  there s no need to get the length of the list  Empty lists in Python evaluate to False in an if check  Just simply say  if list    Additionally  it s a very Bad Idea to assign to variables that overlap with reserved words   list  is a reserved word in Python   So let s change that to  some list   get list   if some list    A really important point that a lot of solutions here miss is that all Python functions methods return None by default  Try the following below   def does nothing        pass  foo   does nothing   print foo   Unless you need to return None to terminate a function early  it s unnecessary to explicitly return None  Quite succinctly  just return the first entry  should it exist   some list   get list   if some list      return list 0    And finally  perhaps this was implied  but just to be explicit  because explicit is better than implicit   you should not have your function get the list from another function  just pass it in as a parameter  So  the final result would be  def get first item some list        if some list          return list 0   my list   get list   first item   get first item my list    As I said  the OP was nearly there  and just a few touches give it the Python flavor you re looking for

User · Answer

Using the and-or trick   a   get list   return a and a 0  or None

User · Answer

for item in get list        return item

User · Answer

isn t the idiomatic python equivalent to C-style ternary operators   cond and true expr or false expr   ie    list   get list   return list and list 0  or None

User · Answer

Several people have suggested doing something like this   list   get list   return list and list 0  or None   That works in many cases  but it will only work if list 0  is not equal to 0  False  or an empty string   If list 0  is 0  False  or an empty string  the method will incorrectly return None           I ve created this bug in my own code one too many times

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Probably not the fastest solution  but nobody mentioned this option   dict enumerate get list     get 0    if get list   can return None you can use   dict enumerate get list   or      get 0    Advantages   -one line  -you just call get list   once  -easy to understand

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How about this    my list and my list 0   or None  Note  This should work fine for lists of objects but it might return incorrect answer in case of number or string list per the comments below

User · Answer

You could use Extract Method  In other words extract that code into a method which you d then call   I wouldn t try to compress it much more  the one liners seem harder to read than the verbose version  And if you use Extract Method  it s a one liner

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try      return a 0  except IndexError      return None

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try      return a 0  except IndexError      return None

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my list 0  if len my list  else None

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Python 2 6   next iter your list   None    If your list can be None   next iter your list or      None    Python 2 4  def get first iterable  default None       if iterable          for item in iterable              return item     return default   Example   x   get first get first list    if x          y   get first get second list    if y            Another option is to inline the above function   for x in get first list   or           process x     break   process at most one item for y in get second list   or           process y     break   To avoid break you could write   for x in yield first get first list         x   process x for y in yield first get second list         y   process y   Where   def yield first iterable       for item in iterable or             yield item         return

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Python idiom to return first item or None    The most Pythonic approach is what the most upvoted answer demonstrated  and it was the first thing to come to my mind when I read the question  Here s how to use it  first if the possibly empty list is passed into a function   def get first l        return l 0  if l else None   And if the list is returned from a get list function   l   get list   return l 0  if l else None   Other ways demonstrated to do this here  with explanations  for  When I began trying to think of clever ways to do this  this is the second thing I thought of   for item in get list        return item   This presumes the function ends here  implicitly returning None if get list returns an empty list  The below explicit code is exactly equivalent   for item in get list        return item return None   if some list  The following was also proposed  I corrected the incorrect variable name  which also uses the implicit None  This would be preferable to the above  as it uses the logical check instead of an iteration that may not happen  This should be easier to understand immediately what is happening  But if we re writing for readability and maintainability  we should also add the explicit return None at the end   some list   get list   if some list      return some list 0    slice or  None  and select zeroth index  This one is also in the most up-voted answer   return  get list    1  or  None   0    The slice is unnecessary  and creates an extra one-item list in memory   The following should be more performant  To explain  or returns the second element if the first is False in a boolean context  so if get list returns an empty list  the expression contained in the parentheses will return a list with  None   which will then be accessed by the 0 index   return  get list   or  None   0    The next one uses the fact that and returns the second item if the first is True in a boolean context  and since it references my list twice  it is no better than the ternary expression  and technically not a one-liner    my list   get list    return  my list and my list 0   or None   next  Then we have the following clever use of the builtin next and iter  return next iter get list     None    To explain  iter returns an iterator with a  next method      next   in Python 3   Then the builtin next calls that  next method  and if the iterator is exhausted  returns the default we give  None   redundant ternary expression  a if b else c  and circling back  The below was proposed  but the inverse would be preferable  as logic is usually better understood in the positive instead of the negative  Since get list is called twice  unless the result is memoized in some way  this would perform poorly   return None if not get list   else get list   0    The better inverse   return get list   0  if get list   else None   Even better  use a local variable so that get list is only called one time  and you have the recommended Pythonic solution first discussed   l   get list   return l 0  if l else None

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isn t the idiomatic python equivalent to C-style ternary operators   cond and true expr or false expr   ie    list   get list   return list and list 0  or None

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if mylist                print mylist 0       else          print None

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for item in get list        return item

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Out of curiosity  I ran timings on two of the solutions  The solution which uses a return statement to prematurely end a for loop is slightly more costly on my machine with Python 2 5 1  I suspect this has to do with setting up the iterable   import random import timeit  def index first item some list       if some list          return some list 0    def return first item some list       for item in some list          return item   empty lists      for i in range 10000       empty lists append      assert empty lists 0  is not empty lists 1   full lists      for i in range 10000       full lists append list  random random   for i in range 10      mixed lists   empty lists  50000    full lists  50000  random shuffle mixed lists   if   name         main         ENV    import firstitem      test data     empty lists    full lists    mixed lists       funcs     index first item    return first item       for data in test data          print   s     data         for func in funcs              t   timeit Timer  firstitem  s firstitem  s                       func  data   ENV              times   t repeat               avg time   sum times    len times              print     s     func             for time in times                  print       f seconds    time             print       f seconds avg     avg time   These are the timings I got    empty lists    index first item      0 748353 seconds     0 741086 seconds     0 741191 seconds     0 743543 seconds avg    return first item      0 785511 seconds     0 822178 seconds     0 782846 seconds     0 796845 seconds avg  full lists    index first item      0 762618 seconds     0 788040 seconds     0 786849 seconds     0 779169 seconds avg    return first item      0 802735 seconds     0 878706 seconds     0 808781 seconds     0 830074 seconds avg  mixed lists    index first item      0 791129 seconds     0 743526 seconds     0 744441 seconds     0 759699 seconds avg    return first item      0 784801 seconds     0 785146 seconds     0 840193 seconds     0 803380 seconds avg

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get list   or  None   0    That should work   BTW I didn t use the variable list  because that overwrites the builtin list   function   Edit   I had a slightly simpler  but wrong version here earlier

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Several people have suggested doing something like this   list   get list   return list and list 0  or None   That works in many cases  but it will only work if list 0  is not equal to 0  False  or an empty string   If list 0  is 0  False  or an empty string  the method will incorrectly return None           I ve created this bug in my own code one too many times

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try      return a 0  except IndexError      return None

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def head iterable       try          return iter iterable  next       except StopIteration          return None  print head xrange 42  1000     42 print head                     None   BTW  I d rework your general program flow into something like this   lists           first    list          second    list          third    list      def do something element       if not element          return     else            do something         pass  for li in lists      do something head li      Avoiding repetition whenever possible

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Frankly speaking  I do not think there is a better idiom  your is clear and terse - no need for anything  better   Maybe  but this is really a matter of taste  you could change if len list   gt  0  with if list  - an empty list will always evaluate to False   On a related note  Python is not Perl  no pun intended    you do not have to get the coolest code possible  Actually  the worst code I have seen in Python  was also very cool  -  and completely unmaintainable   By the way  most of the solution I have seen here do not take into consideration when list 0  evaluates to False  e g  empty string  or zero  - in this case  they all return None and not the correct element

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try      return a 0  except IndexError      return None

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The best way is this   a   get list   return a 0  if a else None   You could also do it in one line  but it s much harder for the programmer to read   return  get list    1  or  None   0

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My use case was only to set the value of a local variable   Personally I found the try and except style cleaner to read  items    10  20  try  first item   items 0  except IndexError  first item   None print first item   than slicing a list   items    10  20  first item    items  1  or  None     0  print first item

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if mylist                print mylist 0       else          print None

User · Answer

The best way is this   a   get list   return a 0  if a else None   You could also do it in one line  but it s much harder for the programmer to read   return  get list    1  or  None   0

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The most python idiomatic way is to use the next   on a iterator since list is iterable  just like what  J F Sebastian put in the comment on Dec 13  2011   next iter the list   None  This returns None if the list is empty  see next   Python 2 6    or if you know for sure the list is not empty   iter the list  next   see iterator next   Python 2 2

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def head iterable       try          return iter iterable  next       except StopIteration          return None  print head xrange 42  1000     42 print head                     None   BTW  I d rework your general program flow into something like this   lists           first    list          second    list          third    list      def do something element       if not element          return     else            do something         pass  for li in lists      do something head li      Avoiding repetition whenever possible

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Regarding idioms  there is an itertools recipe called nth   From itertools recipes   def nth iterable  n  default None        Returns the nth item or a default value      return next islice iterable  n  None   default    If you want one-liners  consider installing a library that implements this recipe for you  e g  more itertools   import more itertools as mit  mit nth  3  2  1   0    3  mit nth     0                                                default is  None    None   Another tool is available that only returns the first item  called more itertools first   mit first  3  2  1     3  mit first     default None    None   These itertools scale generically for any iterable  not only for lists

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def head iterable       try          return iter iterable  next       except StopIteration          return None  print head xrange 42  1000     42 print head                     None   BTW  I d rework your general program flow into something like this   lists           first    list          second    list          third    list      def do something element       if not element          return     else            do something         pass  for li in lists      do something head li      Avoiding repetition whenever possible

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Frankly speaking  I do not think there is a better idiom  your is clear and terse - no need for anything  better   Maybe  but this is really a matter of taste  you could change if len list   gt  0  with if list  - an empty list will always evaluate to False   On a related note  Python is not Perl  no pun intended    you do not have to get the coolest code possible  Actually  the worst code I have seen in Python  was also very cool  -  and completely unmaintainable   By the way  most of the solution I have seen here do not take into consideration when list 0  evaluates to False  e g  empty string  or zero  - in this case  they all return None and not the correct element

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Frankly speaking  I do not think there is a better idiom  your is clear and terse - no need for anything  better   Maybe  but this is really a matter of taste  you could change if len list   gt  0  with if list  - an empty list will always evaluate to False   On a related note  Python is not Perl  no pun intended    you do not have to get the coolest code possible  Actually  the worst code I have seen in Python  was also very cool  -  and completely unmaintainable   By the way  most of the solution I have seen here do not take into consideration when list 0  evaluates to False  e g  empty string  or zero  - in this case  they all return None and not the correct element

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Out of curiosity  I ran timings on two of the solutions  The solution which uses a return statement to prematurely end a for loop is slightly more costly on my machine with Python 2 5 1  I suspect this has to do with setting up the iterable   import random import timeit  def index first item some list       if some list          return some list 0    def return first item some list       for item in some list          return item   empty lists      for i in range 10000       empty lists append      assert empty lists 0  is not empty lists 1   full lists      for i in range 10000       full lists append list  random random   for i in range 10      mixed lists   empty lists  50000    full lists  50000  random shuffle mixed lists   if   name         main         ENV    import firstitem      test data     empty lists    full lists    mixed lists       funcs     index first item    return first item       for data in test data          print   s     data         for func in funcs              t   timeit Timer  firstitem  s firstitem  s                       func  data   ENV              times   t repeat               avg time   sum times    len times              print     s     func             for time in times                  print       f seconds    time             print       f seconds avg     avg time   These are the timings I got    empty lists    index first item      0 748353 seconds     0 741086 seconds     0 741191 seconds     0 743543 seconds avg    return first item      0 785511 seconds     0 822178 seconds     0 782846 seconds     0 796845 seconds avg  full lists    index first item      0 762618 seconds     0 788040 seconds     0 786849 seconds     0 779169 seconds avg    return first item      0 802735 seconds     0 878706 seconds     0 808781 seconds     0 830074 seconds avg  mixed lists    index first item      0 791129 seconds     0 743526 seconds     0 744441 seconds     0 759699 seconds avg    return first item      0 784801 seconds     0 785146 seconds     0 840193 seconds     0 803380 seconds avg

[python] Python idiom to return first item or None

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