How exactly does the python any function work

Question

In the python docs page for any  the equivalent code for the any   function is given as   def any iterable       for element in iterable          if element              return True     return False   How does this function know what element I wanna test if call it in this form   any x  gt  0 for x in list    From the function definition  all I can see is that I m passing an iterable object  How does the for loop know I am looking for something  gt  0

User · Answer

gt  gt  gt  names     King    Queen    Joker    gt  gt  gt  any n in  King and john  for n in names  True   gt  gt  gt  all n in  King and Queen  for n in names  False   It just reduce several line of code into one  You don t have to write lengthy code like   for n in names      if n in  King and john          print True     else         print False

User · Answer

Simply saying  any   does this work   according to the condition even if it encounters one fulfilling value in the list  it returns true  else it returns false   list    2 -3 -4 5 6   a   any x gt 0 for x in lst   print a  True   list    2 3 4 5 6 7   a   any x lt 0 for x in lst   print a  False

User · Answer

x  gt  0 for x in list  in that function call creates a generator expression eg    gt  gt  gt  nums    1  2  -1  9  -5   gt  gt  gt  genexp    x  gt  0 for x in nums   gt  gt  gt  for x in genexp          print x   True True False True False   Which any uses  and shortcircuits on encountering the first object that evaluates True

User · Answer

If you use any lst  you see that lst is the iterable  which is a list of some items  If it contained  0  False      0 0          None   which all have boolean values of False  then any lst  would be False  If lst also contained any of the following  -1  True   X   0 00001   all of which evaluate to True  then any lst  would be True   In the code you posted  x  gt  0 for x in lst  this is a different kind of iterable  called a generator expression  Before generator expressions were added to Python  you would have created a list comprehension  which looks very similar  but with surrounding    s   x  gt  0 for x in lst   From the lst containing  -1  -2  10  -4  20   you would get this comprehended list   False  False  True  False  True   This internal value would then get passed to the any function  which would return True  since there is at least one True value   But with generator expressions  Python no longer has to create that internal list of True s  and False s   the values will be generated as the any function iterates through the values generated one at a time by the generator expression  And  since any short-circuits  it will stop iterating as soon as it sees the first True value  This would be especially handy if you created lst using something like lst   range -1 int 1e9    or xrange if you are using Python2 x   Even though this expression will generate over a billion entries  any only has to go as far as the third entry when it gets to 1  which evaluates True for x gt 0  and so any can return True    If you had created a list comprehension  Python would first have had to create the billion-element list in memory  and then pass that to any  But by using a generator expression  you can have Python s builtin functions like any and all break out early  as soon as a True or False value is seen

User · Answer

It s because the iterable is    x  gt  0 for x in list    Note that x  gt  0 returns either True or False and thus you have an iterable of booleans

[python] How exactly does the python any() function work?

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