How do Python s any and all functions work

Question

I m trying to understand how the any   and all   Python built-in functions work    I m trying to compare the tuples so that if any value is different then it will return True and if they are all the same it will return False  How are they working in this case to return  False  False  False    d is a defaultdict list    print d  Drd2       1  5  0    1  6  0   print list zip  d  Drd2         1  1    5  6    0  0   print  any x  and not all x  for x in zip  d  Drd2        False  False  False    To my knowledge  this should output      False  True  False    since  1 1  are the same   5 6  are different  and  0 0  are the same    Why is it evaluating to False for all tuples

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I know this is old  but I thought it might be helpful to show what these functions look like in code  This really illustrates the logic  better than text or a table IMO  In reality they are implemented in C rather than pure Python  but these are equivalent   def any iterable       for item in iterable          if item              return True     return False  def all iterable       for item in iterable          if not item              return False     return True   In particular  you can see that the result for empty iterables is just the natural result  not a special case  You can also see the short-circuiting behaviour  it would actually be more work for there not to be short-circuiting   When Guido van Rossum  the creator of Python  first proposed adding any   and all    he explained them by just posting exactly the above snippets of code

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s    eFdss  s   list s  all i islower   for i in s       FALSE any i islower   for i in s       TRUE

User · Answer

The concept is simple       M    1  1    5  6    0  0    1  print  any x  for x in M    True  True  False   only the last tuple does not have any true element  2  print  all x  for x in M    True  True  False   all elements of the last tuple are not true  3  print  not all x  for x in M    False  False  True   NOT operator applied to 2   4  print  any x   and not all x  for x in M    False  False  False   AND operator applied to 1  and 3    if we had M    1  1    5  6    1  0    we could get  False  False  True   in 4    because the last tuple satisfies both conditions  any of its elements is TRUE   and not all elements are TRUE

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list    1 1 1 0  print any list     will return True because there is  1 or True exists print all list     will return False because there is a 0 or False exists return all a   i for i in range 3  int a    0 5    1     when number is divisible it will return False else return True but the whole statement is False

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You can roughly think of any and all as series of logical or and and operators  respectively   any  any will return True when at least one of the elements is Truthy  Read about Truth Value Testing   all  all will return True only when all the elements are Truthy   Truth table    ----------------------------------------- --------- ---------                                                any       all      ----------------------------------------- --------- ---------    All Truthy values                          True      True      ----------------------------------------- --------- ---------    All Falsy values                           False     False     ----------------------------------------- --------- ---------    One Truthy value  all others are Falsy     True      False     ----------------------------------------- --------- ---------    One Falsy value  all others are Truthy     True      False     ----------------------------------------- --------- ---------    Empty Iterable                             False     True      ----------------------------------------- --------- ---------    Note 1  The empty iterable case is explained in the official documentation  like this  any     Return True if any element of the iterable is true  If the iterable is empty  return False   Since none of the elements are true  it returns False in this case    all     Return True if all elements of the iterable are true  or if the iterable is empty     Since none of the elements are false  it returns True in this case      Note 2   Another important thing to know about any and all is  it will short-circuit the execution  the moment they know the result  The advantage is  entire iterable need not be consumed  For example    gt  gt  gt  multiples of 6    not  i   6  for i in range 1  10    gt  gt  gt  any multiples of 6  True  gt  gt  gt  list multiples of 6   False  False  False    Here   not  i   6  for i in range 1  10   is a generator expression which returns True if the current number within 1 and 9 is a multiple of 6  any iterates the multiples of 6 and when it meets 6  it finds a Truthy value  so it immediately returns True  and rest of the multiples of 6 is not iterated  That is what we see when we print list multiples of 6   the result of 7  8 and 9   This excellent thing is used very cleverly in this answer     With this basic understanding  if we look at your code  you do   any x  and not all x    which makes sure that  atleast one of the values is Truthy but not all of them  That is why it is returning  False  False  False   If you really wanted to check if both the numbers are not the same   print  x 0     x 1  for x in zip  d  Drd2

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gt  gt  gt  any  False  False  False   False  gt  gt  gt  any  False  True  False   True  gt  gt  gt  all  False  True  True   False  gt  gt  gt  all  True  True  True   True

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How do Python s any and all functions work    any and all take iterables and return True if any and all  respectively  of the elements are True     gt  gt  gt  any  0  0 0  False       0     all  1  0 0001  True   False      True  True                    -- truthy non-empty string  gt  gt  gt  any  0  0 0  False            all  1  0 0001  True   False          False  False                                                       -- falsey   If the iterables are empty  any returns False  and all returns True    gt  gt  gt  any      all      False  True    I was demonstrating all and any for students in class today  They were mostly confused about the return values for empty iterables  Explaining it this way caused a lot of lightbulbs to turn on   Shortcutting behavior  They  any and all  both look for a condition that allows them to stop evaluating  The first examples I gave required them to evaluate the boolean for each element in the entire list    Note that list literal is not itself lazily evaluated - you could get that with an Iterator - but this is just for illustrative purposes    Here s a Python implementation of any and all   def any iterable       for i in iterable          if i              return True     return False   for an empty iterable  any returns False   def all iterable       for i in iterable          if not i              return False     return True    for an empty iterable  all returns True    Of course  the real implementations are written in C and are much more performant  but you could substitute the above and get the same results for the code in this  or any other  answer   all  all checks for elements to be False  so it can return False   then it returns True if none of them were False    gt  gt  gt  all  1  2  3  4                     has to test to the end  True  gt  gt  gt  all  0  1  2  3  4                  0 is False in a boolean context  False     --stops here   gt  gt  gt  all     True     gets to end  so True    any  The way any works is that it checks for elements to be True  so it can return True   then it returnsFalseif none of them wereTrue     gt  gt  gt  any  0  0 0                         has to test to the end  False  gt  gt  gt  any  1  0  0 0                      1 is True in a boolean context  True      --stops here   gt  gt  gt  any     False     gets to end  so False    I think if you keep in mind the short-cutting behavior  you will intuitively understand how they work without having to reference a Truth Table   Evidence of all and any shortcutting   First  create a noisy iterator   def noisy iterator iterable       for i in iterable          print  yielding     repr i           yield i   and now let s just iterate over the lists noisily  using our examples    gt  gt  gt  all noisy iterator  1  2  3  4    yielding 1 yielding 2 yielding 3 yielding 4 True  gt  gt  gt  all noisy iterator  0  1  2  3  4    yielding 0 False   We can see all stops on the first False boolean check   And any stops on the first True boolean check    gt  gt  gt  any noisy iterator  0  0 0                    yielding 0 yielding 0 0 yielding    yielding    yielding    yielding    False  gt  gt  gt  any noisy iterator  1  0  0 0                    yielding 1 True   The source  Let s look at the source to confirm the above   Here s the source for any   static PyObject   builtin any PyObject  module  PyObject  iterable        PyObject  it   item      PyObject    iternext  PyObject         int cmp       it   PyObject GetIter iterable       if  it    NULL          return NULL      iternext    Py TYPE it - gt tp iternext       for                item   iternext it           if  item    NULL              break          cmp   PyObject IsTrue item           Py DECREF item           if  cmp  lt  0                Py DECREF it               return NULL                    if  cmp  gt  0                Py DECREF it               Py RETURN TRUE                      Py DECREF it       if  PyErr Occurred              if  PyErr ExceptionMatches PyExc StopIteration               PyErr Clear            else             return NULL            Py RETURN FALSE      And here s the source for all   static PyObject   builtin all PyObject  module  PyObject  iterable        PyObject  it   item      PyObject    iternext  PyObject         int cmp       it   PyObject GetIter iterable       if  it    NULL          return NULL      iternext    Py TYPE it - gt tp iternext       for                item   iternext it           if  item    NULL              break          cmp   PyObject IsTrue item           Py DECREF item           if  cmp  lt  0                Py DECREF it               return NULL                    if  cmp    0                Py DECREF it               Py RETURN FALSE                      Py DECREF it       if  PyErr Occurred              if  PyErr ExceptionMatches PyExc StopIteration               PyErr Clear            else             return NULL            Py RETURN TRUE

User · Answer

The code in question you re asking about comes from my answer given here   It was intended to solve the problem of comparing multiple bit arrays - i e  collections of 1 and 0  any and all are useful when you can rely on the  quot truthiness quot  of values - i e  their value in a boolean context   1 is True and 0 is False  a convenience which that answer leveraged   5 happens to also be True  so when you mix that into your possible inputs    well   Doesn t work  You could instead do something like this   len set x    gt  1 for x in zip  d  Drd2      It lacks the aesthetics of the previous answer  I really liked the look of any x  and not all x    but it gets the job done

[python] How do Python's any and all functions work?

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