How to loop through all but the last item of a list

Question

I would like to loop through a list checking each item against the one following it   Is there a way I can loop through all but the last item using for x in y  I would prefer to do it without using indexes if I can   Note  freespace answered my actual question  which is why I accepted the answer  but SilentGhost answered the question I should have asked   Apologies for the confusion

User · Accepted Answer

for x in y  -1    If y is a generator  then the above will not work

User · Answer

if you meant comparing nth item with n 1 th item in the list you could also do with   gt  gt  gt  for i in range len list  -1             print list i  gt list i 1    note there is no hard coding going on there  This should be ok unless you feel otherwise

User · Answer

To compare each item with the next one in an iterator without instantiating a list   import itertools it    x for x in range 10   data1  data2   itertools tee it  data2 next   for a  b in itertools izip data1  data2     print a  b

User · Answer

If you want to get all the elements in the sequence pair wise  use this approach  the pairwise function is from the examples in the itertools module    from itertools import tee  izip  chain  def pairwise seq       a b   tee seq      b next       return izip a b   for current item  next item in pairwise y       if compare current item  next item             do what you have to do   If you need to compare the last value to some special value  chain that value to the end  for current  next item in pairwise chain y   None

User · Answer

This answers what the OP should have asked  i e  traverse a list comparing consecutive elements  excellent SilentGhost answer   yet generalized for any group  n-gram   2  3      n   zip   l start   for start in range 0  n     Examples   l   range 0  4      0  1  2  3   list zip   l start   for start in range 0  2            0  1    1  2    2  3   list zip   l start   for start in range 0  3            0  1  2    1  2  3   list zip   l start   for start in range 0  4            0  1  2  3   list zip   l start   for start in range 0  5               Explanations    l start   generates a a list generator starting from index start  list or  generator  passes all elements to the enclosing function zip as if it was written zip elem1  elem2         Note   AFAIK  this code is as lazy as it can be  Not tested

User · Answer

the easiest way to compare the sequence item with the following   for i  j in zip a  a 1            compare i  the current  to j  the following

[python] How to loop through all but the last item of a list?

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