Why does range start end not include end

Question

gt  gt  gt  range 1 11    gives you   1 2 3 4 5 6 7 8 9 10    Why not 1-11   Did they just decide to do it like that at random or does it have some value I am not seeing

User · Answer

Exclusive ranges do have some benefits   For one thing each item in range 0 n  is a valid index for lists of length n   Also range 0 n  has a length of n  not n 1 which an inclusive range would

User · Answer

The range n  in python returns from 0 to n-1  Respectively  the range 1 n  from 1 to n-1  So  if you want to omit the first value and get also the last value  n  you can do it very simply using the following code  for i in range 1  n   1           print i   prints from 1 to n

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The length of the range is the top value minus the bottom value   It s very similar to something like   for  var i   1  i  lt  11  i            i goes from 1 to 10 in here     in a C-style language   Also like Ruby s range   1   11  this is a range from 1 to 10   However  Ruby recognises that many times you ll want to include the terminal value and offers the alternative syntax   1  10  this is also a range from 1 to 10

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Because it s more common to call range 0  10  which returns  0 1 2 3 4 5 6 7 8 9  which contains 10 elements which equals len range 0  10    Remember that programmers prefer 0-based indexing   Also  consider the following common code snippet   for i in range len li        pass   Could you see that if range   went up to exactly len li  that this would be problematic  The programmer would need to explicitly subtract 1  This also follows the common trend of programmers preferring for int i   0  i  lt  10  i    over for int i   0  i  lt   9  i      If you are calling range with a start of 1 frequently  you might want to define your own function    gt  gt  gt  def range1 start  end           return range start  end 1       gt  gt  gt  range1 1  10   1  2  3  4  5  6  7  8  9  10

User · Answer

Although there are some useful algorithmic explanations here  I think it may help to add some simple  real life  reasoning as to why it works this way  which I have found useful when introducing the subject to young newcomers   With something like  range 1 10   confusion can arise from thinking that pair of parameters represents the  start and end    It is actually start and  stop    Now  if it were the  end  value then  yes  you might expect that number would be included as the final entry in the sequence  But it is not the  end    Others mistakenly call that parameter  count  because if you only ever use  range n   then it does  of course  iterate  n  times  This logic breaks down when you add the start parameter   So the key point is to remember its name   stop   That means it is the point at which  when reached  iteration will stop immediately  Not after that point   So  while  start  does indeed represent the first value to be included  on reaching the  stop  value it  breaks  rather than continuing to process  that one as well  before stopping   One analogy that I have used in explaining this to kids is that  ironically  it is better behaved than kids  It doesn t stop after it supposed to - it stops immediately without finishing what it was doing   They get this       Another analogy - when you drive a car you don t pass a stop yield  give way  sign and end up with it sitting somewhere next to  or behind  your car  Technically you still haven t reached it when you do stop  It is not included in the  things you passed on your journey    I hope some of that helps in explaining to Pythonitos Pythonitas

User · Answer

It s just more convenient to reason about in many cases   Basically  we could think of a range as an interval between start and end  If start  lt   end  the length of the interval between them  is end - start  If len was actually defined as the length  you d have   len range start  end      start - end   However  we count the integers included in the range instead of measuring the length of the interval  To keep the above property true  we should include one of the endpoints and exclude the other   Adding the step parameter is like introducing a unit of length  In that case  you d expect  len range start  end  step       start - end    step   for length  To get the count  you just use integer division

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Basically in python range n  iterates n times  which is of exclusive nature that is why it does not give last value when it is being printed  we can create a function which gives  inclusive value it means it will also print last value mentioned in range   def main        for i in inclusive range 25           print i  sep        def inclusive range  args       numargs   len args      if numargs    0          raise TypeError  you need to write at least a value       elif numargs    1          stop   args 0          start   0         step   1     elif numargs    2           start  stop    args         step   1     elif numargs    3           start  stop  step    args     else          raise TypeError  Inclusive range was expected at most 3 arguments got     format numargs       i   start     while i  lt   stop          yield i         i    step   if   name         main         main

User · Answer

Consider the code  for i in range 10       print  You ll see this 10 times   i   The idea is that you get a list of length y-x  which you can  as you see above  iterate over    Read up on the python docs for range - they consider for-loop iteration the primary usecase

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It s also useful for splitting ranges  range a b  can be split into range a  x  and range x  b   whereas with inclusive range you would write either x-1 or x 1  While you rarely need to split ranges  you do tend to split lists quite often  which is one of the reasons slicing a list l a b  includes the a-th element but not the b-th  Then range having the same property makes it nicely consistent

User · Answer

It works well in combination with zero-based indexing and len    For example  if you have 10 items in a list x  they are numbered 0-9  range len x   gives you 0-9   Of course  people will tell you it s more Pythonic to do for item in x or for index  item in enumerate x  rather than for i in range len x     Slicing works that way too  foo 1 4  is items 1-3 of foo  keeping in mind that item 1 is actually the second item due to the zero-based indexing   For consistency  they should both work the same way   I think of it as   the first number you want  followed by the first number you don t want   If you want 1-10  the first number you don t want is 11  so it s range 1  11    If it becomes cumbersome in a particular application  it s easy enough to write a little helper function that adds 1 to the ending index and calls range

[python] Why does range(start, end) not include end?

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