IndexError: list index out of range

[Elnaz]

On Tuesday, December 13, 2016 at 12:45:49 PM UTC+3:30, Peter Otten wrote:
> Elnaz wrote:
> 
> > hi
> > i am begginer in python. I have written a code and given this error:
> > IndexError: list index out of range
> > 
> > In my program, I have h=32 bits input. i divide this 32 bits to 4*8 block
> > and every 8-block is n. so n=0:7;(h=int(n/4)) I want to rotate 0 to 7 bits
> > for 2 bits: 0,1,2,3,4,5,6,7--->2,3,4,5,6,7 Iwrite this code:
> > def rottwo(self, X, n, r):
> >         assert r >= 1
> >         temp = [None]*n
> >         for i in range(n-r) :
> >             temp[i] = X[i+r]
> >         for i in range(n-r,n) :
> >             temp[i] = X[i-n+r]
> >         return temp
> > this function work correctly. but I also want to rotate 24 to 31 bits for
> > 5 bits: 24,25,26,27,28,29,30,31-->29,30,31,24,25,26,27,28
> > 
> > when I write this code:
> > def rotfive(self, X, n, r):
> >        assert r >= 1
> >        temp = [None]*n
> >        for i in range(n-r) :
> >             temp[i+24] = X[i+3*n+r]
> >        for i in range(n-r,n) :
> >             temp[i+24] = X[i+2*n+r]
> >        return temp
> > beacase temp is of size n I cannot access index 3*n+i. index on the list
> > temp should be less than equal to n-1 . I son't know how I must correct
> > this!!!!!!!! Is there any one to help me?
> > thanks in advanse.
> 
> I think you are making this harder than necessary. Python slices make 
> accessing parts of a list quite elegant:
> 
> >>> items
> [0, 10, 20, 30, 40, 50, 60, 70, 80, 90]
> >>> items[2:5]
> [20, 30, 40]
> >>> items[3:]
> [30, 40, 50, 60, 70, 80, 90]
> 
> You can use this to implement a function that creates a rotated list with an 
> arbitrary offset:
> 
> >>> def rot(items, offset):
> ...     return items[offset:] + items[:offset]
> ... 
> >>> rot(items, 2)
> [20, 30, 40, 50, 60, 70, 80, 90, 0, 10]
> >>> rot(items, 7)
> [70, 80, 90, 0, 10, 20, 30, 40, 50, 60]
> >>> rot(items, -2)
> [80, 90, 0, 10, 20, 30, 40, 50, 60, 70]
> 
> To rotate part of a list extract that part using slice notation, rotate it 
> and write it back:
> 
> >>> def rot_part(items, offset, start, stop):
> ...     items = list(items)
> ...     items[start:stop] = rot(items[start:stop], offset)
> ...     return items
> ... 
> >>> rot_part(range(32), 5, 24, 32)
> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 
> 21, 22, 23, 29, 30, 31, 24, 25, 26, 27, 28]
> 
> If you pass a list as the first argument
> 
> items = list(items) 
> 
> makes of copy of the list, but it will also convert an arbitrary iterable to 
> a list. That's why I can pass the range object.



i really appreciate your help. it works.