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. -- https://mail.python.org/mailman/listinfo/python-list
