Generating Cyclic Words in Python

Question

I have an array like

myarray = 'ABCDE'

and I want output as

required_output = [AB,BC,CD,DE,EA]  ## A cyclic form of array 'ABCDE'

I used following code

for i in range(len(myarray) + 1):

    a = i % len(myarray) ; b = i % len(myarray) + 2

    print myarray[a : b]

result I get as

AB , BC, CD, DE, E , AB

what logic I am missing which is causing 'e' to appear instead of 'ea' and also 'ab' should not have appeared ???

Another way I found was to use a loop like this

for i in range(1,len(myarray)):

    print myarray[i-1] + myarray[i]

gives output as

'EA','AB','BC','CD','DE'  ## where the last element 'EA' comes in the begining

Answer 1

It's not too hard to see what's going wrong

>>> myarray = 'ABCDE'
>>> for i in range(len(myarray) + 1):
...     a = i % len(myarray) ; b = i % len(myarray) + 2
...     print a, b, myarray[a: b]
... 
0 2 AB
1 3 BC
2 4 CD
3 5 DE
4 6 E
0 2 AB

There's no way you're going to get a slice like 'EA' without doing something heroic like

>>> myarray[::-4]
'EA'

The + 1 is obviously going to give you one more output than the number of items in myarray

Easy fix is something like this

>>> for i in range(len(myarray)):
...     print (myarray*2)[i:i+2]
... 
AB
BC
CD
DE
EA

Answer 2

You can use zip here:

def cycle(s):
    return [ ''.join(x) for x in zip(s, s[1:]+s[:1])]

>>> cycle('ABCDE')
['AB', 'BC', 'CD', 'DE', 'EA']
>>> cycle('ABCD')
['AB', 'BC', 'CD', 'DA']

Using indexes, similar to your method:

def cycle(s):
    for i in range(len(s)):
        yield s[i] + s[(i+1)%len(s)]

print list(cycle('ABCDE'))
print list(cycle('ABCD'))

Output:

['AB', 'BC', 'CD', 'DE', 'EA']
['AB', 'BC', 'CD', 'DA']

Answer 3

Why not just

print [data[i: (i + 2)] for i in range(len(data) - 1)] + [data[-1] + data[0]]

Output

['AB', 'BC', 'CD', 'DE', 'EA']

Answer 4

[''.join(a) for a in zip(myarray,myarray[1:]+myarray[0])]

output:

['AB', 'BC', 'CD', 'DE', 'EA']

Answer 5

Maybe it helps you:

In [1]: m = 'ABCDE'

In [2]: ml = list(m)

In [3]: zip(ml, ml[1:] + [m[0]])
Out[3]: [('A', 'B'), ('B', 'C'), ('C', 'D'), ('D', 'E'), ('E', 'A')]