从字符串创建特定列表

Question

Edited according to comments:

I would like to use the strings 'ABC' and '123' to create the list

['A1','B2','C3','A3','C1']

The logic would be to pair the first string with the second string in sequence and then again backwards:

forwards: A1, B2, C3 backwards: A3, B2, C1

B2 only appears once as the final list should be distinct values.

I should be able to expand each of the two strings(they will always match in length) and have the same result pattern.

I tried a couple of things but I would like to know if there is a more pythonic way to accomplish this.

Answer 1

The following solutions will work in Python 3.x,

from collections import OrderedDict

s1 ='ABC'
s2 = '123'

result = list(OrderedDict.fromkeys(first + second for first, second in zip(s1 + s1, s2 + s2[::-1])))
print(result)

Output

['A1', 'B2', 'C3', 'A3', 'C1']

This first solution assumes you only need to repeat the iterables once. If you have to repeat the shortest iterable more than once you could use cycle to iterate several times over it:

from itertools import cycle

s1 ='ABC'
s2 = '123'

seen = set()
result = []
for first, second in zip(cycle(s1), s2 + s2[::-1]):
    first_second = first + second
    if first_second not in seen:
        seen.add(first_second)
        result.append(first_second)

print(result)

Output

['A1', 'B2', 'C3', 'A3', 'C1']

The idea in this second solution is to use a set of seen elements and only add to the final result if not seen. Finally you could combine the solutions and use cycle and OrderedDict :

from itertools import cycle
from collections import OrderedDict

s1 ='ABC'
s2 = '123'

result = list(OrderedDict.fromkeys(first + second for first, second in zip(cycle(s1), s2 + s2[::-1])))
print(result)

Output

['A1', 'B2', 'C3', 'A3', 'C1']

Answer 2

If version greater than 3.6:

print(list(map(''.join,list(dict.fromkeys(list(zip(s1,s2))+list(zip(s1,s2[::-1])))))))

Output:

['A1', 'B2', 'C3', 'A3', 'C1']

Answer 3

I tried a couple of things but I would like to know if there is a more pythonic way to accomplish this.

Without saying what you've tried, it's hard to suggest an alternative, pythonic or otherwise. Looking at what you're doing, it seems you're constructing a mapping between sets of the form:

This is about as atomic as it gets with respect to logical relationships; I'm not sure there's any method that would be quicker than a dumb-as-a-rock string concatenation by index:

x = 'ABC'
y = '123'

new_list = [x[0] + y[0], x[1]+y[1], x[2]+y[2], x[0]+y[2], x[2]+y[0]]

Output:

['A1', 'B2', 'C3', 'A3', 'C1']