Python - sort strings / numeric

Question

My problem, I would like to sort the below list (using Python)

my_list = ['2', '1', '1+', '1-', '2+', '2-']

into

my_list = ['1+', '1', '1-', '2+', '2', '2-']

Edit:

I tried sorted which gives me ['1', '1+', '1-', '2', '2+', '2-']

Therefore, the order of '1' and '1+' should be changed, or '2+' and '2', etc. for all other numbers as well.

Answer 1

Arbitrary rules call for an arbitrary expendable solution: I am relying on the fact that tuples sort element by element, so the numbers 0 , 1 , 2 serve as priorities:

def plus_before_minus(item):
    number = item.rstrip('+-')
    if item.endswith('+'):
        return (number, 0)
    elif item.endswith('-'):
        return (number, 2)
    else:
        return (number, 1)

with that, the list sorts as required:

>>> sorted(my_list, key=plus_before_minus)
['1+', '1', '1-', '2+', '2', '2-']

Answer 2

Here, I am firstly creating a function get_priority to return the priority of each element. This returned number will be later used for sorting.

def get_priority(x):
    return {
        '+': 1,
        '-': 3
    }.get(x, 2)

# If returned number:
#     ends with '-': return 3 (Highest / First)
#     ends with '+': return 1 (Lowest / Last)
#     else: return 2 (Medium / Middle)

Then here I am going to use get_priority function along with itertools.groupby() , operator.itemgetter() and sorted() to achieve your desired order as:

from itertools import groupby
from operator import itemgetter

my_list = ['2', '1', '1+', '1-', '2+', '2-']

new_list = [i for _, l in groupby(sorted(my_list), key=itemgetter(0)) for i in sorted(l, key= lambda x: get_priority(x[-1]))]

where new_list will return you the value:

['1+', '1', '1-', '2+', '2', '2-']