如何按升序对长列表进行排序

Question

                print(addition)
                decimal = sum(addition) / len(addition)
                d = decimal * 100
                percentage = float("{0:.2f}".format(d))
                print(percentage)
                list_name_second.append({'Name': x, 'percentage': float(percentage)})
                list_name.append(x)
                addition.clear()

    i = i + 1
if i == num_lines:
    def sort_percentages(list_name_second):
        print(list_name_second.sort('percentage'))

    print(sort_percentages(list_name_second), end='\n\n')

the code above is within a loop (apart from the bottom part) it collects percentages and stores then in a list that looks like this:

[{'Name': 'Malcolm', 'percentage': '50.0'}]

I want to be able to sort the list using the percentages but I don't know how to do this, please help

also the print functions within the calculations were for troubleshooting, dont pay attention to them

Answer 1

You can use python's built-in functions sort() or sorted() where sort() method will sort the list in-place, and sorted() will return a new sorted list in case you don't need the original list. both sort() and sorted() have a key parameter that specify a callable which will be called on each list's element for comparisons. for more details, see docs

if we say that your list for example look like this:

>>> list_name_second = [
    {'Name': 'Malcolm', 'percentage': 50.0},
    {'Name': 'Sam', 'percentage': 30.0},
    {'Name': 'Ru', 'percentage': 100.0},
    {'Name': 'Kam', 'percentage': 10.0},
    {'Name': 'Joe', 'percentage': 20.0}
   ]

so, you can sort your list in-place based on percentage key of dict list element using sort(key=callable) like follows:

>>> list_name_second.sort(key=lambda d: d['percentage'])
>>> list_name_second
[{'Name': 'Kam', 'percentage': 10.0}, {'Name': 'Joe', 'percentage': 20.0}, {'Name': 'Sam', 'percentage': 30.0}, {'Name': 'Malcolm', 'percentage': 50.0}, {'Name': 'Ru', 'percentage': 100.0}]

or, you can use sorted(key=callable) which it will return a new sorted list, like follows:

>>> sorted(list_name_second, key=lambda d: d['percentage'])
[{'Name': 'Kam', 'percentage': 10.0}, {'Name': 'Joe', 'percentage': 20.0}, {'Name': 'Sam', 'percentage': 30.0}, {'Name': 'Malcolm', 'percentage': 50.0}, {'Name': 'Ru', 'percentage': 100.0}]

here, you are passing a callable lambda function to be applied on each element of the list, which its extract the 'percentage' key's value from the dict and return it to sort or sorted built-in functions to be used as reference for sorting process.

Note: if your elements in the list look like this: [{'Name': 'Malcolm', 'percentage': '50.0'}] , where 'percentage' 's value is a string, you have to cast its value to compared as a float, like this:

>>> list_name_second = [
    {'Name': 'Malcolm', 'percentage': '50.0'},
    {'Name': 'Sam', 'percentage': '30.0'},
    {'Name': 'Ru', 'percentage': '100.0'},
    {'Name': 'Kam', 'percentage': '10.0'},
    {'Name': 'Joe', 'percentage': '20.0'}
    ]
>>> sorted(list_name_second, key=lambda d: float(d['percentage']))
[{'Name': 'Kam', 'percentage': '10.0'}, {'Name': 'Joe', 'percentage': '20.0'}, {'Name': 'Sam', 'percentage': '30.0'}, {'Name': 'Malcolm', 'percentage': '50.0'}, {'Name': 'Ru', 'percentage': '100.0'}]