custom sort in python, the built-in sorted()

let's say you have a list, and you want to sort it. you can use the build in function sorted()


Help on built-in function sorted in module __builtin__:

sorted(...)
    sorted(iterable, cmp=None, key=None, reverse=False) --> new sorted list
(END)

it takes any iterable as input.

for example:

>>> a=[4,2,1,6]

>>> sorted(a)

[1, 2, 4, 6]

>>> sorted(a, reverse=True)

[6, 4, 2, 1]

>>> a=['ccc','aaaa','d','bb']

>>> sorted(a)

['aaaa', 'bb', 'ccc', 'd']

if you want to sort according to the length of the string, pass a len function as the argument

>>> sorted(a, key=len)

['d', 'bb', 'ccc', 'aaaa']

>>> a=['ccc','aaaz','a','bb']

you want to sort according to the last letter of the string

>>> def last(s):

...     return s[-1]

... 

>>> sorted(a, key=last)

['a', 'bb', 'ccc', 'aaaz']

let's say you have a list of tuples, the sorted function sorts according to the first element 

of the tuple, if they are the same, compare the second element of the tuple.

>>> a=[(1,'b'),(2,'a'),(1,'a')]

>>> sorted(a)

[(1, 'a'), (1, 'b'), (2, 'a')]

so, if you want to sort by something first and then sort by another thing next, you can write

a key function to return a tuple.