[python] list.sort and sorted

1. sorted and list.sort

Python lists have a built-in list.sort() method that modifies the list in-place. There is also a sorted() built-in function that builds a new sorted list from an iterable.

• sorted accept any interable.
• list.sort() is only defined for list

Note that list.sort() will change the original list. If you will use the original list again, please use sorted. But if you will not use the original list, list.sort() is more efficient

1. sorted

Useage of sorted:
sorted(iterable[, cmp[, key[, reverse]]]) --> new sorted list

• iterable: return a new sorted list from the items in iterable.

  • any type of sequence: list, str, tuple…
  • some type of non-sequence: dict, file…
  • any object defined using _iter_ or _getitem_

• cmp: specifies a custom comparison function of two arguments (iterable elements), which should return a negative, zero or positive number depending on whether the first argument is considered smaller than, equal to, or larger than the second argument: cmp=lambda x,y: cmp(x.lower(), y.lower()).

• key: specifies a function of one argument that is used to extract a comparison key from each list element: key=str.lower.
• reverse: default = false, which means sorting increasingly.

2.1 sorted list

Example:

>>> mylist = [1,4,2,6,5]
>>> newlist1 = sorted(mylist)
>>> newlist1
[1, 2, 4, 5, 6]
>>> mylist
[1, 4, 2, 6, 5]
>>> newlist2 = sorted(mylist, reverse=True)
>>> newlist2
[6, 5, 4, 2, 1]

2.2 sorted dictionary

Common usage:

• sorted(dict.items(), key=lambda e:e[1], reverse=True) where eis an element of dict.items(). ```e[0]` means sorting by key ande[1]“ means sorting by value.

# use key
>>> mydict = {"Lucy":11, "Lily":16, "LiMei":9}
>>> sorted(mydict.items(), key=lambda e:e[1])# sort by value
[('LiMei', 9), ('Lucy', 11), ('Lily', 16)]
#　use cmp
>>> sorted(mydict.items(), cmp=lambda x,y: cmp(x[1],y[1]))# sort by value
[('LiMei', 9), ('Lucy', 11), ('Lily', 16)]

We can use operator to make sort faster.
import operator
- operator.itemgetter(1)

# use operator
>>> sorted(mydict.items(), key=operator.itemgetter(1))
[('LiMei', 9), ('Lucy', 11), ('Lily', 16)]

Note: return a list of tuple because mylist.items()gives a list of tuples.

2. list.sort()

Example:

>>> mylist = [1,4,2,6,5]
>>> mylist.sort()
>>> mylist
[1, 2, 4, 5, 6]

Note original list changed