Python dictionary sort about sort (), reversed (), sorted ()

First, the sort of python

1, reversed ()

This is very well understood,reversed English means:adj. reversed; reverse; (judgment, etc) revoked

Print List (Reversed ([' Dream ', ' a ', ' have ', ' I ')]) #[' i ', ' has ', ' a ', ' dream ']

2. Confusing sort () with sorted ()

In Python sorted is the built-in function (BIF), and sort () is the built-in function list.sort () of the list type.

Sorted ()

Sorted (iterable[, cmp[, key[, reverse]] )

Return A new sorted list from the items in iterable.

The optional arguments (optional parameter) CMP, key, and reverse with the same meaning as those for the  list.sort () &nbs P;method (described in section mutable Sequence Types).

CMP Specifies (specify) a custom comparison function of the arguments (iterable (iterative) elements) which should return a negativ E (plural), zero or positive (positive number) number depending on whether the first argument are considered smaller than, equal to, or larger than the second argument:  cmp=lambda x,y:cmp (X.lower (), Y.lower ()) . The default value is  None .

Key specifies a function of one argument that's used to extract a comparison key from each list element:  key= Str.lower . The default value is  None   (compare the elements directly).

Reverse is a Boolean value. If set to  True , then the list elements is sorted as if each comparison were reversed.

#字符串排序使用是字典序, rather than alphabetical order "" "sorted () sorted by dictionary order" "" lis = [' A ', ' C ', ' Z ', ' E ', ' T ', ' C ', ' B ', ' A ', ' good ', ' Tack ']print sorted (LIS)   #[' A ', ' C ', ' E ', ' good ', ' T ', ' Tack ', ' A ', ' B ', ' C ', ' Z ']

About Dictionary Ordering:

can refer to Baidu encyclopedia. Http://baike.baidu.com/view/4670107.htm

According to the ASCII row, the following:
0-9 (corresponds to the value 48-59);
A-Z (corresponds to the value 65-90);
A-Z (corresponds to the value 97-122);

------------

Standard order: Short in front, long in the back, and so on in turn than the letter,
such as to < up < Caps < Cat < too < <boat < boot < card

such as boat < boot <cap < card < Cat < to < too<, < up

What's more, dictionary order is the sort of dictionary, like a dictionary. I have not found the authority of the instructions, what is the dictionary order???? Ask for answers!!

Sort ()

S.sort ([cmp[, key[, reverse]])

Third, the dictionary sort of Python

1. Some features of the Python dictionary

Disordered:

Dictionary, shaped like dic = {' A ': 1, ' B ': 2, ' C ': 3}, the elements in the dictionary are not in order, so dic[0] is syntactically incorrect.

No weight:

There can be no duplicate key value, so dic.add[' c ' = 4, the dictionary becomes {' A ': 1, ' B ': 2, ' C ': 4}.

2. Sorting in different order according to "key" or "key value"

Function prototype: sorted (Dic,value,reverse)

Explanation:dic is a comparison function, value is a sorted object (this refers to a key or a key value),

Reverse: Indicate ascending or descending, true--descending, false--ascending (default)

3. Example:

DIC = {' A ': +, ' BC ': 5, ' C ': 3, ' ASD ': 4, ' + ': +, ' d ': 0}
The value of DIC is to be sorted from the big to the small (value is an integer).

DIC = {' A ': +, ' BC ': 5, ' C ': 3, ' ASD ': 4, ' + ': 0}print sorted (Dic.iteritems (), Key=lambda d:d[1], reverse = False) 
   #[(' d ', 0), (' C ', 3), (' ASD ', 4), (' BC ', 5), (' A ', 31), (' 33 ', 56)]

The explanations are as follows:

(1), Dic.iteritems (), returns the Ganso collection of dictionary key-value pairs

Print Dic.iteritems ()   #<dictionary-itemiterator object at 0x00b71a80>for obj in Dic.iteritems ():    print OBJ,OBJ[0],OBJ[1]    # (' A ', ' + ') a 31# (' C ', 3) C 3# (' d ', 0) d 0# (' BC ', 5) BC AA (' @ ', ' 4 ') 56# (' ASD ', 4) ASD

(2), about sort objects

As mentioned above, value (or key) is a sorted object (this refers to a key or a key value), but why use a lambda function, see here: Click to read

Key=lambda D:d[1] is the sort object with the key value (value).

Key = Lambda d:d[1]for i in Dic.iteritems ():    print key (i),   #输出31 3 0 5 56 4, these are the values of the dictionary dic

If you select key = Lambda d:d[0], select Key key as the sort object.

(3), reverse

Reverse is reversed, reverse=ture represents reverse.

(4), note:

Sorted (Dic.iteritems (), Key=lambda d:d[1], reverse = False) Iterates the dic.iteritems of each of the Ganso () key-value pairs, each of which passes as a parameter to key () function (I'm talking about this: Key=lambda d:d[1],).

4. Review

Lis = [' A ', ' BC ', ' C ', ' ASD ', ']print ', ' d ' sorted (LIS)   #[', ' a ', ' ASD ', ' BC ', ' C ', ' d ']

Compare letters, such as boat < boot <cap < card < Cat < to < too< and < up

5. Questions

Examples can be found in: [**python's sorting function sort,sorted application in list sorting and dictionary sorting and Examples *] (http://wangwei007.blog.51cto.com/68019/1100742)

There is now a sort of sort in this case. such as the big question number sort, then the big question corresponding small question number also sorts, as follows:

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lis =[{‘Big‘:3, ‘small‘:2},{‘Big‘:3, ‘small‘:4},{‘Big‘:2, ‘small‘:2}, {‘Big‘:3, ‘small‘:1},{‘Big‘:2, ‘small‘:1},{‘Big‘:1, ‘small‘:1}]# 大题号排序li =sorted(lis, key=lambdas: s[‘Big‘])# 输出：#[{‘small‘: 1, ‘Big‘: 1}, {‘small‘: 2, ‘Big‘: 2}, {‘small‘: 1, ‘Big‘: 2}, {‘small‘: 2, ‘Big‘: 3}, {‘small‘: 4, ‘Big‘: 3}, {‘small‘: 1, ‘Big‘: 3}]# 小题号排序：sort_ff =[]no =set([i[‘Big‘] fori inli])forobj inno:li_ =[]for i inff:ifi[‘Big‘] ==obj:li_.append(i)l =sorted(li_, key=lambda s: s[‘small‘])forj inl:sort_ff.append(j)# 输出结果：[{‘small‘: 1, ‘Big‘: 1}, {‘small‘: 1, ‘Big‘: 2}, {‘small‘: 2, ‘Big‘: 2}, {‘small‘: 1, ‘Big‘: 3}, {‘small‘: 2, ‘Big‘: 3}, {‘small‘: 4, ‘Big‘: 3}]

Python dictionary sort about sort (), reversed (), sorted ()