Detailed explanation of how to sort dictionary elements in a list using Python programming

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Content directory:

1. Origin of the problem
2. Sorting dictionary elements in the list
3. Compare json (ignoring the order of the dictionaries in the list)

1. Origin of the problem

##json

Objecta,b

a = '{"ROAD": [{"id": 123}, {"name": "no1"}]}'
b = '{"ROAD": [{"name": "no1"}, {"id": 123}]}'

Features: The key values ​​corresponding to the keys in the Python objects corresponding to a and b - the lists contain the same dictionary elements , but the only difference is the order. How to tell if two json are equal if order is ignored. Because the dictionary itself sorts itself by key and the list is sorted in the order of joining, it can be easily sorted if you sort the dictionary elements in the list. If the list contains ordinary elements (not a dictionary), the list can be read and sorted through the

list(set()) combination. However, if the list contains dictionary elements, list(set cannot be used) ()) combination, see the prompt:

>>> a = [{'a':1, 'b':2}, {'c':3}]
>>> a
[{'a': 1, 'b': 2}, {'c': 3}]
>>> b = set(a)
Traceback (most recent call last):
 File "<pyshell#2>", line 1, in <module>
  b = set(a)
TypeError: unhashable type: &#39;dict&#39;

The prompt is that the dictionary is a type that cannot be hashed (ordinary non-dictionary elements can be easily arranged by hashing) sequence).

Then the essence of the problem is: how to sort the dictionary elements in the list.

2. Sort the dictionary elements in the list

Fortunately, the list has the

sorted function , try it

>>> p = [{'b': 2}, {'a': 1, 'c': 3}]
>>> q = [{'a': 1, 'c': 3}, {'b': 2}]
>>> p
[{'b': 2}, {'a': 1, 'c': 3}]
>>> q
[{'a': 1, 'c': 3}, {'b': 2}]
>>> pp = sorted(p)
>>> qq = sorted(q)
>>> pp
[{'b': 2}, {'a': 1, 'c': 3}]
>>> qq
[{'b': 2}, {'a': 1, 'c': 3}]
>>> pp == qq
True
>>> p == q
False

You can see that it is ok, and you can see that the principle of sorting is the number of elements.

3. Compare json (ignoring the order of dictionaries in the list)

import json
def compare_json(a, b):
  aa = json.loads(a)
  bb = json.loads(b)
  len_a = len(aa)
  len_b = len(bb)
  if len_a != len_b:
    return False
  else:
    for key in aa:
      if not bb.has_key(key):
        return False
      else:
        if sorted(aa[key]) != sorted(bb[key]):
          return False
  return True
if name == "main":
  a = '{"ROAD": [{"id": 123}, {"name": "no1"}]}'
  b = '{"ROAD": [{"name": "no1"}, {"id": 123}]}'
  print compare_json(a, b)

Details: When writing the json format yourself, a = "{'road':1}" json.loads(a) is wrong, you have to write it as a = '{"road:1}' [Single quotation marks are excluded]

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