Adding dictionaries in lists using heappush-CodePudding

I've been trying to add dictionaries to a list using the heappush function. The first heappush statement works fine, and the print statement after that is executed.

#random tests
node1 = {'a':1, 'b':2, 'c':3}
node2 = {'c':4, 'd':5, 'e':6}
lists = []
heappush(lists, node1)
print(lists)
heappush(lists, node2)

However, when I try to execute the second heappush statement, it gives me the following error.

[{'a': 1, 'b': 2, 'c': 3}]
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-24-c680e53f9699> in <module>()
      5 heappush(lists, node1)
      6 print(lists)
----> 7 heappush(lists, node2)

TypeError: '<' not supported between instances of 'dict' and 'dict'

Why is that? I know I can use append function to append dictionaries to the list, but I want to use heappush instead

CodePudding user response：

The heap data structure stores the elements in the list in a specific format, so that the pop() and push() functions are both O(log n). When putting a new element in the heap, we need to compare it with the other objects in the heap to determine position of the new item in the list, which is done using the comparison operators <.

Python dicts don't have comparison operators defined to decide which dict is smaller/larger than the other. What is your use case for putting dicts into a heap? If you want to have some kind of sorted order with dicts you will need to define the comparator methods for the dict on your own.