Why do dict1.items() <= dict2.items() and dict1.viewitems() <= dict2.viewitems() return different results?

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I am confused as to why .items() returns a different result than .viewitems() when comparing two dictionaries as a list.

# python 2.7
d1 = {'1': '10', '2': '20'}  # two key-value pairs
d2 = {'3': '30', '4': '40', '5': '50'}  # three key-value pairs
print d1 <= d2  # True
print d1.items() <= d2.items()  # True
print d1.viewitems() <= d2.viewitems()  # False
print d1.items()  # [('1', '10'), ('2', '20')]
print d1.viewitems()  # dict_items([('1', '10'), ('2', '20')])

Seems like the main difference between .items() and .viewitems() is that .items() returns a list and viewitems() returns a dict_items thingy.

Is it recommended to just use d1 <= d2 rather than viewitems or items when comparing the size between dictionaries?

Also, how to make this compatible with Python 3?


d1 <= d2  # True

It's complicated. And it's implementation detail. See What do comparison operators do on dictionaries? TL;DR: a shorter dictionary is always smaller than a longer one in Python 2.x, but dicts are not orderable at all in Python 3.x.

d1.items() <= d2.items()  # True

This is a lexicographical comparison of lists. That True result is reliable, since every key in d1 is less than any key of d2. To make this code cross-compatible, you would have to convert to list explicitly.

d1.viewitems() <= d2.viewitems()  # False

This is a subset-like check. That False result is reliable, because d1 is not a "subdict" of d2. To make this code cross-compatible, use six.viewitems or similar.

Is it recommended to just use d1 <= d2 rather than viewitems or items when comparing the size between dictionaries?

Neither, use len(d1) <= len(d2) to compare the size between dictionaries.

Python Dictionary items(), The syntax of items() method is: dictionary.items(). The items() method is similar to dictionary's viewitems() method in Python 2.7  dict1.items() dict_items([('c', 3), ('d', 4), ('a', 1), ('b', 2)]) This is the general template you can follow for dictionary comprehension in Python: dict_variable = {key:value for (key,value) in dictonary.items()} This can serve as the basic and the most simple template. This can get more and more complex as you add conditionalities to it.


I've answered a similar question here: Inconsistent behaviour between dict.values() and dict.keys() equality in Python 3.x and Python 2.7

The key thing to note is that dict.viewitems() is a Set-like object. Which means that when you do d1.viewitems() <= d2.viewitems() you are comparing checking if d1.viewitems() is a subset of d2.viewitems(), not the length comparison you expected. See the documentation here: https://docs.python.org/2.7/library/sets.html#set-objects

Operation         Equivalent  Result
s.issubset(t)     s <= t      test whether every element in s is in t
s.issuperset(t)   s >= t      test whether every element in t is in s

Note: because dict.viewitem() is a collections.Set object, it doesn't have .issubset or .issuperset methods like set does.

Observe the following:

>>> d1 = {'a': 0}
>>> d2 = {'a': 1}
>>> d3 = {'a': 0, 'b': 1}
>>> d1.viewitems() <= d3.viewitems()
True     # because [('a', 0)] is a subset of [('a', 0), ('b', 1)]
>>> d2.viewitems() <= d3.viewitems()
False    # because [('a', 1)] is not a subset of [('a', 0), ('b', 1)]

To answer your question though - as others have mentioned, to compare size, use len(d1) <= len(d2) instead.

Python for Developers: Learn to Develop Efficient Programs using , The question is when to use list(dict1.items()) and dict1.items(). Let us run a program: dict1 = {22: 'SSH', 23: 'Telnet', 53: 'DNS', 80: 'HTTP', 443: 'HTTPS'} for k,v​  In this article we will discuss how to add or append new key value pairs in a dictionary and also how to update value of existing keys. Python dictionary provides a member function update() i.e.


Your stated purpose is to compare dictionary sizes ... which you haven't done at all. You need to use len for that.

What you did do is comparing items of two very different types. items returns a list of tuples, which are easily compared by the well-known algorithms: check elements in the given order for relative value. Tuple comparison is familiar to most of us.

However, a dict_view is a dynamic view object, not a simple list of values. You're comparing a more complex object, not merely running down an obvious list of values. The ordering and comparison definition are not readily visible to us mere mortals.

Python Dictionary Comprehension Tutorial, dict1.items() dict_items([('c', 3), ('d', 4), ('a', 1), ('b', 2)]). This is the general template you can follow for dictionary comprehension in Python: What if we want to merged the contents of 2 or dictionaries to a new dictionary ? Let’s see how to do that. Merge two or more Dictionaries using **kwargs **kwargs. Using **kwargs we can send variable length key-value pairs to a function. When we apply ** to a dictionary, then it expands the contents in dictionary as a collection of key value


Learn Python in 7 Days, update() The syntax is given as: dict.update(dict2) dict2--this is the dictionary to by the keys of the dict1 dictionary. items() The syntax of the items() method is  Why Do Younger Black Voters Like Trump More Than Elders? Carrie Sheffield, Just the News June 11, 2020. AP Photo/Carolyn Kaster 'Because they're tired of hearing the same stories about victimhood


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