Do Python Dictionaries Guarantee Ordered Key-Value Retrieval with `keys()` and `values()`?

Do Python Dictionary's Keys and Values Maintain Constant Ordering?

In Python, dictionaries are collections of key-value pairs, where keys are unique and used as identifiers for their corresponding values. Accessing a dictionary's keys and values using the keys() and values() methods is a common operation. However, a question arises: are the order of keys and values always consistent when these methods are invoked sequentially?

Response

According to the official Python documentation, if no modifications are made to a dictionary between calling keys() and values(), the order of the returned lists will correspond directly. This means that for each index in the keys list, the corresponding value can be found at the same index in the values list.

Here's an example:

d = {'one': 1, 'two': 2, 'three': 3}
k, v = d.keys(), d.values()

for i in range(len(k)):
    print("{}: {}".format(k[i], v[i]))  # Prints keys and corresponding values

# Result:
# one: 1
# two: 2
# three: 3

The documentation states this correspondence explicitly:

If items(), keys(), values(), iteritems(), iterkeys(), and itervalues() are called with no intervening modifications to the dictionary, the lists will directly correspond.

Conclusion

As long as the dictionary remains unchanged, the keys() and values() methods return lists that maintain a consistent ordering, enabling easy mapping of keys to their corresponding values. This behavior is explicitly documented and ensures reliable usage in Python code.

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