One can create dictionaries using generators (PEP-289):
dict((h,h*2) for h in range(5))
#{0: 0, 1: 2, 2: 4, 3: 6, 4: 8}
Is it syntactically possible to add some extra key-value pairs in the same dict() call? The following syntax is incorrect but better explains my question:
dict((h,h*2) for h in range(5), {'foo':'bar'})
#SyntaxError: Generator expression must be parenthesized if not sole argument
In other words, is it possible to build the following in a single dict() call:
{0: 0, 1: 2, 2: 4, 3: 6, 4: 8, 'foo': 'bar' }
In Python, we can add multiple key-value pairs to an existing dictionary. This is achieved by using the update() method. This method takes an argument of type dict or any iterable that has the length of two - like ((key1, value1),) , and updates the dictionary with new key-value pairs.
As we can see, dict() is obviously slower than {}. Especially, if the dictionary is initialized with many elements, it has a huge impact if your code needs 0.04ms or almost 0.08ms to create your dictionary. Even when you initialize an empty dictionary, it is slower.
Python Dictionary keys() method The keys() method in Python Dictionary, returns a view object that displays a list of all the keys in the dictionary in order of insertion using Python. Parameters: There are no parameters. Returns: A view object is returned that displays all the keys.
In python, if we want a dictionary in which one key has multiple values, then we need to associate an object with each key as value. This value object should be capable of having various values inside it. We can either use a tuple or a list as a value in the dictionary to associate multiple values with a key.
Constructor:
dict(iterableOfKeyValuePairs, **dictOfKeyValuePairs)
Example:
>>> dict(((h,h*2) for h in range(5)), foo='foo', **{'bar':'bar'})
{0: 0, 1: 2, 2: 4, 3: 6, 4: 8, 'foo': 'foo', 'bar': 'bar'}
(Note that you will need to parenthesize generator expressions if not the sole argument.)
dict([(h,h*2) for h in range(5)] + [(h,h2) for h,h2 in {'foo':'bar'}.items()])
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