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I have two dictionaries.
a = {"ab":3, "bd":4}
b = {"cd":3, "ed":5}`
I want to combine them to {'bd': 4, 'ab': 3, 'ed': 5, 'cd': 3}.
As this says, a.update(b) can complete it. But when I try, I get:
type(a.update(b)) #--> type 'NoneType'
Would anyone like to explain it to me why I cannot gain a dict type?
I also tried this, and it did well:
type(dict(a,**b)) #-->type 'dict'
What is the difference between these two methods and why did the first one not work?
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The update() method inserts the specified items to the dictionary. The specified items can be a dictionary, or an iterable object with key value pairs.
The Python dictionary offers an update() method that allows us to append a dictionary to another dictionary. The update() method automatically overwrites the values of any existing keys with the new ones.
Python Dictionary update() Method It inserts key/value if it is not present. It updates key/value if it is already present in the dictionary. It also allows an iterable of key/value pairs to update the dictionary. like: update(a=10,b=20) etc.
Values of a Python Dictionary can be updated using the following two ways i.e. using the update() method and also, using square brackets. Dictionary represents the key-value pair in Python, enclosed in curly braces.
The update method updates a dict in-place. It returns None, just like list.extend does. To see the result, look at the dict that you updated.
>>> a = {"ab":3, "bd":4}
>>> b = {"cd":3, "ed":5}
>>> update_result = a.update(b)
>>> print(update_result)
None
>>> print(a)
{'ed': 5, 'ab': 3, 'bd': 4, 'cd': 3}
If you want the result to be a third, separate dictionary, you shouldn't be using update. Use something like dict(a, **b) instead, which, as you've already noticed, constructs a new dict from the two components, rather than updating one of the existing ones.
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