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I have 5 dictionaries and I want a union of their keys.
alldict = [dict1, dict2, dict3, dict4, dict5]
I tried
allkey = reduce(lambda x, y: set(x.keys()).union(y.keys()), alldict)
but it gave me an error
AttributeError: 'set' object has no attribute 'keys'
Am I doing it wrong ? I using normal forloop but I wonder why the above code didn't work.
929
Use *args to take multiple arguments. Show activity on this post. Show activity on this post. If you want to avoid combining the dictionaries, then provide them as arguments rather than keyword arguments, and set their defaults to something (such as None ), and convert None to {} and otherwise copy the dictionary.
In the latest update of python now we can use “|” operator to merge two dictionaries. It is a very convenient method to merge dictionaries.
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.
I think @chuck already answered the question why it doesn't work, but a simpler way to do this would be to remember that the union method can take multiple arguments:
allkey = set().union(*alldict)
does what you want without any loops or lambdas.
140
Your solution works for the first two elements in the list, but then dict1 and dict2 got reduced into a set and that set is put into your lambda as the x. So now x does not have the method keys() anymore.
The solution is to make x be a set from the very beginning by initializing the reduction with an empty set (which happens to be the neutral element of the union).
Try it with an initializer:
allkey = reduce(lambda x, y: x.union(y.keys()), alldict, set())
An alternative without any lambdas would be:
allkey = reduce(set.union, map(set, map(dict.keys, alldict)))
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