How Can I Avoid Shared References When Using Python's `fromkeys` Method?

Understanding the fromkeys Method and its Limitations

When initializing a dictionary using the fromkeys method, it is important to be aware of its behavior with single-element arguments. Passing a list as the second argument will result in all dictionary values referencing the same list object.

Avoiding Unintended Sharing: Alternative Approaches

To prevent unintended sharing of values, consider using alternative methods:

• Dict Comprehension (Python 2.7 ):

  data = {k: [] for k in range(2)}

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• List Comprehension with Dict Constructor:

  data = dict([(k, []) for k in range(2)])

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• Generator Expression with Dict (Python 2.4-2.6):

  data = dict((k, []) for k in range(2))

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Simple Example: Adding a Value to a Specific Key

The following code demonstrates the intended behavior:

data = {0: [], 1: []}
data[1].append('hello')
print(data)
# Output: {0: [], 1: ['hello']}

By using one of the suggested methods, you can initialize a dictionary of empty lists and modify individual key values without affecting the others.

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