如何取得 Python 3 中的字典鍵列表？

Retrieving Dictionary Keys as List in Python

In Python 2.7, obtaining a list of dictionary keys is straightforward:

newdict = {1:0, 2:0, 3:0}
newdict.keys()

However, in Python 3.3 onwards, the output is a "dict_keys" object, not a list:

newdict.keys()

This article explores how to obtain a plain list of keys in Python 3.

Converting dict_keys to List

To convert the dict_keys object to a list, use list comprehension:

list(newdict.keys())

This will produce a list of keys:

[1, 2, 3]

Duck Typing Consideration

However, it's important to consider if converting to a list is necessary. Pythonic principles encourage "duck typing," where objects can be treated as their intended type if they exhibit the correct behavior. In this case, dict_keys can be iterated over like a list:

for key in newdict.keys():
    print(key)

This code will iterate through the keys and print them one by one.

Insertion Considerations

Note that dict_keys does not support insertions, so the following code will not work:

newdict.keys()[0] = 10  # Will result in TypeError

If you require insertion functionality, you should use a list instead of dict_keys.

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