The `or` operator on dict.keys()

python, python-3.5, python-3.x

Solution

The Python 3 Documentation notes that the `dict.keys` method is set-like and implements `collections.abc.Set`.

Note that `dict.values` is not set-like even though it might appear to be so in your examples:

aonce = a.keys() | a.values()
bonce = b.keys() | b.values()

However these are leveraging off the fact that the keys view implements `__or__` (and `__ror__`) over arbitrary iterables.

For example, the following will not work:

>>> a.values() | b.values()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for |: 'dict_values' and 'dict_values'

Problem

As I've been unable to find any documentation on this, so I'll ask here. As shown in the code below, I found that the `or` operator (`|`), worked as such: ``` a = {"a": 1,"b": 2, 2: 3} b = {"d": 10, "e": 11, 11: 12} keys = a.keys() | b.keys() aonce = a.keys() | a.values() bonce = b.keys() | b.values() for i in keys: print(i, end=" ") print() for i in aonce: print(i, end=" ") print() for i in bonce: print(i, end=" ") print() ``` Which produces the result, in some order: ``` 2 d 11 a b e 3 1 2 a b 10 e 11 12 d ``` Initially I assumed these iterable was compatible with `|`, similar to the way sets are, however. Testing with other iterable, such as a `list.__iter__()`, threw an error. Even; ``` values = a.values() | b.values() for i in values: print(i, end=" ") print() ``` Which I'd assume worked, due to the use of `dict.values()` in the previous examples, threw an error. So, my question is; What on earth have I come across, and more importantly, how reliable is it? What subclass does my arguments need to be, for me to be able to use this?

Original source