ItemsView behavior about multidict

[webknjaz]

There's MultiDict.getall(key, default=_marker) for pulling all key's values.

Getting a single value by its key should remain the same regardless of how many times you called it.

[asvetlov]

Also you could iterate over key/value pairs:

In [3]: d = MultiDict([('1', 'foo'), ('2', 'bar'), ('1', 'baz')])

In [4]: for k, v in d.items():
   ...:     print(k, v)
   ...:     
1 foo
2 bar
1 baz

__getitem__ is and alias for getone() which returns a first found value.

[asvetlov]

Internally multidict is a sequence of key/value pairs.
This is very important: HTTP headers are ordered and sometimes, in very rare cases, it is crucial.
The order should be not changed after serializing headers back.

[akhomchenko]

I know about items and getall. Just wanted to clarify that you are aware of this behavior. Thank you a lot.

Offtopic question not to raise another issue:
Is it crucial to have an order not changed only for a specific header or for a sequence of headers also?

I just want to understand if it makes sense trying to implement it on top of regular dicts. With OrderedDict prior python 3.6 and regular dict on 3.6 we can achieve order for values for a specific header, but not for a headers themselves. I've seen #68 (comment)

[asvetlov]

Yes, I understand.
It's a subtle matter but for example Forwarded and X-Forwarded-* headers might overlap.
I thought about keeping order for values inside a key only.
Moreover early multidict implementations was built in this way.
But later I've switched to linear key-value pairs sequence because people was confused at least.

[webknjaz]

@gagoman I consider the question answered. Feel free to reopen it if you have any further questions.