Query params MultiDict.getlist raises KeyError on missing key

[aalvrz]

@app.route('/')
def index():
    query_params = app.current_request.query_params
    stuff = query_params.getlist("stuff")  # KeyError if query param not passed in request

I believe that it makes sense that a behavior similar to using get (fall back to a value) is expected when using getlist.

[jamesls]

I went through the commit history, and it looks like the original version of getlist() worked the way you mention, it didn't raise a KeyError. That would be the behavior that I expect as well.

However, it looks like that was changed in #1165, and an explicit test was added for it. I'll need to track down why this was changed, I'm not seeing anything in the PR discussion.

However, at this point, changing it would introduce backwards incompatibilities for people that are already catching KeyError and handling missing keys that way.

[aalvrz]

@jamesls I am aware of the backward incompatibility, but handling the exception in the route for this kind of situation feels like polluting the route IMO. Is there any possibility of introducing this change? I am sure it will be preferred over handling KeyError despite the backwards incompatibility.