Stronger typing for request.headers.get method

[pcorpet]

Since v2 and the typing stubs, the get method of the Headers data structure always returns a Optional[str]. However in some cases we can know statically that it will return a str. Indeed when a default string parameter is given, then the function always return a str.

Here's a preview of my code before v2:

auth_token = flask.request.headers.get('Authorization', '').replace('Bearer ', '')

Now that werkzeug is typed, the .replace will raise an typing error when analyzed with mypy.

error: Item "None" of "Optional[str]" has no attribute "replace"

I can fix it like this:

auth_token = typing.cast(str, flask.request.headers.get('Authorization', '')).replace('Bearer ', '')

or even like this

auth_header = flask.request.headers.get('Authorization', '')
if auth_header:
  auth_token = auth_header.replace('Bearer ', '')
else:
  auth_token = ''

But I feel like all of those patches shouldn't be required. I'll send a type fix.

[ThiefMaster]

I guess we need an @overload definition for get and similar methods... like here: https://github.com/python/typeshed/blob/a7302dc6cb9527ba8cb014327e29c035d991550f/stdlib/typing.pyi#L443-L446