I am trying to understand mypy a little better. For the following line of code:
request_body: dict = {}
request_body = request.get_json()
mypy returns an error:
error: Incompatible types in assignment (expression has type "Optional[Any]", variable has type "Dict[Any, Any]")
What is the correct fix for this?
As you can see in the following code, taken from /wekzeug/wrappers/request.py, the function get_json
doesn't always return a dictionary. I would suggest removing the type hinting from the variable, as it can be None or a dictionary.
def get_json(
self, force: bool = False, silent: bool = False, cache: bool = True
) -> t.Optional[t.Any]:
"""Parse :attr:`data` as JSON.
If the mimetype does not indicate JSON
(:mimetype:`application/json`, see :meth:`is_json`), this
returns ``None``.
If parsing fails, :meth:`on_json_loading_failed` is called and
its return value is used as the return value.
:param force: Ignore the mimetype and always try to parse JSON.
:param silent: Silence parsing errors and return ``None``
instead.
:param cache: Store the parsed JSON to return for subsequent
calls.
"""
if cache and self._cached_json[silent] is not Ellipsis:
return self._cached_json[silent]
if not (force or self.is_json):
return None
data = self.get_data(cache=cache)
try:
rv = self.json_module.loads(data)
except ValueError as e:
if silent:
rv = None
if cache:
normal_rv, _ = self._cached_json
self._cached_json = (normal_rv, rv)
else:
rv = self.on_json_loading_failed(e)
if cache:
_, silent_rv = self._cached_json
self._cached_json = (rv, silent_rv)
else:
if cache:
self._cached_json = (rv, rv)
return rv
This line specifically causes the method to return None:
except ValueError as e:
if silent:
rv = None