Expand Up @@ -593,12 +593,58 @@ of the above sections. This flag causes mypy to suppress errors caused by not being able to fully infer the types of global and class variables.
.. option:: --allow-redefinition .. option:: --allow-redefinition-new
By default, mypy won't allow a variable to be redefined with an unrelated type. This flag enables redefinition of a variable with an unrelated type. This *experimental* flag enables the redefinition of unannotated variables with an arbitrary type. You will also need to enable :option:`--local-partial-types <mypy --local-partial-types>`. Example:
.. code-block:: python
def maybe_convert(n: int, b: bool) -> int | str: if b: x = str(n) # Assign "str" else: x = n # Assign "int" # Type of "x" is "int | str" here. return x
Without the new flag, mypy only supports inferring optional types (``X | None``) from multiple assignments. With this option enabled, mypy can infer arbitrary union types.
This also enables an unannotated variable to have different types in different code locations:
.. code-block:: python
if check(): for x in range(n): # Type of "x" is "int" here. ... else: for x in ['a', 'b']: # Type of "x" is "str" here. ...
Note: We are planning to turn this flag on by default in a future mypy release, along with :option:`--local-partial-types <mypy --local-partial-types>`. The feature is still experimental, and the semantics may still change.
.. option:: --allow-redefinition
This is an older variant of :option:`--allow-redefinition-new <mypy --allow-redefinition-new>`. This flag enables redefinition of a variable with an arbitrary type *in some contexts*: only redefinitions within the same block and nesting depth as the original definition are allowed.
We have no plans to remove this flag, but we expect that :option:`--allow-redefinition-new <mypy --allow-redefinition-new>` will replace this flag for new use cases eventually.
Example where this can be useful:
.. code-block:: python Expand Down