docs/source/command_line.rst

.. _command-line:

.. program:: mypy

The mypy command line
=====================

This section documents mypy's command line interface. You can view
a quick summary of the available flags by running :option:`mypy --help`.

.. note::

   Command line flags are liable to change between releases.


Specifying what to type check
*****************************

By default, you can specify what code you want mypy to type check
by passing in the paths to what you want to have type checked::

    $ mypy foo.py bar.py some_directory

Note that directories are checked recursively.

Mypy also lets you specify what code to type check in several other
ways. A short summary of the relevant flags is included below:
for full details, see :ref:`running-mypy`.

.. option:: -m MODULE, --module MODULE

    Asks mypy to type check the provided module. This flag may be
    repeated multiple times.

    Mypy *will not* recursively type check any submodules of the provided
    module.

.. option:: -p PACKAGE, --package PACKAGE

    Asks mypy to type check the provided package. This flag may be
    repeated multiple times.

    Mypy *will* recursively type check any submodules of the provided
    package. This flag is identical to :option:`--module` apart from this
    behavior.

.. option:: -c PROGRAM_TEXT, --command PROGRAM_TEXT

    Asks mypy to type check the provided string as a program.


.. option:: --exclude

    A regular expression that matches file names, directory names and paths
    which mypy should ignore while recursively discovering files to check.
    Use forward slashes on all platforms.

    For instance, to avoid discovering any files named `setup.py` you could
    pass ``--exclude '/setup\.py$'``. Similarly, you can ignore discovering
    directories with a given name by e.g. ``--exclude /build/`` or
    those matching a subpath with ``--exclude /project/vendor/``. To ignore
    multiple files / directories / paths, you can provide the --exclude
    flag more than once, e.g ``--exclude '/setup\.py$' --exclude '/build/'``.

    Note that this flag only affects recursive directory tree discovery, that
    is, when mypy is discovering files within a directory tree or submodules of
    a package to check. If you pass a file or module explicitly it will still be
    checked. For instance, ``mypy --exclude '/setup.py$'
    but_still_check/setup.py``.

    In particular, ``--exclude`` does not affect mypy's discovery of files
    via :ref:`import following <follow-imports>`. You can use a per-module
    :confval:`ignore_errors` config option to silence errors from a given module,
    or a per-module :confval:`follow_imports` config option to additionally avoid
    mypy from following imports and checking code you do not wish to be checked.

    Note that mypy will never recursively discover files and directories named
    "site-packages", "node_modules" or "__pycache__", or those whose name starts
    with a period, exactly as ``--exclude
    '/(site-packages|node_modules|__pycache__|\..*)/$'`` would. Mypy will also
    never recursively discover files with extensions other than ``.py`` or
    ``.pyi``.

.. option:: --exclude-gitignore

    This flag will add everything that matches ``.gitignore`` file(s) to :option:`--exclude`.


Optional arguments
******************

.. option:: -h, --help

    Show help message and exit.

.. option:: -v, --verbose

    More verbose messages.

.. option:: -V, --version

    Show program's version number and exit.

.. option:: -O FORMAT, --output FORMAT {json}

    Set a custom output format.

.. _config-file-flag:

Config file
***********

.. option:: --config-file CONFIG_FILE

    This flag makes mypy read configuration settings from the given file.

    By default settings are read from ``mypy.ini``, ``.mypy.ini``, ``pyproject.toml``, or ``setup.cfg``
    in the current directory. Settings override mypy's built-in defaults and
    command line flags can override settings.

    Specifying :option:`--config-file= <--config-file>` (with no filename) will ignore *all*
    config files.

    See :ref:`config-file` for the syntax of configuration files.

.. option:: --warn-unused-configs

    This flag makes mypy warn about unused ``[mypy-<pattern>]`` config
    file sections.


.. _import-discovery:

Import discovery
****************

The following flags customize how exactly mypy discovers and follows
imports.

.. option:: --explicit-package-bases

    This flag tells mypy that top-level packages will be based in either the
    current directory, or a member of the ``MYPYPATH`` environment variable or
    :confval:`mypy_path` config option. This option is only useful
    in the absence of `__init__.py`. See :ref:`Mapping file
    paths to modules <mapping-paths-to-modules>` for details.

.. option:: --ignore-missing-imports

    This flag makes mypy ignore all missing imports. It is equivalent
    to adding ``# type: ignore`` comments to all unresolved imports
    within your codebase.

    Note that this flag does *not* suppress errors about missing names
    in successfully resolved modules. For example, if one has the
    following files::

        package/__init__.py
        package/mod.py

    Then mypy will generate the following errors with :option:`--ignore-missing-imports`:

    .. code-block:: python

        import package.unknown      # No error, ignored
        x = package.unknown.func()  # OK. 'func' is assumed to be of type 'Any'

        from package import unknown          # No error, ignored
        from package.mod import NonExisting  # Error: Module has no attribute 'NonExisting'

    For more details, see :ref:`ignore-missing-imports`.

.. option:: --follow-untyped-imports

    This flag makes mypy analyze imports from installed packages even if
    missing a :ref:`py.typed marker or stubs <installed-packages>`.

    .. warning::

        Note that analyzing all unannotated modules might result in issues
        when analyzing code not designed to be type checked and may significantly
        increase how long mypy takes to run.

.. option:: --follow-imports {normal,silent,skip,error}

    This flag adjusts how mypy follows imported modules that were not
    explicitly passed in via the command line.

    The default option is ``normal``: mypy will follow and type check
    all modules. For more information on what the other options do,
    see :ref:`Following imports <follow-imports>`.

.. option:: --python-executable EXECUTABLE

    This flag will have mypy collect type information from :pep:`561`
    compliant packages installed for the Python executable ``EXECUTABLE``.
    If not provided, mypy will use PEP 561 compliant packages installed for
    the Python executable running mypy.

    See :ref:`installed-packages` for more on making PEP 561 compliant packages.

.. option:: --no-site-packages

    This flag will disable searching for :pep:`561` compliant packages. This
    will also disable searching for a usable Python executable.

    Use this  flag if mypy cannot find a Python executable for the version of
    Python being checked, and you don't need to use PEP 561 typed packages.
    Otherwise, use :option:`--python-executable`.

.. option:: --no-silence-site-packages

    By default, mypy will suppress any error messages generated within :pep:`561`
    compliant packages. Adding this flag will disable this behavior.

.. option:: --fast-module-lookup

    The default logic used to scan through search paths to resolve imports has a
    quadratic worse-case behavior in some cases, which is for instance triggered
    by a large number of folders sharing a top-level namespace as in::

        foo/
            company/
                foo/
                    a.py
        bar/
            company/
                bar/
                    b.py
        baz/
            company/
                baz/
                    c.py
        ...

    If you are in this situation, you can enable an experimental fast path by
    setting the :option:`--fast-module-lookup` option.


.. option:: --no-namespace-packages

    This flag disables import discovery of namespace packages (see :pep:`420`).
    In particular, this prevents discovery of packages that don't have an
    ``__init__.py`` (or ``__init__.pyi``) file.

    This flag affects how mypy finds modules and packages explicitly passed on
    the command line. It also affects how mypy determines fully qualified module
    names for files passed on the command line. See :ref:`Mapping file paths to
    modules <mapping-paths-to-modules>` for details.


.. _platform-configuration:

Platform configuration
**********************

By default, mypy will assume that you intend to run your code using the same
operating system and Python version you are using to run mypy itself. The
following flags let you modify this behavior.

For more information on how to use these flags, see :ref:`version_and_platform_checks`.

.. option:: --python-version X.Y

    This flag will make mypy type check your code as if it were
    run under Python version X.Y. Without this option, mypy will default to using
    whatever version of Python is running mypy.

    This flag will attempt to find a Python executable of the corresponding
    version to search for :pep:`561` compliant packages. If you'd like to
    disable this, use the :option:`--no-site-packages` flag (see
    :ref:`import-discovery` for more details).

.. option:: --platform PLATFORM

    This flag will make mypy type check your code as if it were
    run under the given operating system. Without this option, mypy will
    default to using whatever operating system you are currently using.

    The ``PLATFORM`` parameter may be any string supported by
    :py:data:`sys.platform`.

.. _always-true:

.. option:: --always-true NAME

    This flag will treat all variables named ``NAME`` as
    compile-time constants that are always true.  This flag may
    be repeated.

.. option:: --always-false NAME

    This flag will treat all variables named ``NAME`` as
    compile-time constants that are always false.  This flag may
    be repeated.


.. _disallow-dynamic-typing:

Disallow dynamic typing
***********************

The ``Any`` type is used to represent a value that has a :ref:`dynamic type <dynamic-typing>`.
The ``--disallow-any`` family of flags will disallow various uses of the ``Any`` type in
a module -- this lets us strategically disallow the use of dynamic typing in a controlled way.

The following options are available:

.. option:: --disallow-any-unimported

    This flag disallows usage of types that come from unfollowed imports
    (such types become aliases for ``Any``). Unfollowed imports occur either
    when the imported module does not exist or when :option:`--follow-imports=skip <--follow-imports>`
    is set.

.. option:: --disallow-any-expr

    This flag disallows all expressions in the module that have type ``Any``.
    If an expression of type ``Any`` appears anywhere in the module
    mypy will output an error unless the expression is immediately
    used as an argument to :py:func:`~typing.cast` or assigned to a variable with an
    explicit type annotation.

    In addition, declaring a variable of type ``Any``
    or casting to type ``Any`` is not allowed. Note that calling functions
    that take parameters of type ``Any`` is still allowed.

.. option:: --disallow-any-decorated

    This flag disallows functions that have ``Any`` in their signature
    after decorator transformation.

.. option:: --disallow-any-explicit

    This flag disallows explicit ``Any`` in type positions such as type
    annotations and generic type parameters.

.. option:: --disallow-any-generics

    This flag disallows usage of generic types that do not specify explicit
    type parameters. For example, you can't use a bare ``x: list``. Instead, you
    must always write something like ``x: list[int]``.

.. option:: --disallow-subclassing-any

    This flag reports an error whenever a class subclasses a value of
    type ``Any``.  This may occur when the base class is imported from
    a module that doesn't exist (when using
    :option:`--ignore-missing-imports`) or is
    ignored due to :option:`--follow-imports=skip <--follow-imports>` or a
    ``# type: ignore`` comment on the ``import`` statement.

    Since the module is silenced, the imported class is given a type of ``Any``.
    By default mypy will assume that the subclass correctly inherited
    the base class even though that may not actually be the case.  This
    flag makes mypy raise an error instead.


.. _untyped-definitions-and-calls:

Untyped definitions and calls
*****************************

The following flags configure how mypy handles untyped function
definitions or calls.

.. option:: --disallow-untyped-calls

    This flag reports an error whenever a function with type annotations
    calls a function defined without annotations.

.. option:: --untyped-calls-exclude

    This flag allows one to selectively disable :option:`--disallow-untyped-calls`
    for functions and methods defined in specific packages, modules, or classes.
    Note that each exclude entry acts as a prefix. For example (assuming there
    are no type annotations for ``third_party_lib`` available):

    .. code-block:: python

        # mypy --disallow-untyped-calls
        #      --untyped-calls-exclude=third_party_lib.module_a
        #      --untyped-calls-exclude=foo.A
        from third_party_lib.module_a import some_func
        from third_party_lib.module_b import other_func
        import foo

        some_func()  # OK, function comes from module `third_party_lib.module_a`
        other_func()  # E: Call to untyped function "other_func" in typed context

        foo.A().meth()  # OK, method was defined in class `foo.A`
        foo.B().meth()  # E: Call to untyped function "meth" in typed context

        # file foo.py
        class A:
            def meth(self): pass
        class B:
            def meth(self): pass

.. option:: --disallow-untyped-defs

    This flag reports an error whenever it encounters a function definition
    without type annotations or with incomplete type annotations.
    (a superset of :option:`--disallow-incomplete-defs`).

    For example, it would report an error for :code:`def f(a, b)` and :code:`def f(a: int, b)`.

.. option:: --disallow-incomplete-defs

    This flag reports an error whenever it encounters a partly annotated
    function definition, while still allowing entirely unannotated definitions.

    For example, it would report an error for :code:`def f(a: int, b)` but not :code:`def f(a, b)`.

.. option:: --check-untyped-defs

    This flag is less severe than the previous two options -- it type checks
    the body of every function, regardless of whether it has type annotations.
    (By default the bodies of functions without annotations are not type
    checked.)

    It will assume all arguments have type ``Any`` and always infer ``Any``
    as the return type.

.. option:: --disallow-untyped-decorators

    This flag reports an error whenever a function with type annotations
    is decorated with a decorator without annotations.


.. _none-and-optional-handling:

None and Optional handling
**************************

The following flags adjust how mypy handles values of type ``None``.

.. _implicit-optional:

.. option:: --implicit-optional

    This flag causes mypy to treat parameters with a ``None``
    default value as having an implicit optional type (``T | None``).

    For example, if this flag is set, mypy would assume that the ``x``
    parameter is actually of type ``int | None`` in the code snippet below,
    since the default parameter is ``None``:

    .. code-block:: python

        def foo(x: int = None) -> None:
            print(x)

    **Note:** This was disabled by default starting in mypy 0.980.

.. _no_strict_optional:

.. option:: --no-strict-optional

    This flag effectively disables checking of optional
    types and ``None`` values. With this option, mypy doesn't
    generally check the use of ``None`` values -- it is treated
    as compatible with every type.

    .. warning::

        ``--no-strict-optional`` is evil. Avoid using it and definitely do
        not use it without understanding what it does.


.. _configuring-warnings:

Configuring warnings
********************

The following flags enable warnings for code that is sound but is
potentially problematic or redundant in some way.

.. option:: --warn-redundant-casts

    This flag will make mypy report an error whenever your code uses
    an unnecessary cast that can safely be removed.

.. option:: --warn-unused-ignores

    This flag will make mypy report an error whenever your code uses
    a ``# type: ignore`` comment on a line that is not actually
    generating an error message.

    This flag, along with the :option:`--warn-redundant-casts` flag, are both
    particularly useful when you are upgrading mypy. Previously,
    you may have needed to add casts or ``# type: ignore`` annotations
    to work around bugs in mypy or missing stubs for 3rd party libraries.

    These two flags let you discover cases where either workarounds are
    no longer necessary.

.. option:: --no-warn-no-return

    By default, mypy will generate errors when a function is missing
    return statements in some execution paths. The only exceptions
    are when:

    -   The function has a ``None`` or ``Any`` return type
    -   The function has an empty body and is marked as an abstract method,
        is in a protocol class, or is in a stub file
    -  The execution path can never return; for example, if an exception
        is always raised

    Passing in :option:`--no-warn-no-return` will disable these error
    messages in all cases.

.. option:: --warn-return-any

    This flag causes mypy to generate a warning when returning a value
    with type ``Any`` from a function declared with a non-``Any`` return type.

.. option:: --warn-unreachable

    This flag will make mypy report an error whenever it encounters
    code determined to be unreachable or redundant after performing type analysis.
    This can be a helpful way of detecting certain kinds of bugs in your code.

    For example, enabling this flag will make mypy report that the ``x > 7``
    check is redundant and that the ``else`` block below is unreachable.

    .. code-block:: python

        def process(x: int) -> None:
            # Error: Right operand of "or" is never evaluated
            if isinstance(x, int) or x > 7:
                # Error: Unsupported operand types for + ("int" and "str")
                print(x + "bad")
            else:
                # Error: 'Statement is unreachable' error
                print(x + "bad")

    To help prevent mypy from generating spurious warnings, the "Statement is
    unreachable" warning will be silenced in exactly three cases:

    1.  When the unreachable statement is a ``raise`` statement, is an
        ``assert False`` statement, or calls a function that has the :py:data:`~typing.NoReturn`
        return type hint. In other words, when the unreachable statement
        throws an error or terminates the program in some way.
    2.  When the unreachable statement is ``return NotImplemented``. This
        is allowed by mypy due to its use in operator overloading.
    3.  When the unreachable statement was *intentionally* marked as unreachable
        using :ref:`version_and_platform_checks`.

    .. note::

        Mypy currently cannot detect and report unreachable or redundant code
        inside any functions using :ref:`value-constrained type variables <value-constrained-type-variables>`.

        This limitation will be removed in future releases of mypy.

.. option:: --report-deprecated-as-note

    If error code ``deprecated`` is enabled, mypy emits errors if your code
    imports or uses deprecated features. This flag converts such errors to
    notes, causing mypy to eventually finish with a zero exit code. Features
    are considered deprecated when decorated with ``warnings.deprecated``.

.. option:: --deprecated-calls-exclude

    This flag allows one to selectively disable :ref:`deprecated<code-deprecated>` warnings
    for functions and methods defined in specific packages, modules, or classes.
    Note that each exclude entry acts as a prefix. For example (assuming ``foo.A.func`` is deprecated):

    .. code-block:: python

        # mypy --enable-error-code deprecated
        #      --deprecated-calls-exclude=foo.A
        import foo

        foo.A().func()  # OK, the deprecated warning is ignored

        # file foo.py
        from typing_extensions import deprecated
        class A:
            @deprecated("Use A.func2 instead")
            def func(self): pass

.. _miscellaneous-strictness-flags:

Miscellaneous strictness flags
******************************

This section documents any other flags that do not neatly fall under any
of the above sections.

.. option:: --allow-untyped-globals

    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

    By default, mypy won't allow a variable to be redefined with an
    unrelated type. This flag enables the redefinition of *unannotated*
    variables with an arbitrary type. This also requires
    :option:`--local-partial-types <mypy --no-local-partial-types>`, which is
    enabled by default starting from mypy 2.0. 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 this 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.
                ...

    Function arguments are special, changing their type within function body
    is allowed even if they are annotated, but that annotation is used to infer
    types of r.h.s. of all subsequent assignments. Such middle-ground semantics
    provides good balance for majority of common use cases. For example:

    .. code-block:: python

        def process(values: list[float]) -> None:
            if not values:
                values = [0, 0, 0]
            reveal_type(values)  # Revealed type is list[float]

    Note: We are planning to turn this flag on by default in a future mypy
    release.

.. option:: --allow-redefinition-new

    Deprecated alias for :option:`--allow-redefinition <mypy --allow-redefinition>`.

.. option:: --allow-redefinition-old

    This is an older, more limited variant of
    :option:`--allow-redefinition <mypy --allow-redefinition>`.
    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
    :option:`--allow-redefinition <mypy --allow-redefinition>`
    is recommended for new use cases.

    Example where this can be useful:

    .. code-block:: python

       def process(items: list[str]) -> None:
           # 'items' has type list[str]
           items = [item.split() for item in items]
           # 'items' now has type list[list[str]]

    The variable must be used before it can be redefined:

    .. code-block:: python

        def process(items: list[str]) -> None:
           items = "mypy"  # invalid redefinition to str because the variable hasn't been used yet
           print(items)
           items = "100"  # valid, items now has type str
           items = int(items)  # valid, items now has type int

.. option:: --no-local-partial-types

    Disable local partial types to enable legacy type inference mode for
    containers.

    Local partial types prevent inferring a container type for a variable, when
    the initial assignment happens at module top level or in a class body, and
    the container item type is only set in a function. Example:

    .. code-block:: python

        a = []  # Need type annotation unless using --no-local-partial-types

        def func() -> None:
            a.append(1)

        reveal_type(a)  # "list[int]" if using --no-local-partial-types

    Local partial types are enabled by default starting from mypy 2.0. The
    mypy daemon requires local partial types.

.. option:: --no-implicit-reexport

    By default, imported values to a module are treated as exported and mypy allows
    other modules to import them. This flag changes the behavior to not re-export unless
    the item is imported using from-as or is included in ``__all__``. Note this is
    always treated as enabled for stub files. For example:

    .. code-block:: python

       # This won't re-export the value
       from foo import bar

       # Neither will this
       from foo import bar as bang

       # This will re-export it as bar and allow other modules to import it
       from foo import bar as bar

       # This will also re-export bar
       from foo import bar
       __all__ = ['bar']


.. option:: --strict-equality

    By default, mypy allows always-false comparisons like ``42 == 'no'``.
    Use this flag to prohibit such comparisons of non-overlapping types, and
    similar identity and container checks:

    .. code-block:: python

       items: list[int]
       if 'some string' in items:  # Error: non-overlapping container check!
           ...

       text: str
       if text != b'other bytes':  # Error: non-overlapping equality check!
           ...

       assert text is not None  # OK, check against None is allowed


.. option:: --strict-equality-for-none

    This flag extends :option:`--strict-equality <mypy --strict-equality>` for checks
    against ``None``:

    .. code-block:: python

       text: str
       assert text is not None  # Error: non-overlapping identity check!

    Note that :option:`--strict-equality-for-none <mypy --strict-equality-for-none>`
    only works in combination with :option:`--strict-equality <mypy --strict-equality>`.

.. option:: --no-strict-bytes

    Treat ``bytearray`` and ``memoryview`` as subtypes of ``bytes``. This is not true
    at runtime and can lead to unexpected behavior. This was the default behavior prior
    to mypy 2.0.

    .. code-block:: python

       def f(buf: bytes) -> None:
           assert isinstance(buf, bytes)  # Raises runtime AssertionError with bytearray/memoryview
           with open("binary_file", "wb") as fp:
               fp.write(buf)

       # Using --no-strict-bytes disables the following errors
       f(bytearray(b""))  # Argument 1 to "f" has incompatible type "bytearray"; expected "bytes"
       f(memoryview(b""))  # Argument 1 to "f" has incompatible type "memoryview"; expected "bytes"

       # If `f` accepts any object that implements the buffer protocol,
       # consider using Buffer instead:
       from collections.abc import Buffer  # "from typing_extensions" in Python 3.11 and earlier

       def f(buf: Buffer) -> None:
           with open("binary_file", "wb") as fp:
               fp.write(buf)

       f(b"")  # Ok
       f(bytearray(b""))  # Ok
       f(memoryview(b""))  # Ok


.. option:: --extra-checks

    This flag enables additional checks that are technically correct but may be
    impractical. In particular, it prohibits partial overlap in ``TypedDict`` updates,
    and makes arguments prepended via ``Concatenate`` positional-only. For example:

    .. code-block:: python

       from typing import TypedDict

       class Foo(TypedDict):
           a: int

       class Bar(TypedDict):
           a: int
           b: int

       def test(foo: Foo, bar: Bar) -> None:
           # This is technically unsafe since foo can have a subtype of Foo at
           # runtime, where type of key "b" is incompatible with int, see below
           bar.update(foo)

       class Bad(Foo):
           b: str
       bad: Bad = {"a": 0, "b": "no"}
       test(bad, bar)

    In future more checks may be added to this flag if:

    * The corresponding use cases are rare, thus not justifying a dedicated
      strictness flag.

    * The new check cannot be supported as an opt-in error code.

.. option:: --strict

    This flag mode enables a defined subset of optional error-checking flags.
    This subset primarily includes checks for inadvertent type unsoundness (i.e
    strict will catch type errors as long as intentional methods like type ignore
    or casting were not used.)

    Note: the :option:`--warn-unreachable` flag
    is not automatically enabled by the strict flag.

    The strict flag does not take precedence over other strict-related flags.
    Directly specifying a flag of alternate behavior will override the
    behavior of strict, regardless of the order in which they are passed.
    You can see the list of flags enabled by strict mode in the full
    :option:`mypy --help` output.

    Note: the exact list of flags enabled by running :option:`--strict` may change
    over time.

    .. include:: strict_list.rst
    ..
        The above file is autogenerated and included during html generation.
        (That's an include directive, and this is a comment.)
        It would be fine to generate it at some other time instead,
        theoretically, but we already had a convenient hook during html gen.


.. option:: --disable-error-code

    This flag allows disabling one or multiple error codes globally.
    See :ref:`error-codes` for more information.

    .. code-block:: python

        # no flag
        x = 'a string'
        x.trim()  # error: "str" has no attribute "trim"  [attr-defined]

        # When using --disable-error-code attr-defined
        x = 'a string'
        x.trim()

.. option:: --enable-error-code

    This flag allows enabling one or multiple error codes globally.
    See :ref:`error-codes` for more information.

    Note: This flag will override disabled error codes from the
    :option:`--disable-error-code <mypy --disable-error-code>` flag.

    .. code-block:: python

        # When using --disable-error-code attr-defined
        x = 'a string'
        x.trim()

        # --disable-error-code attr-defined --enable-error-code attr-defined
        x = 'a string'
        x.trim()  # error: "str" has no attribute "trim"  [attr-defined]


.. _configuring-error-messages:

Configuring error messages
**************************

The following flags let you adjust how much detail mypy displays
in error messages.

.. option:: --show-error-context

    This flag will precede all errors with "note" messages explaining the
    context of the error. For example, consider the following program:

    .. code-block:: python

        class Test:
            def foo(self, x: int) -> int:
                return x + "bar"

    Mypy normally displays an error message that looks like this::

        main.py:3: error: Unsupported operand types for + ("int" and "str")

    If we enable this flag, the error message now looks like this::

        main.py: note: In member "foo" of class "Test":
        main.py:3: error: Unsupported operand types for + ("int" and "str")

.. option:: --show-column-numbers

    This flag will add column offsets to error messages.
    For example, the following indicates an error in line 12, column 9
    (note that column offsets are 0-based)::

        main.py:12:9: error: Unsupported operand types for / ("int" and "str")

.. option:: --show-error-code-links

    This flag will also display a link to error code documentation, anchored to the error code reported by mypy.
    The corresponding error code will be highlighted within the documentation page.
    If we enable this flag, the error message now looks like this::

        main.py:3: error: Unsupported operand types for - ("int" and "str")  [operator]
        main.py:3: note: See 'https://mypy.rtfd.io/en/stable/_refs.html#code-operator' for more info



.. option:: --show-error-end

    This flag will make mypy show not just that start position where
    an error was detected, but also the end position of the relevant expression.
    This way various tools can easily highlight the whole error span. The format is
    ``file:line:column:end_line:end_column``. This option implies
    ``--show-column-numbers``.

.. option:: --hide-error-codes

    This flag will hide the error code ``[<code>]`` from error messages. By default, the error
    code is shown after each error message::

        prog.py:1: error: "str" has no attribute "trim"  [attr-defined]

    See :ref:`error-codes` for more information.

.. option:: --pretty

    Use visually nicer output in error messages: use soft word wrap,
    show source code snippets, and show error location markers.

.. option:: --no-color-output

    This flag will disable color output in error messages, enabled by default.

.. option:: --no-error-summary

    This flag will disable error summary. By default mypy shows a summary line
    including total number of errors, number of files with errors, and number
    of files checked.

.. option:: --show-absolute-path

    Show absolute paths to files.

.. option:: --soft-error-limit N

    This flag will adjust the limit after which mypy will (sometimes)
    disable reporting most additional errors. The limit only applies
    if it seems likely that most of the remaining errors will not be
    useful or they may be overly noisy. If ``N`` is negative, there is
    no limit. The default limit is -1.


.. _incremental:

Incremental mode
****************

By default, mypy will store type information into a cache. Mypy
will use this information to avoid unnecessary recomputation when
it type checks your code again.  This can help speed up the type
checking process, especially when most parts of your program have
not changed since the previous mypy run.

If you want to speed up how long it takes to recheck your code
beyond what incremental mode can offer, try running mypy in
:ref:`daemon mode <mypy_daemon>`.

.. option:: --no-incremental

    This flag disables incremental mode: mypy will no longer reference
    the cache when re-run.

    Note that mypy will still write out to the cache even when
    incremental mode is disabled: see the :option:`--cache-dir` flag below
    for more details.

.. option:: --cache-dir DIR

    By default, mypy stores all cache data inside of a folder named
    ``.mypy_cache`` in the current directory. This flag lets you
    change this folder. This flag can also be useful for controlling
    cache use when using :ref:`remote caching <remote-cache>`.

    This setting will override the ``MYPY_CACHE_DIR`` environment
    variable if it is set.

    Mypy will also always write to the cache even when incremental
    mode is disabled so it can "warm up" the cache. To disable
    writing to the cache, use ``--cache-dir=/dev/null`` (UNIX)
    or ``--cache-dir=nul`` (Windows).

.. option:: --no-sqlite-cache

    Avoid using `SQLite`_ database to store the cache, instead write cache data
    out to individual files.

.. option:: --cache-fine-grained

    Include fine-grained dependency information in the cache for the mypy daemon.

.. option:: --skip-version-check

    By default, mypy will ignore cache data generated by a different
    version of mypy. This flag disables that behavior.

.. option:: --skip-cache-mtime-checks

    Skip cache internal consistency checks based on mtime.


.. _parallel:

Parallel type-checking
**********************

By default, mypy checks all modules in the same Python process. This can be slow
for large code bases. Mypy offers parallel type-checking mode using
multiple worker processes. In parallel mode, modules that do not depend om each
other are type-checked in parallel. :ref:`Incremental cache <incremental>` is
used to manage most of the shared state. Parallel type-checking also requires
:option:`--local-partial-types <mypy --no-local-partial-types>`, which is
enabled by default starting from mypy 2.0.

.. option:: -n VALUE, --num-workers VALUE

    Use the specified amount of parallel worker processes (in addition to the
    coordinator process) to perform type-checking. Specifying ``--num-workers 0``
    (default) disables parallel checking. Specifying ``--num-workers auto``
    selects the number based on the CPU resources available to mypy.

    Automatic selection uses at most 8 workers because each worker adds roughly
    10% memory overhead. This cap does not apply when an explicit value is specified.

    This setting will override the ``MYPY_NUM_WORKERS`` environment
    variable if it is set.

Notes:

* An import cycle is always processed as a whole by a worker process. Thus,
  avoiding large import cycles in your code will *significantly* improve
  type-checking speed.

* Specifying a number of workers that is larger than the number of *physical*
  CPU cores is not beneficial, since mypy is usually CPU bound. Best way to
  tune the number of workers on a given machine is to start from 3-4 workers
  and increase the number while you see a performance improvement.

* Parallel mode requires the native parser, which is enabled by default since
  mypy 2.4 (see :option:`--no-native-parser <mypy --no-native-parser>`).


Advanced options
****************

The following flags are useful mostly for people who are interested
in developing or debugging mypy internals.

.. option:: --pdb

    This flag will invoke the Python debugger when mypy encounters
    a fatal error.

.. option:: --show-traceback, --tb

    If set, this flag will display a full traceback when mypy
    encounters a fatal error.

.. option:: --raise-exceptions

    Raise exception on fatal error.

.. option:: --custom-typing-module MODULE

    This flag lets you use a custom module as a substitute for the
    :py:mod:`typing` module.

.. option:: --custom-typeshed-dir DIR

    This flag specifies the directory where mypy looks for standard library typeshed
    stubs, instead of the typeshed that ships with mypy.  This is
    primarily intended to make it easier to test typeshed changes before
    submitting them upstream, but also allows you to use a forked version of
    typeshed.

    Note that this doesn't affect third-party library stubs. To test third-party stubs,
    for example try ``MYPYPATH=stubs/six mypy ...``.

.. _warn-incomplete-stub:

.. option:: --warn-incomplete-stub

    This flag modifies both the :option:`--disallow-untyped-defs` and
    :option:`--disallow-incomplete-defs` flags so they also report errors
    if stubs in typeshed are missing type annotations or has incomplete
    annotations. If both flags are missing, :option:`--warn-incomplete-stub`
    also does nothing.

    This flag is mainly intended to be used by people who want contribute
    to typeshed and would like a convenient way to find gaps and omissions.

    If you want mypy to report an error when your codebase *uses* an untyped
    function, whether that function is defined in typeshed or not, use the
    :option:`--disallow-untyped-calls` flag. See :ref:`untyped-definitions-and-calls`
    for more details.

.. _shadow-file:

.. option:: --shadow-file SOURCE_FILE SHADOW_FILE

    When mypy is asked to type check ``SOURCE_FILE``, this flag makes mypy
    read from and type check the contents of ``SHADOW_FILE`` instead. However,
    diagnostics will continue to refer to ``SOURCE_FILE``.

    Specifying this argument multiple times (``--shadow-file X1 Y1 --shadow-file X2 Y2``)
    will allow mypy to perform multiple substitutions.

    This allows tooling to create temporary files with helpful modifications
    without having to change the source file in place. For example, suppose we
    have a pipeline that adds ``reveal_type`` for certain variables.
    This pipeline is run on ``original.py`` to produce ``temp.py``.
    Running ``mypy --shadow-file original.py temp.py original.py`` will then
    cause mypy to type check the contents of ``temp.py`` instead of  ``original.py``,
    but error messages will still reference ``original.py``.

.. option:: --no-native-parser

    This disables the fast Rust-based native parser that parses directly
    to mypy AST, and uses the legacy parser based on the stdlib :py:mod:`ast`
    module instead. The native parser is the default since mypy 2.4.

    The legacy parser can only parse syntax supported by the Python version
    used to run mypy. The legacy parser will be removed in a future mypy release.


Report generation
*****************

If these flags are set, mypy will generate a report in the specified
format into the specified directory.

.. option:: --any-exprs-report DIR

    Causes mypy to generate a text file report documenting how many
    expressions of type ``Any`` are present within your codebase.

.. option:: --cobertura-xml-report DIR

    Causes mypy to generate a Cobertura XML type checking coverage report.

    To generate this report, you must either manually install the `lxml`_
    library or specify mypy installation with the setuptools extra
    ``mypy[reports]``.

.. option:: --html-report / --xslt-html-report DIR

    Causes mypy to generate an HTML type checking coverage report.

    To generate this report, you must either manually install the `lxml`_
    library or specify mypy installation with the setuptools extra
    ``mypy[reports]``.

.. option:: --linecount-report DIR

    Causes mypy to generate a text file report documenting the functions
    and lines that are typed and untyped within your codebase.

.. option:: --linecoverage-report DIR

    Causes mypy to generate a JSON file that maps each source file's
    absolute filename to a list of line numbers that belong to typed
    functions in that file.

.. option:: --lineprecision-report DIR

    Causes mypy to generate a flat text file report with per-module
    statistics of how many lines are typechecked etc.

.. option:: --txt-report / --xslt-txt-report DIR

    Causes mypy to generate a text file type checking coverage report.

    To generate this report, you must either manually install the `lxml`_
    library or specify mypy installation with the setuptools extra
    ``mypy[reports]``.

.. option:: --xml-report DIR

    Causes mypy to generate an XML type checking coverage report.

    To generate this report, you must either manually install the `lxml`_
    library or specify mypy installation with the setuptools extra
    ``mypy[reports]``.


Enabling incomplete/experimental features
*****************************************

.. option:: --enable-incomplete-feature {PreciseTupleTypes,InlineTypedDict}

    Some features may require several mypy releases to implement, for example
    due to their complexity, potential for backwards incompatibility, or
    ambiguous semantics that would benefit from feedback from the community.
    You can enable such features for early preview using this flag. Note that
    it is not guaranteed that all features will be ultimately enabled by
    default. In *rare cases* we may decide to not go ahead with certain
    features.

List of currently incomplete/experimental features:

* ``PreciseTupleTypes``: this feature will infer more precise tuple types in
  various scenarios. Before variadic types were added to the Python type system
  by :pep:`646`, it was impossible to express a type like "a tuple with
  at least two integers". The best type available was ``tuple[int, ...]``.
  Therefore, mypy applied very lenient checking for variable-length tuples.
  Now this type can be expressed as ``tuple[int, int, *tuple[int, ...]]``.
  For such more precise types (when explicitly *defined* by a user) mypy,
  for example, warns about unsafe index access, and generally handles them
  in a type-safe manner. However, to avoid problems in existing code, mypy
  does not *infer* these precise types when it technically can. Here are
  notable examples where ``PreciseTupleTypes`` infers more precise types:

  .. code-block:: python

     numbers: tuple[int, ...]

     more_numbers = (1, *numbers, 1)
     reveal_type(more_numbers)
     # Without PreciseTupleTypes: tuple[int, ...]
     # With PreciseTupleTypes: tuple[int, *tuple[int, ...], int]

     other_numbers = (1, 1) + numbers
     reveal_type(other_numbers)
     # Without PreciseTupleTypes: tuple[int, ...]
     # With PreciseTupleTypes: tuple[int, int, *tuple[int, ...]]

     if len(numbers) > 2:
         reveal_type(numbers)
         # Without PreciseTupleTypes: tuple[int, ...]
         # With PreciseTupleTypes: tuple[int, int, int, *tuple[int, ...]]
     else:
         reveal_type(numbers)
         # Without PreciseTupleTypes: tuple[int, ...]
         # With PreciseTupleTypes: tuple[()] | tuple[int] | tuple[int, int]

* ``InlineTypedDict``: this feature enables non-standard syntax for inline
  :ref:`TypedDicts <typeddict>`, for example:

  .. code-block:: python

     def test_values() -> {"width": int, "description": str}:
         return {"width": 42, "description": "test"}



Miscellaneous
*************

.. option:: --install-types

    This flag causes mypy to install known missing stub packages for
    third-party libraries using pip.  It will display the pip command
    that will be run, and expects a confirmation before installing
    anything. For security reasons, these stubs are limited to only a
    small subset of manually selected packages that have been
    verified by the typeshed team. These packages include only stub
    files and no executable code.

    If you use this option without providing any files or modules to
    type check, mypy will install stub packages suggested during the
    previous mypy run. If there are files or modules to type check,
    mypy first type checks those, and proposes to install missing
    stubs at the end of the run, but only if any missing modules were
    detected.

    .. note::

        This is new in mypy 0.900. Previous mypy versions included a
        selection of third-party package stubs, instead of having
        them installed separately.

.. option:: --non-interactive

   When used together with :option:`--install-types <mypy
   --install-types>`, this causes mypy to install all suggested stub
   packages using pip without asking for confirmation, and then
   continues to perform type checking using the installed stubs, if
   some files or modules are provided to type check.

   This is implemented as up to two mypy runs internally. The first run
   is used to find missing stub packages, and output is shown from
   this run only if no missing stub packages were found. If missing
   stub packages were found, they are installed and then another run
   is performed.

.. option:: --junit-xml JUNIT_XML_OUTPUT_FILE

    Causes mypy to generate a JUnit XML test result document with
    type checking results. This can make it easier to integrate mypy
    with continuous integration (CI) tools.

.. option:: --junit-format {global,per_file}

    If --junit-xml is set, specifies format.
    global (default): single test with all errors;
    per_file: one test entry per file with failures.

.. option:: --find-occurrences CLASS.MEMBER

    This flag will make mypy print out all usages of a class member
    based on static type information. This feature is experimental.

.. option:: --scripts-are-modules

    This flag will give command line arguments that appear to be
    scripts (i.e. files whose name does not end in ``.py``)
    a module name derived from the script name rather than the fixed
    name :py:mod:`__main__`.

    This lets you check more than one script in a single mypy invocation.
    (The default :py:mod:`__main__` is technically more correct, but if you
    have many scripts that import a large package, the behavior enabled
    by this flag is often more convenient.)

.. _lxml: https://pypi.org/project/lxml/
.. _SQLite: https://www.sqlite.org/