The mypy configuration file

Mypy supports reading configuration settings from a file. By default it uses the file mypy.ini with fallback to setup.cfg in the current directory, then $XDG_CONFIG_HOME/mypy/config, then ~/.config/mypy/config, and finally .mypy.ini in the user home directory if none of them are found; the --config-file command-line flag can be used to read a different file instead (see –config-file).

It is important to understand that there is no merging of configuration files, as it would lead to ambiguity. The --config-file flag has the highest precedence and must be correct; otherwise mypy will report an error and exit. Without command line option, mypy will look for defaults, but will use only one of them. The first one to read is mypy.ini, and then setup.cfg.

Most flags correspond closely to command-line flags but there are some differences in flag names and some flags may take a different value based on the module being processed.

Config file format

The configuration file format is the usual ini file format. It should contain section names in square brackets and flag settings of the form NAME = VALUE. Comments start with # characters.

  • A section named [mypy] must be present. This specifies the global flags. The setup.cfg file is an exception to this.

  • Additional sections named [mypy-PATTERN1,PATTERN2,...] may be present, where PATTERN1, PATTERN2, etc., are comma-separated patterns of fully-qualified module names, with some components optionally replaced by the ‘*’ character (e.g. foo.bar, foo.bar.*, foo.*.baz). These sections specify additional flags that only apply to modules whose name matches at least one of the patterns.

    A pattern of the form qualified_module_name matches only the named module, while dotted_module_name.* matches dotted_module_name and any submodules (so foo.bar.* would match all of foo.bar, foo.bar.baz, and foo.bar.baz.quux).

    Patterns may also be “unstructured” wildcards, in which stars may appear in the middle of a name (e.g site.*.migrations.*). Stars match zero or more module components (so site.*.migrations.* can match site.migrations).

    When options conflict, the precedence order for configuration is:
    1. Inline configuration in the source file
    2. Sections with concrete module names (foo.bar)
    3. Sections with “unstructured” wildcard patterns (foo.*.baz), with sections later in the configuration file overriding sections earlier.
    4. Sections with “well-structured” wildcard patterns (foo.bar.*), with more specific overriding more general.
    5. Command line options.
    6. Top-level configuration file options.

The difference in precedence order between “structured” patterns (by specificity) and “unstructured” patterns (by order in the file) is unfortunate, and is subject to change in future versions.

Note

The warn_unused_configs flag may be useful to debug misspelled section names.

Note

Configuration flags are liable to change between releases.

Examples

Here is an example of a mypy.ini file. To use this config file, place it at the root of your repo and run mypy.

# Global options:

[mypy]
python_version = 2.7
warn_return_any = True
warn_unused_configs = True

# Per-module options:

[mypy-mycode.foo.*]
disallow_untyped_defs = True

[mypy-mycode.bar]
warn_return_any = False

[mypy-somelibrary]
ignore_missing_imports = True

This config file specifies three global options in the [mypy] section. These three options will:

  1. Type-check your entire project assuming it will be run using Python 2.7. (This is equivalent to using the --python-version 2.7 or --2 flag).
  2. Report an error whenever a function returns a value that is inferred to have type Any.
  3. Report any config options that are unused by mypy. (This will help us catch typos when making changes to our config file).

Next, this module specifies three per-module options. The first two options change how mypy type checks code in mycode.foo.* and mycode.bar, which we assume here are two modules that you wrote. The final config option changes how mypy type checks somelibrary, which we assume here is some 3rd party library you’ve installed and are importing. These options will:

  1. Selectively disallow untyped function definitions only within the mycode.foo package – that is, only for function definitions defined in the mycode/foo directory.
  2. Selectively disable the “function is returning any” warnings within mycode.bar only. This overrides the global default we set earlier.
  3. Suppress any error messages generated when your codebase tries importing the module somelibrary. This is useful if somelibrary is some 3rd party library missing type hints.

Per-module and global options

The following config options may be set either globally (in the [mypy] section) or on a per-module basis (in sections like [mypy-foo.bar]).

If you set an option both globally and for a specific module, the module configuration options take precedence. This lets you set global defaults and override them on a module-by-module basis. If multiple pattern sections match a module, the options from the most specific section are used where they disagree.

Options that take a boolean value may be inverted by adding no_ to their name or by (when applicable) swapping their prefix from disallow to allow (and vice versa).

Import discovery

For more information, see the import discovery section of the command line docs.

Note: this section describes options that can be used both globally and per-module. See below for a list of import discovery options that may be used only globally.

ignore_missing_imports (bool, default False)

Suppresses error messages about imports that cannot be resolved.

If this option is used in a per-module section, the module name should match the name of the imported module, not the module containing the import statement.

follow_imports (string, default normal)

Directs what to do with imports when the imported module is found as a .py file and not part of the files, modules and packages provided on the command line.

The four possible values are normal, silent, skip and error. For explanations see the discussion for the –follow-imports command line flag.

If this option is used in a per-module section, the module name should match the name of the imported module, not the module containing the import statement.

follow_imports_for_stubs (bool, default False)

Determines whether to respect the follow_imports setting even for stub (.pyi) files.

Used in conjunction with follow_imports=skip, this can be used to suppress the import of a module from typeshed, replacing it with Any.

Used in conjunction with follow_imports=error, this can be used to make any use of a particular typeshed module an error.

Disallow dynamic typing

For more information, see the disallowing dynamic typing section of the command line docs.

disallow_any_unimported (bool, default False)
Disallows usage of types that come from unfollowed imports (anything imported from an unfollowed import is automatically given a type of Any).
disallow_any_expr (bool, default False)
Disallows all expressions in the module that have type Any.
disallow_any_decorated (bool, default False)
Disallows functions that have Any in their signature after decorator transformation.
disallow_any_explicit (bool, default False)
Disallows explicit Any in type positions such as type annotations and generic type parameters.
disallow_any_generics (bool, default False)
Disallows usage of generic types that do not specify explicit type parameters.
disallow_subclassing_any (bool, default False)
Disallows subclassing a value of type Any.

Untyped definitions and calls

For more information, see the untyped definitions and calls section of the command line docs.

disallow_untyped_calls (bool, default False)
Disallows calling functions without type annotations from functions with type annotations.
disallow_untyped_defs (bool, default False)
Disallows defining functions without type annotations or with incomplete type annotations.
disallow_incomplete_defs (bool, default False)
Disallows defining functions with incomplete type annotations.
check_untyped_defs (bool, default False)
Type-checks the interior of functions without type annotations.
disallow_untyped_decorators (bool, default False)
Reports an error whenever a function with type annotations is decorated with a decorator without annotations.

None and optional handling

For more information, see the None and optional handling section of the command line docs.

no_implicit_optional (bool, default False)
Changes the treatment of arguments with a default value of None by not implicitly making their type Optional.
strict_optional (bool, default True)

Enables or disables strict Optional checks. If False, mypy treats None as compatible with every type.

Note: This was False by default in mypy versions earlier than 0.600.

Configuring warnings

For more information, see the configuring warnings section of the command line docs.

warn_unused_ignores (bool, default False)
Warns about unneeded # type: ignore comments.
warn_no_return (bool, default True)
Shows errors for missing return statements on some execution paths.
warn_return_any (bool, default False)
Shows a warning when returning a value with type Any from a function declared with a non- Any return type.
warn_unreachable (bool, default False)
Shows a warning when encountering any code inferred to be unreachable or redundant after performing type analysis.

Suppressing errors

Note: these configuration options are available in the config file only. There is no analog available via the command line options.

show_none_errors (bool, default True)
Shows errors related to strict None checking, if the global strict_optional flag is enabled.
ignore_errors (bool, default False)
Ignores all non-fatal errors.

Miscellaneous strictness flags

allow_redefinition (bool, default False)
Allows variables to be redefined with an arbitrary type, as long as the redefinition is in the same block and nesting level as the original definition.
implicit_reexport (bool, default True)

By default, imported values to a module are treated as exported and mypy allows other modules to import them. When false, mypy will not re-export unless the item is imported using from-as. Note that mypy treats stub files as if this is always disabled. For example:

# This won't re-export the value
from foo import bar
# This will re-export it as bar and allow other modules to import it
from foo import bar as bar
strict_equality (bool, default False)
Prohibit equality checks, identity checks, and container checks between non-overlapping types.

Platform configuration

always_true (comma-separated list of strings)
Specifies a list of variables that mypy will treat as compile-time constants that are always true.
always_false (comma-separated list of strings)
Specifies a list of variables that mypy will treat as compile-time constants that are always false.

Global-only options

The following options may only be set in the global section ([mypy]).

Import discovery

For more information, see the import discovery section of the command line docs.

Note: this section describes only global-only import discovery options. See above for a list of import discovery options that may be used both per-module and globally.

namespace_packages (bool, default False)
Enables PEP 420 style namespace packages. See the corresponding flag for more information.
python_executable (string)
Specifies the path to the Python executable to inspect to collect a list of available PEP 561 packages. Defaults to the executable used to run mypy.
no_silence_site_packages (bool, default False)
Enables reporting error messages generated within PEP 561 compliant packages. Those error messages are suppressed by default, since you are usually not able to control errors in 3rd party code.
mypy_path (string)
Specifies the paths to use, after trying the paths from MYPYPATH environment variable. Useful if you’d like to keep stubs in your repo, along with the config file.
files (string)
A comma-separated list of paths which should be checked by mypy if none are given on the command line. Supports recursive file globbing using [the glob library](https://docs.python.org/3/library/glob.html), where * (e.g. *.py) matches files in the current directory and **/ (e.g. **/*.py) matches files in any directories below the current one.

Platform configuration

For more information, see the platform configuration section of the command line docs.

python_version (string)
Specifies the Python version used to parse and check the target program. The string should be in the format DIGIT.DIGIT – for example 2.7. The default is the version of the Python interpreter used to run mypy.
platform (string)
Specifies the OS platform for the target program, for example darwin or win32 (meaning OS X or Windows, respectively). The default is the current platform as revealed by Python’s sys.platform variable.

Incremental mode

For more information, see the incremental mode section of the command line docs.

incremental (bool, default True)
Enables incremental mode.
cache_dir (string, default .mypy_cache)
Specifies the location where mypy stores incremental cache info. Note that the cache is only read when incremental mode is enabled but is always written to, unless the value is set to /dev/nul (UNIX) or nul (Windows).
skip_version_check (bool, default False)
Makes mypy use incremental cache data even if it was generated by a different version of mypy. (By default, mypy will perform a version check and regenerate the cache if it was written by older versions of mypy.)

Configuring error messages

For more information, see the configuring error messages section of the command line docs.

show_error_context (bool, default False)
Prefixes each error with the relevant context.
show_column_numbers (bool, default False)
Shows column numbers in error messages.

Advanced options

For more information, see the advanced flags section of the command line docs.

pdb (bool, default False)
Invokes pdb on fatal error.
show_traceback (bool, default False)
Shows traceback on fatal error.
custom_typing_module (string)
Specifies a custom module to use as a substitute for the typing module.
custom_typeshed_dir (string)
Specifies an alternative directory to look for stubs instead of the default typeshed directory.
warn_incomplete_stub (bool, default False)
Warns about missing type annotations in typeshed. This is only relevant in combination with disallow_untyped_defs or disallow_incomplete_defs.

Miscellaneous

warn_redundant_casts (bool, default False)
Warns about casting an expression to its inferred type.
scripts_are_modules (bool, default False)
Makes script x become module x instead of __main__. This is useful when checking multiple scripts in a single run.
warn_unused_configs (bool, default False)
Warns about per-module sections in the config file that do not match any files processed when invoking mypy. (This requires turning off incremental mode using incremental = False.)
verbosity (integer, default 0)
Controls how much debug output will be generated. Higher numbers are more verbose.
new_semantic_analyzer (bool, default True)
Enables the new, improved, semantic analyzer. (See The mypy command line for more information.)