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, or .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.

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 *`s (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 qualified_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 the configuration sections is:
    1. Sections with concrete module names (foo.bar)
    2. Sections with “unstructured” wildcard patterns (foo.*.baz), with sections later in the configuration file overriding sections earlier.
    3. Sections with “well-structured” wildcard patterns (foo.bar.*), with more specific overriding more general.
    4. Command line options.
    5. 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.

Global flags

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

  • python_version (string) specifies the Python version used to parse and check the target program. The format is 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.
  • always_true (comma-separated list of strings) gives variable names that will be treated as compile-time constants that are always true.
  • always_false (comma-separated list of strings) gives variable names that will be treated as compile-time constants that are always false.
  • custom_typing_module (string) specifies the name of an alternative module which is to be considered equivalent to the typing module.
  • custom_typeshed_dir (string) specifies the name of an alternative directory which is used to look for stubs instead of the default typeshed directory.
  • 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.
  • warn_incomplete_stub (Boolean, default False) warns for missing type annotation in typeshed. This is only relevant in combination with check_untyped_defs.
  • warn_redundant_casts (Boolean, default False) warns about casting an expression to its inferred type.
  • warn_unused_configs (Boolean, default False) warns about per-module sections in the config file that didn’t match any files processed in the current run.
  • scripts_are_modules (Boolean, default False) makes script x become module x instead of __main__. This is useful when checking multiple scripts in a single run.
  • verbosity (integer, default 0) controls how much debug output will be generated. Higher numbers are more verbose.
  • pdb (Boolean, default False) invokes pdb on fatal error.
  • show_traceback (Boolean, default False) shows traceback on fatal error.
  • dump_type_stats (Boolean, default False) dumps stats about type definitions.
  • dump_inference_stats (Boolean, default False) dumps stats about type inference.
  • incremental (Boolean, default True) enables incremental mode.
  • cache_dir (string, default .mypy_cache) stores module cache info in the given folder in incremental mode. The cache is only read in incremental mode, but it is always written unless the value is set to /dev/null (UNIX) or nul (Windows).
  • quick_and_dirty (Boolean, default False) enables quick mode.
  • show_error_context (Boolean, default False) shows context notes before errors.
  • show_column_numbers (Boolean, default False) shows column numbers in error messages.

Per-module flags

The following flags may vary per module. They may also be specified in the global section; the global section provides defaults which are overridden by the pattern sections matching the module name.

Note

If multiple pattern sections match a module, the options from the most specific section are used where they disagree. This means that foo.bar will take values from sections with the patterns foo.bar, foo.bar.*, and foo.*, but when they specify different values, it will use values from foo.bar before foo.bar.* before foo.*.

  • 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 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. Note that if pattern matching is used, the pattern should match the name of the imported module, not the module containing the import statement.

  • follow_imports_for_stubs (Boolean, 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.

  • ignore_missing_imports (Boolean, default False) suppress error messages about imports that cannot be resolved. Note that if pattern matching is used, the pattern should match the name of the imported module, not the module containing the import statement.

  • silent_imports (Boolean, deprecated) equivalent to follow_imports=skip plus ignore_missing_imports=True.

  • almost_silent (Boolean, deprecated) equivalent to follow_imports=skip.

  • strict_optional (Boolean, 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.

  • disallow_any_unimported (Boolean, default false) disallows usage of types that come from unfollowed imports (such types become aliases for Any).

  • disallow_any_expr (Boolean, default false) disallows all expressions in the module that have type Any.

  • disallow_any_decorated (Boolean, default false) disallows functions that have Any in their signature after decorator transformation.

  • disallow_any_explicit (Boolean, default false) disallows explicit Any in type positions such as type annotations and generic type parameters.

  • disallow_any_generics (Boolean, default false) disallows usage of generic types that do not specify explicit type parameters.

  • disallow_incomplete_defs (Boolean, default false) disallow defining functions with incomplete type annotations. See –disallow-incomplete-defs option.

  • disallow_subclassing_any (Boolean, default False) disallows subclassing a value of type Any. See –disallow-subclassing-any option.

  • disallow_untyped_calls (Boolean, default False) disallows calling functions without type annotations from functions with type annotations.

  • disallow_untyped_defs (Boolean, default False) disallows defining functions without type annotations or with incomplete type annotations.

  • check_untyped_defs (Boolean, default False) type-checks the interior of functions without type annotations.

  • debug_cache (Boolean, default False) writes the incremental cache JSON files using a more readable, but slower format.

  • show_none_errors (Boolean, default True) shows errors related to strict None checking, if the global strict_optional flag is enabled.

  • ignore_errors (Boolean, default False) ignores all non-fatal errors.

  • warn_no_return (Boolean, default True) shows errors for missing return statements on some execution paths.

  • warn_return_any (Boolean, default False) shows a warning when returning a value with type Any from a function declared with a non- Any return type.

  • warn_unused_ignores (Boolean, default False) warns about unneeded # type: ignore comments.

  • strict_boolean (Boolean, default False) makes using non-boolean expressions in conditions an error.

  • no_implicit_optional (Boolean, default false) changes the treatment of arguments with a default value of None by not implicitly making their type Optional

Examples

You might put this in your mypy.ini file at the root of your repo:

[mypy]
python_version = 2.7
[mypy-foo.*]
disallow_untyped_defs = True

This automatically sets --python-version 2.7 (a.k.a. --py2) for all mypy runs in this tree, and also selectively turns on the --disallow-untyped-defs flag for all modules in the foo package. This issues an error for function definitions without type annotations in that subdirectory only.

If you would like to ignore specific imports, instead of ignoring all missing imports with --ignore-missing-imports, use a section of the configuration file per module such as the following to ignore missing imports from lib_module:

[mypy-lib_module]
ignore_missing_imports = True

Note

Configuration flags are liable to change between releases.