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; 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 fnmatch patterns separated by commas. These sections specify additional flags that only apply to modules whose name matches at least one of the patterns.

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.
  • 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_ignores (Boolean, default False) warns about unneeded # type: ignore comments.
  • strict_optional (Boolean, default False) enables experimental strict Optional checks.
  • 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 False) 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 they are processed in unspecified order.

  • 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.
  • 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.
  • disallow_any (Comma-separated list, default empty) is an option to disallow various types of Any in a module. The flag takes a comma-separated list of the following arguments: unimported, unannotated, expr, decorated, explicit, generics. For explanations see the discussion for the –disallow-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.
  • 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

Example

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.

Note

Configuration flags are liable to change between releases.