Provided by: mypy_0.942-1ubuntu1_all 
NAME
mypy - Optional static typing for Python
SYNOPSIS
mypy [-h] [-v] [-V] [-m MODULE] [-p PACKAGE] [-c PROGRAM_TEXT] [OPTIONS...] [FILES ...]
DESCRIPTION
Mypy is a static type checker for Python 3 and Python 2.7. If you sprinkle your code with type
annotations, mypy can type check your code and find common bugs. As mypy is a static analyzer, or a
lint-like tool, the type annotations are just hints for mypy and don’t interfere when running your
program. You run your program with a standard Python interpreter, and the annotations are treated
effectively as comments.
Using the Python 3 function annotation syntax (using the PEP 484 notation) or a comment-based annotation
syntax for Python 2 code, you will be able to efficiently annotate your code and use mypy to check the
code for common errors. Mypy has a powerful and easy-to-use type system with modern features such as type
inference, generics, callable types, tuple types, union types, and structural subtyping.
Mypy is invoked with the paths the user needs to check:
$ mypy foo.py bar.py some_directory
The directories are checked recursively to find Python source files.
OPTIONS
This section documents mypy's command line interface. You can view a quick summary of the available flags
by running 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 running-mypy.
-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.
-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
--module apart from this behavior.
-c PROGRAM_TEXT, --command PROGRAM_TEXT
Asks mypy to type check the provided string as a program.
--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$'
but_still_check/setup.py.
In particular, --exclude does not affect mypy's import following. You can use a per-module
:confval:`follow_imports`
config option to additionally avoid mypy from following imports and checking code you do not wish
to be checked.
Note that mypy will never recursively discover files and directories named "site-packages",
"node_modules" or "__pycache__", or those whose name starts with a period, exactly as --exclude
'/(site-packages|node_modules|__pycache__|\..*)/$' would. Mypy will also never recursively
discover files with extensions other than .py or .pyi.
Optional arguments
-h, --help
Show help message and exit.
-v, --verbose
More verbose messages.
-V, --version
Show program's version number and exit.
Config file
--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 --config-file= (with no filename) will ignore all config files.
See config-file for the syntax of configuration files.
--warn-unused-configs
This flag makes mypy warn about unused [mypy-<pattern>] config file sections. (This requires
turning off incremental mode using --no-incremental.)
Import discovery
The following flags customize how exactly mypy discovers and follows imports.
--namespace-packages
This flag enables import discovery to use namespace packages (see PEP 420). In particular, this
allows discovery of imported packages that don't have an __init__.py (or __init__.pyi) file.
Namespace packages are found (using the PEP 420 rules, which prefers "classic" packages over
namespace packages) along the module search path -- this is primarily set from the source files
passed on the command line, the MYPYPATH environment variable, and the
:confval:`mypy_path`
config option.
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 Mapping file paths to modules for details.
--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 conjunction with --namespace-packages. See Mapping
file paths to modules for details.
--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 --ignore-missing-imports:
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 ignore-missing-imports.
--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 Following imports.
--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 installed-packages for more on making PEP 561 compliant packages.
--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 --python-executable.
--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.
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 version_and_platform_checks.
--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. Note that the
-2 and --py2 flags are aliases for --python-version 2.7.
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 --no-site-packages flag (see
import-discovery for more details).
-2, --py2
Equivalent to running --python-version 2.7.
NOTE:
To check Python 2 code with mypy, you'll need to install mypy with pip install 'mypy[python2]'.
--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 sys.platform.
--always-true NAME
This flag will treat all variables named NAME as compile-time constants that are always true.
This flag may be repeated.
--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
The Any type is used to represent a value that has a dynamic type. 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:
--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
--follow-imports=skip is set.
--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 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.
--disallow-any-decorated
This flag disallows functions that have Any in their signature after decorator transformation.
--disallow-any-explicit
This flag disallows explicit Any in type positions such as type annotations and generic type
parameters.
--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].
--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 --ignore-missing-imports)
or is ignored due to --follow-imports=skip 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
The following flags configure how mypy handles untyped function definitions or calls.
--disallow-untyped-calls
This flag reports an error whenever a function with type annotations calls a function defined
without annotations.
--disallow-untyped-defs
This flag reports an error whenever it encounters a function definition without type annotations.
--disallow-incomplete-defs
This flag reports an error whenever it encounters a partly annotated function definition.
--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.
--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
The following flags adjust how mypy handles values of type None. For more details, see
no_strict_optional.
--no-implicit-optional
This flag causes mypy to stop treating arguments with a None default value as having an implicit
Optional type.
For example, by default mypy will assume that the x parameter is of type Optional[int] in the code
snippet below since the default parameter is None:
def foo(x: int = None) -> None:
print(x)
If this flag is set, the above snippet will no longer type check: we must now explicitly indicate
that the type is Optional[int]:
def foo(x: Optional[int] = None) -> None:
print(x)
--no-strict-optional
This flag disables strict checking of Optional types and None values. With this option, mypy
doesn't generally check the use of None values -- they are valid everywhere. See
no_strict_optional for more about this feature.
Note: Strict optional checking was enabled by default starting in mypy 0.600, and in previous
versions it had to be explicitly enabled using --strict-optional (which is still accepted).
Configuring warnings
The following flags enable warnings for code that is sound but is potentially problematic or redundant in
some way.
--warn-redundant-casts
This flag will make mypy report an error whenever your code uses an unnecessary cast that can
safely be removed.
--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 --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.
--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 or a body that is just ellipsis (...). Empty functions are often
used for abstract methods.
Passing in --no-warn-no-return will disable these error messages in all cases.
--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.
--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.
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 two cases:
1. When the unreachable statement is a raise statement, is an assert False statement, or calls a
function that has the 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 was intentionally marked as unreachable using
version_and_platform_checks.
NOTE:
Mypy currently cannot detect and report unreachable or redundant code inside any functions
using type-variable-value-restriction.
This limitation will be removed in future releases of mypy.
Miscellaneous strictness flags
This section documents any other flags that do not neatly fall under any of the above sections.
--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.
--allow-redefinition
By default, mypy won't allow a variable to be redefined with an unrelated type. 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. Example where this can be
useful:
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:
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
--local-partial-types
In mypy, the most common cases for partial types are variables initialized using None, but without
explicit Optional annotations. By default, mypy won't check partial types spanning module top
level or class top level. This flag changes the behavior to only allow partial types at local
level, therefore it disallows inferring variable type for None from two assignments in different
scopes. For example:
from typing import Optional
a = None # Need type annotation here if using --local-partial-types
b = None # type: Optional[int]
class Foo:
bar = None # Need type annotation here if using --local-partial-types
baz = None # type: Optional[int]
def __init__(self) -> None:
self.bar = 1
reveal_type(Foo().bar) # Union[int, None] without --local-partial-types
Note: this option is always implicitly enabled in mypy daemon and will become enabled by default
for mypy in a future release.
--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:
# 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']
--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:
from typing import Text
items: list[int]
if 'some string' in items: # Error: non-overlapping container check!
...
text: Text
if text != b'other bytes': # Error: non-overlapping equality check!
...
assert text is not None # OK, check against None is allowed as a special case.
--strict
This flag mode enables all optional error checking flags. You can see the list of flags enabled
by strict mode in the full mypy --help output.
Note: the exact list of flags enabled by running --strict may change over time.
--disable-error-code
This flag allows disabling one or multiple error codes globally.
# no flag
x = 'a string'
x.trim() # error: "str" has no attribute "trim" [attr-defined]
# --disable-error-code attr-defined
x = 'a string'
x.trim()
--enable-error-code
This flag allows enabling one or multiple error codes globally.
Note: This flag will override disabled error codes from the --disable-error-code flag
# --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
The following flags let you adjust how much detail mypy displays in error messages.
--show-error-context
This flag will precede all errors with "note" messages explaining the context of the error. For
example, consider the following program:
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")
--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")
--show-error-codes
This flag will add an error code [<code>] to error messages. The error code is shown after each
error message:
prog.py:1: error: "str" has no attribute "trim" [attr-defined]
See error-codes for more information.
--pretty
Use visually nicer output in error messages: use soft word wrap, show source code snippets, and
show error location markers.
--no-color-output
This flag will disable color output in error messages, enabled by default.
--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.
--show-absolute-path
Show absolute paths to files.
--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 200.
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 daemon mode.
--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
--cache-dir flag below for more details.
--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 remote caching.
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).
--sqlite-cache
Use an SQLite database to store the cache.
--cache-fine-grained
Include fine-grained dependency information in the cache for the mypy daemon.
--skip-version-check
By default, mypy will ignore cache data generated by a different version of mypy. This flag
disables that behavior.
--skip-cache-mtime-checks
Skip cache internal consistency checks based on mtime.
Advanced options
The following flags are useful mostly for people who are interested in developing or debugging mypy
internals.
--pdb This flag will invoke the Python debugger when mypy encounters a fatal error.
--show-traceback, --tb
If set, this flag will display a full traceback when mypy encounters a fatal error.
--raise-exceptions
Raise exception on fatal error.
--custom-typing-module MODULE
This flag lets you use a custom module as a substitute for the typing module.
--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.
--warn-incomplete-stub
This flag modifies both the --disallow-untyped-defs and --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, --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 --disallow-untyped-calls flag. See
untyped-definitions-and-calls for more details.
--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.
Report generation
If these flags are set, mypy will generate a report in the specified format into the specified directory.
--any-exprs-report DIR
Causes mypy to generate a text file report documenting how many expressions of type Any are
present within your codebase.
--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].
--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].
--linecount-report DIR
Causes mypy to generate a text file report documenting the functions and lines that are typed and
untyped within your codebase.
--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.
--lineprecision-report DIR
Causes mypy to generate a flat text file report with per-module statistics of how many lines are
typechecked etc.
--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].
--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].
Miscellaneous
--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.
--non-interactive
When used together with --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.
--junit-xml JUNIT_XML
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.
--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.
--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 __main__.
This lets you check more than one script in a single mypy invocation. (The default __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.)
ENVIRONMENT
MYPYPATH
Additional module search path entries. The format is the same as the shell's $PATH: one or more
directory pathnames separated by colons.
SEE ALSO
dmypy(1)
Full documentation is available online at: http://mypy.readthedocs.io/en/latest/getting_started.html or
locally at: /usr/share/doc/mypy/html (requires mypy-doc package).
AUTHOR
Jukka Lehtosalo and contributors
Sep 07, 2022 MYPY(1)