Provided by: mypy_1.0.0-1_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.
--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 in the absence of __init__.py. 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.
--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 --fast-module-lookup 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 Mapping file paths to modules for details.
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.
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).
--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.
--implicit-optional
This flag causes mypy to treat arguments with a None default value as having an
implicit Optional type.
For example, if this flag is set, mypy would assume that the x parameter is
actually of type Optional[int] in the code snippet below since the default
parameter is None:
def foo(x: int = None) -> None:
print(x)
Note: This was disabled by default starting in mypy 0.980.
--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 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 --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: Optional[int] = None
class Foo:
bar = None # Need type annotation here if using --local-partial-types
baz: Optional[int] = None
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. See error-codes
for more information.
# 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()
--enable-error-code
This flag allows enabling one or multiple error codes globally. See error-codes
for more information.
Note: This flag will override disabled error codes from the --disable-error-code
flag.
# 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
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-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.
--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 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. To test third-party stubs,
for example try MYPYPATH=stubs/six mypy ....
--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
Feb 13, 2023 MYPY(1)