pytype

A static type analyzer for Python code

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Error classes

pytype has the following classes of errors, which can be disabled with a pytype: disable=error-class directive. For example, to suppress an error for a missing attribute foo:

x = a.foo  # pytype: disable=attribute-error

or, to suppress all attribute errors for a block of code:

# pytype: disable=attribute-error
x = a.foo
y = a.bar
# pytype: enable=attribute-error

See Silencing Errors for a more detailed example.

annotation-type-mismatch

A variable had a type annotation and an assignment with incompatible types.

Example:

x : int = 'hello world'

NOTE: This is currently only checked for fields within a @dataclass definition.

attribute-error

The attribute being accessed may not exist. Often, the reason is that the attribute is declared in a method other than __new__ or __init__:

class A(object):
  def make_foo(self):
    self.foo = 42
  def consume_foo(self):
    return self.foo  # attribute-error

To make pytype aware of foo, declare it as a class attribute (with the literal ellipses) and supply the type in a type comment:

class A(object):
  foo = ...  # type: int

bad-concrete-type

A generic type was instantiated with incorrect concrete types. Example:

from typing import Generic, TypeVar

T = TypeVar('T', int, float)

class A(Generic[T]):
  pass

obj = A[str]()  # bad-concrete-type

bad-function-defaults

An attempt was made to set the __defaults__ attribute of a function with an object that is not a constant tuple. Example:

import collections
X = collections.namedtuple("X", "a")
X.__new__.__defaults__ = [None]  # bad-function-defaults

bad-return-type

At least one of the possible types for the return value does not match the declared return type. Example:

def f(x) -> int:
  if x:
    return 42
  else:
    return None  # bad-return-type

bad-slots

An attempt was made to set the __slots__ attribute of a class using an object that’s not a string.

class Foo(object):
  __slots__ = (1, 2, 3)

bad-unpacking

A tuple was unpacked into the wrong number of variables. Example:

a, b = (1, 2, 3)  # bad-unpacking

base-class-error

The class definition uses an illegal value for a base class. Example:

class A(42):  # base-class-error
  pass

duplicate-keyword-argument

A positional argument was supplied again as a keyword argument. Example:

def f(x):
  pass
f(True, x=False)  # duplicate-keyword-argument

If you believe you are seeing this error due to a bug on pytype’s end, see this section for where the type information we use is located.

ignored-abstractmethod

The abc.abstractmethod decorator was used in a non-abstract class. Example:

import abc
class A(object):  # ignored-abstractmethod
  @abc.abstractmethod
  def f(self):
    pass

Add the abc.ABCMeta metaclass to fix this issue:

import abc
class A(metaclass=abc.ABCMeta):
  @abc.abstractmethod
  def f(self):
    pass

ignored-metaclass

A Python 2-only metaclass declaration was found. Example:

class A(object):
  __metaclass__ = Meta

For Python 3-only code, the fix is:

class A(metaclass=Meta):
  ...

For Python 2-and-3 code, two equally good fixes are:

import six
@six.add_metaclass(Meta)
class A(object):
  ...

or:

import six
class A(six.with_metaclass(Meta, object)):
  ...

ignored-type-comment

A type comment was found on a line on which type comments are not allowed. Example:

def f():
  return 42  # type: float  # ignored-type-comment

import-error

The module being imported was not found.

invalid-annotation

Something is wrong with this annotation. Examples:

from typing import List, TypeVar, Union

T = TypeVar("T")
condition = ...  # type: bool
class _Foo: ...
def Foo():
  return _Foo()

def f(x: List[int, str]):  # bad: too many parameters for List
  pass
def f(x: T):  # bad: the TypeVar appears only once in the signature
  pass
def f(x: Foo):  # bad: not a type
  pass
def f(x: Union):  # bad: no options in the union
  pass
def f(x: int if condition else str):  # bad: ambiguous type
  pass

You will also see this error if you use a forward reference in typing.cast or pass a bad type to attr.ib:

import attr
import typing

v = typing.cast("A", None)  # invalid-annotation
class A(object):
  pass

@attr.s
class Foo(object):
  v = attr.ib(type=zip)  # invalid-annotation

The solutions are to use a type comment and to fix the type:

import attr

v = None  # type: "A"
class A(object):
  pass

@attr.s
class Foo(object):
  v = attr.ib(type=list)

invalid-directive

The error name is misspelled in a pytype disable/enable directive. Example with a misspelled name-error:

x = TypeDefinedAtRuntime  # pytype: disable=nmae-error  # invalid-directive

invalid-function-definition

An invalid function was constructed via metaprogramming (typically with a decorator such as @dataclass). Example:

from dataclasses import dataclass

@dataclass
class A:
  x : int = 10
  y : str

which creates

def __init__(x: int = 10, y: str):
  ...

with a non-default argument following a default one.

invalid-function-type-comment

Something was wrong with this function type comment. Examples:

def f(x):
  # type: (int)  # bad: missing return type
  pass
def f(x):
  # type: () -> None  # bad: too few arguments
  pass
def f(x):
  # type: int -> None  # bad: missing parentheses
  pass

invalid-namedtuple-arg

The typename or one of the field names in the namedtuple definition is invalid. Field names:

Also, there can be no duplicate field names. The typename has the same requirements, except that it can start with “_”.

invalid-super-call

A call to super without any arguments (Python 3) is being made from an invalid context. A super call without any arguments should be made from a method or a function defined within a class. Also, the caller should have at least one positional argument.

invalid-type-comment

Something was wrong with this type comment. Examples:

  x = None  # type: NonexistentType  # bad: undefined type
  y = None  # type: int if x else str  # bad: ambiguous type

invalid-typevar

Something was wrong with this TypeVar definition. Examples:

from typing import TypeVar
T = TypeVar("S")  # bad: storing TypeVar "S" as "T"
T = TypeVar(42)  # bad: using a non-str value for the TypeVar name
T = TypeVar("T", str)  # bad: supplying a single constraint (did you mean `bound=str`?)
T = TypeVar("T", 0, 100)  # bad: 0 and 100 are not types

key-error

The dictionary key doesn’t exist. Example:

x = {}
y = x["y"]  # key-error

late-directive

A # pytype: disable without a matching following enable or a # type: ignore appeared on its own line after the first top-level definition. Such a directive takes effect for the rest of the file, regardless of indentation, which is probably not what you want:

def f() -> bool:
  # pytype: disable=bad-return-type  # late-directive
  return 42

Two equally acceptable fixes:

def f() -> bool:
  return 42  # pytype: disable=bad-return-type
# pytype: disable=bad-return-type
def f() -> bool:
  return 42
# pytype: enable=bad-return-type

missing-parameter

The function was called with a parameter missing. Example:

def add(x, y):
  return x + y
add(42)  # missing-parameter

If you believe you are seeing this error due to a bug on pytype’s end, see this section for where the type information we use is located.

module-attr

The module attribute being accessed may not exist. Example:

import sys
sys.nonexistent_attribute  # module-attr

mro-error

A valid method resolution order cannot be created for the class being defined. Often, the culprit is cyclic inheritance:

class A(object):
  pass
class B(object, A):  # mro-error
  pass

name-error

This name does not exist in the current namespace. Note that types like List, Dict, etc., need to be imported from the typing module:

MyListType = List[str]  # name-error
from typing import List

MyListType = List[str]

not-callable

The object being called or instantiated is not callable. Example:

x = 42
y = x()  # not-callable

not-indexable

The object being indexed is not indexable. Example:

tuple[3]  # not-indexable

not-instantiable

The class cannot be instantiated because it has abstract methods. Example:

import abc
class A(metaclass=abc.ABCMeta):
  @abc.abstractmethod
  def f(self):
    pass
A()  # not-instantiable

not-supported-yet

This feature is not yet supported by pytype.

not-writable

The object an attribute was set on doesn’t have that attribute, or that attribute isn’t writable:

class Foo(object):
  __slots__ = ("x", "y")

Foo().z = 42  # not-writable

pyi-error

The pyi file contains a syntax error.

If you encounter this error in a pyi file that you did not create yourself, please file a bug.

python-compiler-error

The Python code contains a syntax error.

recursion-error

A recursive definition was found in a pyi file. Example:

class A(B): ...
class B(A): ...

If you encounter this error in a pyi file that you did not create yourself, please file a bug.

redundant-function-type-comment

Using both inline annotations and a type comment to annotate the same function is not allowed. Example:

def f() -> None:
  # type: () -> None  # redundant-function-type-comment
  pass

reveal-type

The error message displays the type of the expression passed to it. Example:

import os
reveal_type(os.path.join("hello", u"world"))  # reveal-type: unicode

This feature is implemented as an error to ensure that reveal_type() calls are removed after debugging.

unbound-type-param

This error currently applies only to pyi files. The type parameter is not bound to a class or function. Example:

from typing import AnyStr
x = ...  # type: AnyStr  # unbound-type-param

Unbound type parameters are meaningless as types. If you want to take advantage of types specified by a type parameter’s constraints or bound, specify those directly. So the above example should be rewritten as:

from typing import Union
x = ...  # type: Union[str,  unicode]

unsupported-operands

A binary operator was called with incompatible arguments. Example:

x = "hello" ^ "world"  # unsupported-operands

wrong-arg-count

The function was called with the wrong number of arguments. Example:

def add(x, y):
  return x + y
add(1, 2, 3)  # wrong-arg-count

If you believe you are seeing this error due to a bug on pytype’s end, see this section for where the type information we use is located.

wrong-arg-types

The function was called with the wrong argument types. Example:

def f(x: int):
  pass
f(42.0)  # wrong-arg-types

If you believe you are seeing this error due to a bug on pytype’s end, see this section for where the type information we use is located.

wrong-keyword-args

The function was called with the wrong keyword arguments. Example:

def f(x=True):
  pass
f(y=False)  # wrong-keyword-args

If you believe you are seeing this error due to a bug on pytype’s end, see this section for where the type information we use is located.