crates/ty_python_semantic/resources/mdtest/annotations/union.md
typing.Union can be used to construct union types in the same way as the | operator.
from typing import Union
a: Union[int, str]
a1: Union[int, bool]
a2: Union[int, Union[bytes, str]]
a3: Union[int, None]
a4: Union[Union[bytes, str]]
a5: Union[int]
a6: Union[()]
def f():
# revealed: int | str
reveal_type(a)
# Since bool is a subtype of int we simplify to int here. But we do allow assigning boolean values (see below).
# revealed: int
reveal_type(a1)
# revealed: int | bytes | str
reveal_type(a2)
# revealed: int | None
reveal_type(a3)
# revealed: bytes | str
reveal_type(a4)
# revealed: int
reveal_type(a5)
# revealed: Never
reveal_type(a6)
from typing import Union
a: Union[int, str]
a = 1
a = ""
a1: Union[int, bool]
a1 = 1
a1 = True
# error: [invalid-assignment] "Object of type `Literal[b""]` is not assignable to `int | str`"
a = b""
from typing_extensions import Union
a: Union[int, str]
def f():
# revealed: int | str
reveal_type(a)
from typing import Union
# error: [invalid-type-form] "`typing.Union` requires at least one argument when used in a parameter annotation"
def f(x: Union) -> None:
reveal_type(x) # revealed: Unknown
[environment]
python-version = "3.10"
X = int | str
def f(y: X):
reveal_type(y) # revealed: int | str
PEP-604 unions generally don't work on Python 3.9 and earlier:
[environment]
python-version = "3.9"
foo.py:
x: int | str # snapshot: unsupported-operator
class Foo:
def __init__(self):
self.x: int | str = 42 # snapshot: unsupported-operator
d = {}
d[0]: int | str = 42 # snapshot: unsupported-operator
error[unsupported-operator]: Unsupported `|` operation
--> src/foo.py:1:4
|
1 | x: int | str # snapshot: unsupported-operator
| ---^^^---
| | |
| | Has type `<class 'str'>`
| Has type `<class 'int'>`
|
info: PEP 604 `|` unions are only available on Python 3.10+ unless they are quoted
info: Python 3.9 was assumed when resolving types because it was specified on the command line
error[unsupported-operator]: Unsupported `|` operation
--> src/foo.py:5:17
|
5 | self.x: int | str = 42 # snapshot: unsupported-operator
| ---^^^---
| | |
| | Has type `<class 'str'>`
| Has type `<class 'int'>`
|
info: PEP 604 `|` unions are only available on Python 3.10+ unless they are quoted
info: Python 3.9 was assumed when resolving types because it was specified on the command line
error[unsupported-operator]: Unsupported `|` operation
--> src/foo.py:8:7
|
8 | d[0]: int | str = 42 # snapshot: unsupported-operator
| ---^^^---
| | |
| | Has type `<class 'str'>`
| Has type `<class 'int'>`
|
info: PEP 604 `|` unions are only available on Python 3.10+ unless they are quoted
info: Python 3.9 was assumed when resolving types because it was specified on the command line
But these runtime errors can be avoided if you add from __future__ import annotations to the top
of your file:
bar.py:
from __future__ import annotations
x: int | str
class Foo:
def __init__(self):
self.x: int | str = 42
d = {}
d[0]: int | str = 42
The following ones are still errors because from __future__ import annotations only stringifies
type annotations, not arbitrary runtime expressions:
baz.py:
X = str | int # snapshot: unsupported-operator
Y = tuple[str | int, ...] # snapshot: unsupported-operator
error[unsupported-operator]: Unsupported `|` operation
--> src/baz.py:1:5
|
1 | X = str | int # snapshot: unsupported-operator
| ---^^^---
| | |
| | Has type `<class 'int'>`
| Has type `<class 'str'>`
|
info: PEP 604 `|` unions are only available on Python 3.10+ unless they are quoted
info: Python 3.9 was assumed when resolving types because it was specified on the command line
error[unsupported-operator]: Unsupported `|` operation
--> src/baz.py:2:11
|
2 | Y = tuple[str | int, ...] # snapshot: unsupported-operator
| ---^^^---
| | |
| | Has type `<class 'int'>`
| Has type `<class 'str'>`
|
info: PEP 604 `|` unions are only available on Python 3.10+ unless they are quoted
info: Python 3.9 was assumed when resolving types because it was specified on the command line