4.4 KiB
sys.version_info
[environment]
python-version = "3.9"
The type of sys.version_info
The type of sys.version_info is sys._version_info, at least according to typeshed's stubs (which
we treat as the single source of truth for the standard library). This is quite a complicated type
in typeshed, so there are many things we don't fully understand about the type yet; this is the
source of several TODOs in this test file. Many of these TODOs should be naturally fixed as we
implement more type-system features in the future.
import sys
reveal_type(sys.version_info) # revealed: _version_info
Literal types from comparisons
Comparing sys.version_info with a 2-element tuple of literal integers always produces a Literal
type:
import sys
reveal_type(sys.version_info >= (3, 9)) # revealed: Literal[True]
reveal_type((3, 9) <= sys.version_info) # revealed: Literal[True]
reveal_type(sys.version_info > (3, 9)) # revealed: Literal[True]
reveal_type((3, 9) < sys.version_info) # revealed: Literal[True]
reveal_type(sys.version_info < (3, 9)) # revealed: Literal[False]
reveal_type((3, 9) > sys.version_info) # revealed: Literal[False]
reveal_type(sys.version_info <= (3, 9)) # revealed: Literal[False]
reveal_type((3, 9) >= sys.version_info) # revealed: Literal[False]
reveal_type(sys.version_info == (3, 9)) # revealed: Literal[False]
reveal_type((3, 9) == sys.version_info) # revealed: Literal[False]
reveal_type(sys.version_info != (3, 9)) # revealed: Literal[True]
reveal_type((3, 9) != sys.version_info) # revealed: Literal[True]
Non-literal types from comparisons
Comparing sys.version_info with tuples of other lengths will sometimes produce Literal types,
sometimes not:
import sys
reveal_type(sys.version_info >= (3, 9, 1)) # revealed: bool
reveal_type(sys.version_info >= (3, 9, 1, "final", 0)) # revealed: bool
# TODO: While this won't fail at runtime, the user has probably made a mistake
# if they're comparing a tuple of length >5 with `sys.version_info`
# (`sys.version_info` is a tuple of length 5). It might be worth
# emitting a lint diagnostic of some kind warning them about the probable error?
reveal_type(sys.version_info >= (3, 9, 1, "final", 0, 5)) # revealed: bool
reveal_type(sys.version_info == (3, 8, 1, "finallllll", 0)) # revealed: Literal[False]
Imports and aliases
Comparisons with sys.version_info still produce literal types, even if the symbol is aliased to
another name:
from sys import version_info
from sys import version_info as foo
reveal_type(version_info >= (3, 9)) # revealed: Literal[True]
reveal_type(foo >= (3, 9)) # revealed: Literal[True]
bar = version_info
reveal_type(bar >= (3, 9)) # revealed: Literal[True]
Non-stdlib modules named sys
Only comparisons with the symbol version_info from the sys module produce literal types:
package/__init__.py:
package/sys.py:
version_info: tuple[int, int] = (4, 2)
package/script.py:
from .sys import version_info
reveal_type(version_info >= (3, 9)) # revealed: bool
Accessing fields by name
The fields of sys.version_info can be accessed by name:
import sys
reveal_type(sys.version_info.major >= 3) # revealed: Literal[True]
reveal_type(sys.version_info.minor >= 9) # revealed: Literal[True]
reveal_type(sys.version_info.minor >= 10) # revealed: Literal[False]
But the micro, releaselevel and serial fields are inferred as @Todo until we support
properties on instance types:
reveal_type(sys.version_info.micro) # revealed: int
reveal_type(sys.version_info.releaselevel) # revealed: @Todo(Support for `typing.TypeAlias`)
reveal_type(sys.version_info.serial) # revealed: int
Accessing fields by index/slice
The fields of sys.version_info can be accessed by index or by slice:
import sys
reveal_type(sys.version_info[0] < 3) # revealed: Literal[False]
reveal_type(sys.version_info[1] > 9) # revealed: Literal[False]
# revealed: tuple[Literal[3], Literal[9], int, Literal["alpha", "beta", "candidate", "final"], int]
reveal_type(sys.version_info[:5])
reveal_type(sys.version_info[:2] >= (3, 9)) # revealed: Literal[True]
reveal_type(sys.version_info[0:2] >= (3, 10)) # revealed: Literal[False]
reveal_type(sys.version_info[:3] >= (3, 10, 1)) # revealed: Literal[False]
reveal_type(sys.version_info[3] == "final") # revealed: bool
reveal_type(sys.version_info[3] == "finalllllll") # revealed: Literal[False]