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ruff/crates/red_knot_python_semantic/resources/mdtest/unpacking.md

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Unpacking

Tuple

Simple tuple

(a, b, c) = (1, 2, 3)
reveal_type(a)  # revealed: Literal[1]
reveal_type(b)  # revealed: Literal[2]
reveal_type(c)  # revealed: Literal[3]

Simple list

[a, b, c] = (1, 2, 3)
reveal_type(a)  # revealed: Literal[1]
reveal_type(b)  # revealed: Literal[2]
reveal_type(c)  # revealed: Literal[3]

Simple mixed

[a, (b, c), d] = (1, (2, 3), 4)
reveal_type(a)  # revealed: Literal[1]
reveal_type(b)  # revealed: Literal[2]
reveal_type(c)  # revealed: Literal[3]
reveal_type(d)  # revealed: Literal[4]

Multiple assignment

a, b = c = 1, 2
reveal_type(a)  # revealed: Literal[1]
reveal_type(b)  # revealed: Literal[2]
reveal_type(c)  # revealed: tuple[Literal[1], Literal[2]]

Nested tuple with unpacking

(a, (b, c), d) = (1, (2, 3), 4)
reveal_type(a)  # revealed: Literal[1]
reveal_type(b)  # revealed: Literal[2]
reveal_type(c)  # revealed: Literal[3]
reveal_type(d)  # revealed: Literal[4]

Nested tuple without unpacking

(a, b, c) = (1, (2, 3), 4)
reveal_type(a)  # revealed: Literal[1]
reveal_type(b)  # revealed: tuple[Literal[2], Literal[3]]
reveal_type(c)  # revealed: Literal[4]

Uneven unpacking (1)

# error: [invalid-assignment] "Not enough values to unpack (expected 3, got 2)"
(a, b, c) = (1, 2)
reveal_type(a)  # revealed: Literal[1]
reveal_type(b)  # revealed: Literal[2]
reveal_type(c)  # revealed: Unknown

Uneven unpacking (2)

# error: [invalid-assignment] "Too many values to unpack (expected 2, got 3)"
(a, b) = (1, 2, 3)
reveal_type(a)  # revealed: Literal[1]
reveal_type(b)  # revealed: Literal[2]

Starred expression (1)

# error: [invalid-assignment] "Not enough values to unpack (expected 3 or more, got 2)"
[a, *b, c, d] = (1, 2)
reveal_type(a)  # revealed: Literal[1]
# TODO: Should be list[Any] once support for assigning to starred expression is added
reveal_type(b)  # revealed: @Todo(starred unpacking)
reveal_type(c)  # revealed: Literal[2]
reveal_type(d)  # revealed: Unknown

Starred expression (2)

[a, *b, c] = (1, 2)
reveal_type(a)  # revealed: Literal[1]
# TODO: Should be list[Any] once support for assigning to starred expression is added
reveal_type(b)  # revealed: @Todo(starred unpacking)
reveal_type(c)  # revealed: Literal[2]

Starred expression (3)

[a, *b, c] = (1, 2, 3)
reveal_type(a)  # revealed: Literal[1]
# TODO: Should be list[int] once support for assigning to starred expression is added
reveal_type(b)  # revealed: @Todo(starred unpacking)
reveal_type(c)  # revealed: Literal[3]

Starred expression (4)

[a, *b, c, d] = (1, 2, 3, 4, 5, 6)
reveal_type(a)  # revealed: Literal[1]
# TODO: Should be list[int] once support for assigning to starred expression is added
reveal_type(b)  # revealed: @Todo(starred unpacking)
reveal_type(c)  # revealed: Literal[5]
reveal_type(d)  # revealed: Literal[6]

Starred expression (5)

[a, b, *c] = (1, 2, 3, 4)
reveal_type(a)  # revealed: Literal[1]
reveal_type(b)  # revealed: Literal[2]
# TODO: Should be list[int] once support for assigning to starred expression is added
reveal_type(c)  # revealed: @Todo(starred unpacking)

Starred expression (6)

# error: [invalid-assignment] "Not enough values to unpack (expected 5 or more, got 1)"
(a, b, c, *d, e, f) = (1,)
reveal_type(a)  # revealed: Literal[1]
reveal_type(b)  # revealed: Unknown
reveal_type(c)  # revealed: Unknown
reveal_type(d)  # revealed: @Todo(starred unpacking)
reveal_type(e)  # revealed: Unknown
reveal_type(f)  # revealed: Unknown

Non-iterable unpacking

# error: "Object of type `Literal[1]` is not iterable"
a, b = 1
reveal_type(a)  # revealed: Unknown
reveal_type(b)  # revealed: Unknown

Custom iterator unpacking

class Iterator:
    def __next__(self) -> int:
        return 42

class Iterable:
    def __iter__(self) -> Iterator:
        return Iterator()

(a, b) = Iterable()
reveal_type(a)  # revealed: int
reveal_type(b)  # revealed: int

Custom iterator unpacking nested

class Iterator:
    def __next__(self) -> int:
        return 42

class Iterable:
    def __iter__(self) -> Iterator:
        return Iterator()

(a, (b, c), d) = (1, Iterable(), 2)
reveal_type(a)  # revealed: Literal[1]
reveal_type(b)  # revealed: int
reveal_type(c)  # revealed: int
reveal_type(d)  # revealed: Literal[2]

String

Simple unpacking

a, b = "ab"
reveal_type(a)  # revealed: LiteralString
reveal_type(b)  # revealed: LiteralString

Uneven unpacking (1)

# error: [invalid-assignment] "Not enough values to unpack (expected 3, got 2)"
a, b, c = "ab"
reveal_type(a)  # revealed: LiteralString
reveal_type(b)  # revealed: LiteralString
reveal_type(c)  # revealed: Unknown

Uneven unpacking (2)

# error: [invalid-assignment] "Too many values to unpack (expected 2, got 3)"
a, b = "abc"
reveal_type(a)  # revealed: LiteralString
reveal_type(b)  # revealed: LiteralString

Starred expression (1)

# error: [invalid-assignment] "Not enough values to unpack (expected 3 or more, got 2)"
(a, *b, c, d) = "ab"
reveal_type(a)  # revealed: LiteralString
# TODO: Should be list[LiteralString] once support for assigning to starred expression is added
reveal_type(b)  # revealed: @Todo(starred unpacking)
reveal_type(c)  # revealed: LiteralString
reveal_type(d)  # revealed: Unknown

Starred expression (2)

(a, *b, c) = "ab"
reveal_type(a)  # revealed: LiteralString
# TODO: Should be list[Any] once support for assigning to starred expression is added
reveal_type(b)  # revealed: @Todo(starred unpacking)
reveal_type(c)  # revealed: LiteralString

Starred expression (3)

(a, *b, c) = "abc"
reveal_type(a)  # revealed: LiteralString
# TODO: Should be list[LiteralString] once support for assigning to starred expression is added
reveal_type(b)  # revealed: @Todo(starred unpacking)
reveal_type(c)  # revealed: LiteralString

Starred expression (4)

(a, *b, c, d) = "abcdef"
reveal_type(a)  # revealed: LiteralString
# TODO: Should be list[LiteralString] once support for assigning to starred expression is added
reveal_type(b)  # revealed: @Todo(starred unpacking)
reveal_type(c)  # revealed: LiteralString
reveal_type(d)  # revealed: LiteralString

Starred expression (5)

(a, b, *c) = "abcd"
reveal_type(a)  # revealed: LiteralString
reveal_type(b)  # revealed: LiteralString
# TODO: Should be list[int] once support for assigning to starred expression is added
reveal_type(c)  # revealed: @Todo(starred unpacking)

Unicode

# error: [invalid-assignment] "Not enough values to unpack (expected 2, got 1)"
(a, b) = "é"

reveal_type(a)  # revealed: LiteralString
reveal_type(b)  # revealed: Unknown

Unicode escape (1)

# error: [invalid-assignment] "Not enough values to unpack (expected 2, got 1)"
(a, b) = "\u9e6c"

reveal_type(a)  # revealed: LiteralString
reveal_type(b)  # revealed: Unknown

Unicode escape (2)

# error: [invalid-assignment] "Not enough values to unpack (expected 2, got 1)"
(a, b) = "\U0010ffff"

reveal_type(a)  # revealed: LiteralString
reveal_type(b)  # revealed: Unknown

Surrogates

(a, b) = "\ud800\udfff"

reveal_type(a)  # revealed: LiteralString
reveal_type(b)  # revealed: LiteralString

Union

Same types

Union of two tuples of equal length and each element is of the same type.

def _(arg: tuple[int, int] | tuple[int, int]):
    (a, b) = arg
    reveal_type(a)  # revealed: int
    reveal_type(b)  # revealed: int

Mixed types (1)

Union of two tuples of equal length and one element differs in its type.

def _(arg: tuple[int, int] | tuple[int, str]):
    a, b = arg
    reveal_type(a)  # revealed: int
    reveal_type(b)  # revealed: int | str

Mixed types (2)

Union of two tuples of equal length and both the element types are different.

def _(arg: tuple[int, str] | tuple[str, int]):
    a, b = arg
    reveal_type(a)  # revealed: int | str
    reveal_type(b)  # revealed: str | int

Mixed types (3)

Union of three tuples of equal length and various combination of element types:

  1. All same types
  2. One different type
  3. All different types
def _(arg: tuple[int, int, int] | tuple[int, str, bytes] | tuple[int, int, str]):
    a, b, c = arg
    reveal_type(a)  # revealed: int
    reveal_type(b)  # revealed: int | str
    reveal_type(c)  # revealed: int | bytes | str

Nested

def _(arg: tuple[int, tuple[str, bytes]] | tuple[tuple[int, bytes], Literal["ab"]]):
    a, (b, c) = arg
    reveal_type(a)  # revealed: int | tuple[int, bytes]
    reveal_type(b)  # revealed: str
    reveal_type(c)  # revealed: bytes | LiteralString

Starred expression

def _(arg: tuple[int, bytes, int] | tuple[int, int, str, int, bytes]):
    a, *b, c = arg
    reveal_type(a)  # revealed: int
    # TODO: Should be `list[bytes | int | str]`
    reveal_type(b)  # revealed: @Todo(starred unpacking)
    reveal_type(c)  # revealed: int | bytes

Size mismatch (1)

def _(arg: tuple[int, bytes, int] | tuple[int, int, str, int, bytes]):
    # error: [invalid-assignment] "Too many values to unpack (expected 2, got 3)"
    # error: [invalid-assignment] "Too many values to unpack (expected 2, got 5)"
    a, b = arg
    reveal_type(a)  # revealed: int
    reveal_type(b)  # revealed: bytes | int

Size mismatch (2)

def _(arg: tuple[int, bytes] | tuple[int, str]):
    # error: [invalid-assignment] "Not enough values to unpack (expected 3, got 2)"
    # error: [invalid-assignment] "Not enough values to unpack (expected 3, got 2)"
    a, b, c = arg
    reveal_type(a)  # revealed: int
    reveal_type(b)  # revealed: bytes | str
    reveal_type(c)  # revealed: Unknown

Same literal types

def _(flag: bool):
    if flag:
        value = (1, 2)
    else:
        value = (3, 4)

    a, b = value
    reveal_type(a)  # revealed: Literal[1, 3]
    reveal_type(b)  # revealed: Literal[2, 4]

Mixed literal types

def _(flag: bool):
    if flag:
        value = (1, 2)
    else:
        value = ("a", "b")

    a, b = value
    reveal_type(a)  # revealed: Literal[1, "a"]
    reveal_type(b)  # revealed: Literal[2, "b"]

Typing literal

from typing import Literal

def _(arg: tuple[int, int] | Literal["ab"]):
    a, b = arg
    reveal_type(a)  # revealed: int | LiteralString
    reveal_type(b)  # revealed: int | LiteralString

Custom iterator (1)

class Iterator:
    def __next__(self) -> tuple[int, int] | tuple[int, str]:
        return (1, 2)

class Iterable:
    def __iter__(self) -> Iterator:
        return Iterator()

((a, b), c) = Iterable()
reveal_type(a)  # revealed: int
reveal_type(b)  # revealed: int | str
reveal_type(c)  # revealed: tuple[int, int] | tuple[int, str]

Custom iterator (2)

class Iterator:
    def __next__(self) -> bytes:
        return b""

class Iterable:
    def __iter__(self) -> Iterator:
        return Iterator()

def _(arg: tuple[int, str] | Iterable):
    a, b = arg
    reveal_type(a)  # revealed: int | bytes
    reveal_type(b)  # revealed: str | bytes

For statement

Unpacking in a for statement.

Same types

def _(arg: tuple[tuple[int, int], tuple[int, int]]):
    for a, b in arg:
        reveal_type(a)  # revealed: int
        reveal_type(b)  # revealed: int

Mixed types (1)

def _(arg: tuple[tuple[int, int], tuple[int, str]]):
    for a, b in arg:
        reveal_type(a)  # revealed: int
        reveal_type(b)  # revealed: int | str

Mixed types (2)

def _(arg: tuple[tuple[int, str], tuple[str, int]]):
    for a, b in arg:
        reveal_type(a)  # revealed: int | str
        reveal_type(b)  # revealed: str | int

Mixed types (3)

def _(arg: tuple[tuple[int, int, int], tuple[int, str, bytes], tuple[int, int, str]]):
    for a, b, c in arg:
        reveal_type(a)  # revealed: int
        reveal_type(b)  # revealed: int | str
        reveal_type(c)  # revealed: int | bytes | str

Same literal values

for a, b in ((1, 2), (3, 4)):
    reveal_type(a)  # revealed: Literal[1, 3]
    reveal_type(b)  # revealed: Literal[2, 4]

Mixed literal values (1)

for a, b in ((1, 2), ("a", "b")):
    reveal_type(a)  # revealed: Literal[1, "a"]
    reveal_type(b)  # revealed: Literal[2, "b"]

Mixed literals values (2)

# error: "Object of type `Literal[1]` is not iterable"
# error: "Object of type `Literal[2]` is not iterable"
# error: "Object of type `Literal[4]` is not iterable"
# error: [invalid-assignment] "Not enough values to unpack (expected 2, got 1)"
for a, b in (1, 2, (3, "a"), 4, (5, "b"), "c"):
    reveal_type(a)  # revealed: Unknown | Literal[3, 5] | LiteralString
    reveal_type(b)  # revealed: Unknown | Literal["a", "b"]

Custom iterator (1)

class Iterator:
    def __next__(self) -> tuple[int, int]:
        return (1, 2)

class Iterable:
    def __iter__(self) -> Iterator:
        return Iterator()

for a, b in Iterable():
    reveal_type(a)  # revealed: int
    reveal_type(b)  # revealed: int

Custom iterator (2)

class Iterator:
    def __next__(self) -> bytes:
        return b""

class Iterable:
    def __iter__(self) -> Iterator:
        return Iterator()

def _(arg: tuple[tuple[int, str], Iterable]):
    for a, b in arg:
        reveal_type(a)  # revealed: int | bytes
        reveal_type(b)  # revealed: str | bytes