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ruff/crates/red_knot_python_semantic/resources/mdtest/subscript/bytes.md
David Peter 56c796acee
[red-knot] Slice expression types & subscript expressions with slices (#13917) 
## Summary

- Add a new `Type::SliceLiteral` variant
- Infer `SliceLiteral` types for slice expressions, such as
`<int-literal>:<int-literal>:<int-literal>`.
- Infer "sliced" literal types for subscript expressions using slices,
such as `<string-literal>[<slice-literal>]`.
- Infer types for expressions involving slices of tuples:
`<tuple>[<slice-literal>]`.

closes #13853

## Test Plan

- Unit tests for indexing/slicing utility functions
- Markdown-based tests for
  - Subscript expressions `tuple[slice]`
  - Subscript expressions `string_literal[slice]`
  - Subscript expressions `bytes_literal[slice]`
2024-10-29 10:17:31 +01:00

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Bytes subscripts

Indexing

b = b"\x00abc\xff"

reveal_type(b[0])  # revealed: Literal[b"\x00"]
reveal_type(b[1])  # revealed: Literal[b"a"]
reveal_type(b[4])  # revealed: Literal[b"\xff"]

reveal_type(b[-1])  # revealed: Literal[b"\xff"]
reveal_type(b[-2])  # revealed: Literal[b"c"]
reveal_type(b[-5])  # revealed: Literal[b"\x00"]

reveal_type(b[False])  # revealed: Literal[b"\x00"]
reveal_type(b[True])  # revealed: Literal[b"a"]

x = b[5]  # error: [index-out-of-bounds] "Index 5 is out of bounds for bytes literal `Literal[b"\x00abc\xff"]` with length 5"
reveal_type(x)  # revealed: Unknown

y = b[-6]  # error: [index-out-of-bounds] "Index -6 is out of bounds for bytes literal `Literal[b"\x00abc\xff"]` with length 5"
reveal_type(y)  # revealed: Unknown

def int_instance() -> int:
    return 42

a = b"abcde"[int_instance()]
# TODO: Support overloads... Should be `bytes`
reveal_type(a)  # revealed: @Todo

Slices

b = b"\x00abc\xff"

reveal_type(b[0:2])  # revealed: Literal[b"\x00a"]
reveal_type(b[-3:])  # revealed: Literal[b"bc\xff"]

b[0:4:0]  # error: [zero-stepsize-in-slice]
b[:4:0]  # error: [zero-stepsize-in-slice]
b[0::0]  # error: [zero-stepsize-in-slice]
b[::0]  # error: [zero-stepsize-in-slice]

def int_instance() -> int: ...

byte_slice1 = b[int_instance() : int_instance()]
# TODO: Support overloads... Should be `bytes`
reveal_type(byte_slice1)  # revealed: @Todo

def bytes_instance() -> bytes: ...

byte_slice2 = bytes_instance()[0:5]
# TODO: Support overloads... Should be `bytes`
reveal_type(byte_slice2)  # revealed: @Todo