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This document attempts to document all codemods that shed does.

leave_Assert

Remove redundant assert x where x is a literal that always evaluate to True.
Replace assert y where y is a literal that always evaluates to False.

Examples

input

# truthy statements removed, with corresponding comments
assert True
assert "message"  # rip
assert (1, 2)

# false statements replaced with raise AssertionError
assert None
assert ""
assert 0, "hello"

assert False, "this is the only case handled by ruff"

output

# false statements replaced with raise AssertionError
raise AssertionError
raise AssertionError
raise AssertionError("hello")

raise AssertionError("this is the only case handled by ruff")

Full test data in tests/recorded/asserts.txt

Ruff supports autofixing B011, but that only covers the precise case of exactly replacing assert False with raise AssertionError.

remove_pointless_parens_around_call

Removes pointless parentheses wrapping a call. Ruff has UP034, but that only handles a subset of the cases shed handles.

Examples

Full test data in tests/recorded/parens.txt and tests/recorded/parens_with_comment.txt

input

(list("abc"))
(["foo"].append("bar"))
(["foo"].append("bar"))
foo((list("abc")))  # only one handled by ruff

# handled by the codemod after shed runs black on it
(
    []
    .append(1)
)

output

list("abc")
["foo"].append("bar")
["foo"].append("bar")
foo(list("abc"))  # only one handled by ruff

# handled by the codemod after shed runs black on it
[].append(1)

replace_unnecessary_nested_calls

Resolves flake8-comprehension C414. Ruffs implementation currently breaks sorting stability in one case.

Examples

Full test data in tests/recorded/comprehensions/C414.txt

input

list(tuple(iterable))
set(reversed(iterable))
sorted(reversed(iterable))  # unsafe to fix, but ruff does

# cases handled by our codemod, but not by ruff
sorted(sorted(iterable, reverse=True))
sorted(sorted(iterable), reverse=True)
sorted(sorted(iterable, reverse=True), reverse=False)
sorted(sorted(iterable, reverse=False), reverse=True)

# unsafe to fix, even if both have the same key function (it might have side-effects)
sorted(sorted(iterable), key=int)
sorted(sorted(iterable, key=bool))
sorted(sorted(iterable, key=bool), key=int)
sorted(sorted(iterable, key=bool), key=bool)

output

list(iterable)
set(iterable)
sorted(reversed(iterable))  # unsafe to fix, but ruff does

# cases handled by our codemod, but not by ruff
sorted(iterable)
sorted(iterable, reverse=True)
sorted(iterable, reverse=False)
sorted(iterable, reverse=True)

# unsafe to fix
sorted(sorted(iterable), key=int)
sorted(sorted(iterable, key=bool))
sorted(sorted(iterable, key=bool), key=int)
sorted(sorted(iterable, key=bool), key=bool)

replace_unnecessary_subscript_reversal

Fix flake8-comprehensions C415.

Unnecessary subscript reversal of iterable within [reversed/set/sorted](). ruff does not support autofixing of C415

input

set(iterable[::-1])
sorted(iterable[::-1])
reversed(iterable[::-1])

set(iterable[None:])
set(iterable[:None:1])
set(iterable[None:None:])

output

set(iterable)
sorted(iterable)
reversed(iterable)

set(iterable)
set(iterable)
set(iterable)

reorder_union_literal_contents_none_last

Puts None last in a subscript of Union or Literal

Test data in tests/recorded/flatten_literal.txt and tests/recorded/reorder_none.txt

input

def g(x: Union[None, float] = None):
    pass


var3: Optional[None, int, float]
foo: set[None, int]

output

def g(x: Union[int, None] = None):
    pass


var3: Optional[int, float, None]
foo: set[int, None]

reorder_merge_optional_union

Turn Union[..., None] into Optional[Union[...]].

Test data in tests/recorded/flatten_union.txt

input

Union[int, str, None]
Union[int, None, str]

output

Optional[Union[int, str]]
Optional[Union[int, str]]

reorder_union_operator_contents_none_last

Reorders binary-operator type unions to have None last.

Test data in tests/recorded/union_op_none_last.txt

input

None | int  # not a type annotation
var: None | int
var2: bool | None | float
var3: float | None | bool

output

None | int  # not a type annotation
var: int | None
var2: bool | float | None
var3: float | bool | None

[Not Implemented] sort union types

Fully sort types in union/optional, so as to standardize their ordering and make it easier to see if two type annotations are in fact the same. This was never implemented, it was deemed to controversial as shed does not allow disabling specific checks, but may be of interest to ruff.

input

k: Union[int, float]
l: Union[int, float]
m: float | bool
n: Optional[str, MyOtherType, bool]

output

k: Union[float, int]
l: Union[float, int]
m: bool | float
n: Optional[MyOtherType, bool, str]

flatten_literal_subscript

Flattens a Literal inside a Literal.

Test data in tests/recorded/flatten_literal.txt

input

Literal[1, Literal[2, 3]]

output

Literal[1, 2, 3]

flatten_union_subscript

Flattens an Optional/Union inside a Union.

Test data in tests/recorded/flatten_literal.txt

input

Union[int, Optional[str], bool]
Union[int, Optional[str], None]
Union[Union[int, float], str]
Union[int, Literal[1, 2]]  # this should not change
Union[int, Literal[1, 2], Optional[str]]
Union[int, str, None]

output

Union[int, str, bool, None]
Union[int, str, None]
Union[int, float, str]
Union[int, Literal[1, 2]]  # this should not change
Union[int, Literal[1, 2], str, None]
Union[int, str, None]

discard_empty_else_blocks

An else: pass block can always simply be discarded. This should also remove else: ... blocks but that's not currently supported.

Test data in tests/recorded/empty-else.txt

input

if foo:
    ...
else:
    pass

while foo:
    ...
else:
    pass

for _ in range(10):
    ...
else:
    pass

try:
    1 / 0
except Exception:
    ...
else:
    pass

if foo:
    ...
else:
    ...

output

if foo:
    ...

while foo:
    ...

for _ in range(10):
    ...

try:
    1 / 0
except Exception:
    ...

if foo:
    ...
else:  # should ideally be removed
    ...

remove_lambda_indirection

Removes useless lambda wrapper.

Test data in tests/recorded/lambda-unwrapping.txt

input

lambda: self.func()
lambda x: foo(x)
lambda x, y, z: (t + u).math_call(x, y, z)

output

self.func
foo
(t + u).math_call

split_assert_and

Split assert a and b into assert a and assert b. This is supported by ruff, but we have much more sophisticated handling of comments.

Test data in tests/recorded/split_assert.txt

remove_unnecessary_call_*

Removes unnecessary len/bool calls in tests, autofixes PIE787.

No check for this in ruff; SIM103 needless-bool is specifically about returns.

Test data in tests/recorded/pie788_no_bool.txt and tests/recorded/pie788_no_len.txt

input

if len(foo):
    ...
while bool(foo):
    ...
print(5 if len(foo) else 7)

output

if foo:
    ...
while foo:
    ...
print(5 if foo else 7)

split_nested_with

Ruff does this, but only if it wouldn't turn it into a multi-line with.

input

with make_context_manager(1) as cm1:
    with make_context_manager(2) as cm2:
        pass
    # Preserve this comment

with make_context_manager(1) as cm1, make_context_manager(2) as cm2:
    with make_context_manager(3) as cm3:
        pass

with make_context_manager(1) as cm1:
    with make_context_manager(2) as cm2:
        with make_context_manager(3) as cm3:
            with make_context_manager(4) as cm4:
                pass

output

with make_context_manager(1) as cm1, make_context_manager(2) as cm2:
    pass
    # Preserve this comment

with (
    make_context_manager(1) as cm1,
    make_context_manager(2) as cm2,
    make_context_manager(3) as cm3,
):
    pass

with (
    make_context_manager(1) as cm1,
    make_context_manager(2) as cm2,
    make_context_manager(3) as cm3,
    make_context_manager(4) as cm4,
):
    pass

replace_builtin_empty_collection [removed]

A codemod that was removed in favor of ruffs C406/C409/C410/C418, but that also covered some cases that ruff currently raises no errors for.

input

# handled by ruff
list([])  # C410
list(())  # C410

dict({})  # C418
dict([])  # C406
dict(())  # C406

tuple([])  # C409
tuple(())  # C409

# not handled by ruff, but was handled by our codemod
list({})
list("")
dict("")
tuple({})
tuple("")

output

# handled by ruff
[]  # C410
[]  # C410

{}  # C418
{}  # C406
{}  # C406

()  # C409
()  # C409

# not handled by ruff, but was handled by our codemod
[]
[]
{}
()
()