ruff-legibility 0.2.0

Ruff-adjacent Python legibility rules for readable, reviewable code.

ruff-legibility

ruff-legibility is a Ruff-adjacent Python linter for readability and reviewability rules inspired by eslint-plugin-legibility.

Ruff does not currently load third-party rule implementations from Python packages. This package therefore runs beside Ruff and emits Ruff-style diagnostics with LEG### codes.

ruff check .
ruff-legibility check .

To keep # noqa: LEG001 comments valid when Ruff checks unused or unknown noqa codes, add LEG as an external prefix in Ruff:

[tool.ruff.lint]
external = ["LEG"]

Install

pip install ruff-legibility

For local development:

uv sync --all-groups
make check

Usage

ruff-legibility check .
ruff-legibility check src tests --output-format json
ruff-legibility check . --select LEG001,LEG002 --ignore LEG007
ruff-legibility check . --exit-zero

Default text output is intentionally close to Ruff:

example.py:4:8: LEG002 If condition has 2 boolean operators (max 0). Hoist it into a named boolean.

Configuration

Configuration can live in pyproject.toml under [tool.ruff-legibility], or in ruff-legibility.toml / .ruff-legibility.toml.

[tool.ruff-legibility]
select = ["LEG"]
extend-select = []
ignore = ["LEG007"]
extend-ignore = []
exclude = [".venv", "build", "dist"]
max-expression-operators = 4
max-if-operators = 0
max-ternary-operators = 2
max-computed-value-operators = 1
max-control-flow-depth = 3
max-array-chain-depth = 2
min-object-lookup-chain-length = 3
min-dirname-match-depth = 3

[tool.ruff-legibility.per-file-ignores]
"tests/*" = ["LEG003"]

Standalone config files omit the tool.ruff-legibility wrapper:

select = ["LEG"]
ignore = ["LEG007"]

This repository includes a ruff-legibility.toml for its own source. The default package thresholds stay stricter than the project-local development config.

Rules

Each rule has an inline dos / don'ts diff example in Examples.

Code	Rule	Default
LEG001	Limit readability operators inside a single expression.	on
LEG002	Prefer a named boolean before operator-heavy if / while conditions.	on
LEG003	Limit nested control-flow depth.	on
LEG004	Avoid complex ternary expressions.	on
LEG005	Flag likely quadratic patterns such as nested loops and repeated membership checks in loops.	on
LEG006	Avoid redundant boolean comparisons and boolean ternaries like flag == True or True if flag else False.	on
LEG007	Prefer positive condition names over names like is_not_ready.	on
LEG008	Avoid trivial wrapper functions that only forward parameters to another call.	on
LEG009	Avoid else branches after a branch that already exits.	on
LEG010	Prefer guard clauses over wrapping the main path in one large if block.	on
LEG011	Limit consecutive collection-style method chains.	on
LEG012	Prefer named values before returning computed expressions or building dict values.	on
LEG013	Avoid mutations and assignment expressions hidden inside expressions.	on
LEG014	Avoid standalone list mutation calls when an expression is clearer.	on
LEG015	Prefer explicit collection composition over starred literal unpacking.	on
LEG016	Require configured executable Python source files to start with a shebang.	on
LEG017	Prefer smoke-testing installed Python package entry points.	on
LEG018	Avoid repeated scans over the same collection in one scope.	on
LEG019	Avoid aliases that only rename another value for one use.	on
LEG020	Avoid lambdas that only forward their parameters to another callable.	on
LEG021	Prefer a flat comprehension over map followed by flattening.	on
LEG022	Avoid map/filter callbacks that keep every item unchanged.	on
LEG023	Avoid fallback expressions that only return None unchanged.	on
LEG024	Prefer set or dict lookups over long equality-or chains.	on
LEG025	Require files in named subdirectories to match the directory name.	on
LEG026	Avoid filenames that mix casing conventions.	on
LEG027	Avoid comprehensions that keep every item unchanged.	on
LEG028	Prefer comprehensions over map/filter calls with lambdas.	on
LEG029	Prefer comprehensions over simple list-building append loops.	on
LEG030	Avoid filtering the same collection with comprehensions multiple times in one scope.	on
LEG031	Avoid deep subscript chains without named intermediate values.	on
LEG032	Prefer named context when wrapping or logging broad exceptions.	on
LEG033	Avoid positive boolean names assigned from inverted expressions.	on

Examples

Removed lines are don'ts. Added lines are dos.

---

LEG001 max-expression-operators

do / don't

- return user.is_active and user.score > 10 and (user.role == "admin" or user.role == "owner")
+ is_admin = user.role == "admin"
+ is_owner = user.role == "owner"
+ has_privileged_role = is_admin or is_owner
+ return user.is_active and user.score > 10 and has_privileged_role

---

LEG002 hoist-if-operators

do / don't

- if user and user.is_active and not user.is_locked:
-     send_invite(user)
+ can_invite_user = user and user.is_active and not user.is_locked
+ if can_invite_user:
+     send_invite(user)

---

LEG003 max-control-flow-depth

do / don't

- if user:
-     for invite in invites:
-         if invite.pending:
-             while invite.retries < 3:
-                 send_invite(invite)
+ if not user:
+     return
+ pending_invites = [invite for invite in invites if invite.pending]
+ for invite in pending_invites:
+     retry_invite(invite)

---

LEG004 no-complex-ternary

do / don't

- label = "owner" if user.is_owner else "admin" if user.is_admin else "member"
+ if user.is_owner:
+     label = "owner"
+ elif user.is_admin:
+     label = "admin"
+ else:
+     label = "member"

---

LEG005 no-quadratic-patterns

do / don't

- for user in users:
-     for owner in owners:
-         if user.id == owner.user_id:
-             assign_owner(user, owner)
+ owners_by_user_id = {owner.user_id: owner for owner in owners}
+ for user in users:
+     owner = owners_by_user_id.get(user.id)
+     if owner is not None:
+         assign_owner(user, owner)

---

LEG006 no-redundant-boolean-logic

do / don't

- return True if flag == True else False
+ return flag

---

LEG007 prefer-positive-condition-names

do / don't

- is_not_ready = status != "ready"
- if is_not_ready:
+ is_ready = status == "ready"
+ if not is_ready:
      return

---

LEG008 no-trivial-wrapper-functions

do / don't

- def normalize(value):
-     return clean(value)
- result = normalize(value)
+ result = clean(value)

---

LEG009 prefer-early-return

do / don't

- if not user:
-     return None
- else:
-     return user.email
+ if not user:
+     return None
+ return user.email

---

LEG010 prefer-guard-clauses

do / don't

- if user:
-     prepare(user)
-     send_invite(user)
+ if not user:
+     return
+ prepare(user)
+ send_invite(user)

---

LEG011 max-array-chain-depth

do / don't

- users = query.filter(active=True).order_by("name").limit(10)
+ active_users = query.filter(active=True)
+ sorted_users = active_users.order_by("name")
+ users = sorted_users.limit(10)

---

LEG012 no-computed-values

do / don't

- return total + tax - discount
+ subtotal = total + tax
+ return subtotal - discount

---

LEG013 no-hidden-side-effects

do / don't

- return cache.setdefault(key, build_value())
+ if key not in cache:
+     cache[key] = build_value()
+ return cache[key]

---

LEG014 no-standalone-array-mutations

do / don't

- items.append(item)
- return items
+ return items + [item]

---

LEG015 prefer-concat-object-assign

do / don't

- payload = {**base_payload, "id": user_id}
+ payload = base_payload | {"id": user_id}

---

LEG016 require-executable-shebang

do / don't

- # scripts/report.py
- print("ok")
+ #!/usr/bin/env python3
+ print("ok")

---

LEG017 no-direct-python-bin-smoke

do / don't

- subprocess.run(["python", "src/example/cli.py", "--help"], check=True)
+ subprocess.run(["example", "--help"], check=True)

---

LEG018 no-repeated-collection-search

do / don't

- if user_id in ids and owner_id in ids:
-     return True
+ id_lookup = set(ids)
+ required_ids = {user_id, owner_id}
+ return required_ids.issubset(id_lookup)

---

LEG019 no-single-use-renaming-alias

do / don't

- current_user = request.user
- return current_user.email
+ return request.user.email

---

LEG020 no-unnecessary-lambda

do / don't

- users = sorted(users, key=lambda user: normalize(user))
+ users = sorted(users, key=normalize)

---

LEG021 prefer-flat-comprehension

do / don't

- values = list(chain.from_iterable(map(expand, items)))
+ values = [value for item in items for value in expand(item)]

---

LEG022 no-identity-array-callback

do / don't

- names = list(map(lambda name: name, names))
+ names = list(names)

---

LEG023 no-redundant-none-fallback

do / don't

- return value if value is not None else None
+ return value

---

LEG024 prefer-object-lookup

do / don't

- if status == "new" or status == "open" or status == "pending":
-     queue_item(item)
+ if status in {"new", "open", "pending"}:
+     queue_item(item)

---

LEG025 require-filename-matches-dirname

do / don't

- src/billing/customer/profile.py
+ src/billing/customer/customer.py

---

LEG026 no-mixed-filename-casing

do / don't

- user_Profile.py
+ user_profile.py

---

LEG027 no-identity-comprehension

do / don't

- copied = [item for item in items]
+ copied = list(items)

---

LEG028 prefer-comprehension-over-map-filter

do / don't

- names = list(map(lambda user: user.name, users))
+ names = [user.name for user in users]

---

LEG029 no-loop-append-comprehension

do / don't

- names = []
- for user in users:
-     names.append(user.name)
+ names = [user.name for user in users]

---

LEG030 no-repeated-comprehension-filter

do / don't

- active_users = [user for user in users if user.active]
- admin_users = [user for user in users if user.is_admin]
+ filtered_users = [user for user in users if user.active or user.is_admin]
+ active_users = [user for user in filtered_users if user.active]
+ admin_users = [user for user in filtered_users if user.is_admin]

---

LEG031 no-deep-subscript-chain

do / don't

- return payload["user"]["profile"]["email"]
+ user = payload["user"]
+ profile = user["profile"]
+ return profile["email"]

---

LEG032 prefer-named-exception-context

do / don't

- except Exception as error:
-     raise RuntimeError(error)
+ except Exception as error:
+     message = "Failed to load user profile"
+     raise RuntimeError(message) from error

---

LEG033 no-boolean-parameter-name-drift

do / don't

- is_ready = status != "ready"
+ is_ready = status == "ready"

Pre-commit

repos:
  - repo: local
    hooks:
      - id: ruff-legibility
        name: ruff-legibility
        entry: ruff-legibility check
        language: system
        types: [python]

Development

Common commands:

uv sync --all-groups
uv run ruff check .
uv run ruff-legibility check src tests
uv run pytest
uv build

Release builds should use:

uv build --no-sources

Publishing is configured for PyPI Trusted Publishing:

uv publish