rabbitinspect 0.2.0

Python code performance analyzer written in Rust — detects unused variables, None comparisons, list vs generator, and more

rabbitinspect

A Python code performance analyzer written in Rust (via PyO3). It scans your Python source code and points out patterns that can be made faster, more memory-efficient, or more idiomatic — with optional automatic fixes.

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Installation

pip install rabbitinspect

The package ships pre-compiled wheels — no Rust toolchain required.

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Usage

CLI

# Check a single file
rabbitinspect file.py

# Check an entire directory
rabbitinspect src/

# Auto-fix detected issues
rabbitinspect file.py --fix

# Select specific checks only
rabbitinspect file.py --select RAB002,RAB003

# Ignore specific checks
rabbitinspect file.py --ignore RAB022,RAB101

# JSON output
rabbitinspect file.py --format json

# Disable colored output
rabbitinspect file.py --no-color

Output (ruff-style):

file.py:10:5: RAB002 Use 'is' instead of '==' for None comparison
file.py:25:8: RAB003 Use 'not x' instead of 'len(x) == 0' for emptiness check

Suppress checks inline:

x = 42  # noqa: RAB067
try:
    pass
except:
    pass  # noqa: RAB012, RAB013

Configuration via pyproject.toml

[tool.rabbitinspect]
select = ["RAB002", "RAB003", "RAB006"]
ignore = ["RAB022", "RAB101"]

Python API

from rabbitinspect import analyze_code, apply_fixes

source = """
def foo(x):
    if x == None:
        return True
    return False
"""

findings = analyze_code(source)
for f in findings:
    print(f"{f['code']}:{f['line']}:{f['col']} {f['message']}")

# Apply fixes
fixes = [f['fix'] for f in findings if f.get('fix')]
fixed = apply_fixes(source, fixes)

---

Checks

Code	Check	Auto-fix
RAB001	Variable assigned but never used	❌
RAB002	x == None instead of x is None	✅
RAB003	len(x) == 0 instead of not x	✅
RAB004	any([...]) / all([...]) with list comprehension	✅
RAB005	for k in d.keys() instead of for k in d	✅
RAB006	type(x) == T instead of isinstance(x, T)	✅
RAB007	Unnecessary else after return/raise/break/continue	✅
RAB008	for i in range(len(x)) instead of enumerate(x)	❌
RAB009	String concatenation in a loop (s += str(x))	❌
RAB010	set(list(x)) — unnecessary list() call	❌
RAB011	Mutable default argument (x=[], x={})	❌
RAB012	Bare except: clause	❌
RAB013	Bare except: pass	❌
RAB014	class Foo(object) in Python 3	❌
RAB015	k in d.keys() instead of k in d	✅
RAB016	.format() instead of f-string	❌
RAB017	Function too long (> 30 statements)	❌
RAB018	Too many parameters (> 6)	❌
RAB019	os.system() instead of subprocess.run()	❌
RAB020	time.time() for benchmarking	❌
RAB022	Public function missing return type hint	❌
RAB023	Redundant .call() method call	❌
RAB024	Deep comprehension (> 2 nested for clauses)	❌
RAB025	Long if-elif chain (> 3 branches)	❌
RAB026	sorted(list(x)) / reversed(tuple(x)) — redundant collection	✅
RAB029	x == True / x == False instead of x / not x	✅
RAB030	if cond: return True else: return False → return cond	✅
RAB031	if k in d: return d[k] → d.get(k)	✅
RAB032	bool(x) inside a boolean context	✅
RAB034	assert True / assert False	✅
RAB035	x[:] → x.copy() for list copies	✅
RAB036	x**2 / x**3 → x * x / x * x * x	✅
RAB037	map(lambda, ...) / filter(lambda, ...)	✅
RAB038	x in [const, ...] → x in {const, ...}	✅
RAB039	List[X] / Dict[K,V] → list[X] / dict[K,V]	✅
RAB040	@dataclass without slots=True	✅
RAB041	re.compile() inside a function	❌
RAB042	for line in f.readlines() → for line in f	✅
RAB043	Manual for loop with .append() instead of comprehension	❌
RAB044	Optional[X] / Union[A, B] → X | None / A | B	✅
RAB045	open() without context manager (with)	❌
RAB046	sorted(x)[0] → min(x)	✅
RAB047	sorted(x)[-1] → max(x)	✅
RAB048	not x is None → x is not None	✅
RAB049	x = x + 1 → x += 1	✅
RAB050	for i in range(len(seq)) — iterate directly	❌
RAB051	d.setdefault(k, []).append(v) → defaultdict	❌
RAB052	type(x) == A or type(x) == B → isinstance(x, (A, B))	✅
RAB053	x is True / x is False → x / not x	✅
RAB054	if not x: x = y → x = x or y	✅
RAB055	Unused loop variable → _	✅
RAB056	Nested with statements	❌
RAB057	s.startswith('a') or s.startswith('b') → s.startswith(('a', 'b'))	✅
RAB058	return True if cond else False → return cond	✅
RAB059	while True: without break → infinite loop	❌
RAB060	sorted(x).sort() → x.sort()	✅
RAB061	from module import * — wildcard import	❌
RAB062	Redundant pass after docstring	✅
RAB063	x is 5 / x is "str" → x == 5 / x == "str"	✅
RAB064	__init__ returning non-None value	✅
RAB065	if True: / if False: dead code	❌
RAB066	Function definition inside a loop	❌
RAB067	Variable/function shadows built-in name	✅
RAB068	raise Exc() without from inside except	❌
RAB069	dict() / list() / tuple() → {} / [] / ()	✅
RAB070	x == "" / x == [] / x == {} → not x / x	✅
RAB071	List comp inside str.join() → generator	✅
RAB072	Except handler only re-raises	❌
RAB073	Old-style % string formatting	❌
RAB074	os.path.* → pathlib.Path	❌
RAB075	isinstance(x, (A,)) → isinstance(x, A)	✅
RAB076	str() on value already a string	✅
RAB078	except Exception: pass — silent swallow	❌
RAB079	__del__ method defined	❌
RAB080	list(d.keys()) / list(d.values()) → list(d)	✅
RAB083	Nested ternary expression	❌
RAB085	reversed(sorted(x)) → sorted(x, reverse=True)	✅
RAB087	{k: v for k, v in zip(...)} → dict(zip(...))	✅
RAB088	while len(x) > 0 → while x	✅
RAB089	copy.copy(x) → x.copy()	✅
RAB101	Cyclomatic complexity > 10	❌
RAB102	Cognitive complexity > 15	❌

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Performance rationale

Why Rust?

Parsing and analyzing Python source is a CPU-bound operation. Rust's zero-cost abstractions and lack of a garbage collector make it ideal for this kind of static analysis. The core engine uses rustpython-parser to build a full AST and walks it with pattern matching — all without any Python overhead at analysis time.

Specific improvements

Pattern	Inefficiency	Fix
x == None	Calls x.__eq__(None), may be overridden	x is None — direct pointer comparison
any([x for x in items])	Builds full list in memory	any(x for x in items) — generator yields one at a time
len(x) == 0	Calls x.__len__(), may be O(n)	not x — uses __bool__ protocol
for k in d.keys()	Creates a dict_keys view object	for k in d: — iterates dict directly
type(x) == T	Ignores subclass relationships	isinstance(x, T) — correct for inheritance
for i in range(len(x))	Double lookup x[i] overhead	for i, item in enumerate(x)
s += str(x) in loop	O(n²) string allocations	"".join(...) — single allocation
set(list(x))	Intermediate list allocation	set(x) — builds directly from iterator
k in d.keys()	Creates view for membership test	k in d — direct hash lookup
sorted(list(x))	Intermediate list before sort	sorted(x) — sorts iterable directly
if k in d: return d[k]	Two dict lookups	return d.get(k) — single lookup
x[:] for list copy	Slice intent unclear	x.copy() — explicit intent
sorted(x)[0]	O(n log n) sort for min	min(x) — O(n) single pass
sorted(x)[-1]	O(n log n) sort for max	max(x) — O(n) single pass
List[int] / Dict[str, int]	Requires typing import	list[int] / dict[str, int] — Python 3.9+
for line in f.readlines()	Loads entire file into memory	for line in f — line by line, O(1) memory
d.setdefault(k, []).append(v)	Creates default on every call	defaultdict(list) — default only on missing key
type(x) == A or type(x) == B	Multiple type() calls	isinstance(x, (A, B)) — single check
reversed(sorted(x))	Two passes over data	sorted(x, reverse=True) — single pass
{k: v for k, v in zip(...)}	Comprehension overhead	dict(zip(...)) — direct constructor

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Development

# Setup
git clone https://github.com/rroblf01/rabbitinspect
cd rabbitinspect

# Build the Rust extension (requires Rust toolchain)
cargo build --release
cp target/release/librabbitinspect.so python/rabbitinspect/_core.cpython-314-x86_64-linux-gnu.so

# Run tests
uv run pytest tests/

# Build distributable wheels
uv run maturin build

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License

MIT