flake8 extension for mutable default arguments
Home Page: https://pypi.python.org/pypi/flake8-mutable
License: MIT License
Python's default arguments are evaluated at definition as opposed to when the function is invoked. This leads to unexpected behavior, as mutations persist between calls. For a more detailed explanation, see The Hitchhiker's Guide to Python.
def fnc(a, b={}):
pass
foo.py:2:14: M511 - mutable default arg of type Dict
pip install flake8-mutable
pytest-runner is deprecated: https://pypi.org/project/pytest-runner/
But also, as a user, I shouldn't need to install pytest-runner in order to install flake-mutable
immutables.Map from https://github.com/MagicStack/immutables currently gives a false positive for M511.
flake8-bugbear[1] includes a check for this:
B006: Do not use mutable data structures for argument defaults. They are created during function definition time. All calls to the function reuse this one instance of that data structure, persisting changes between them.
Since this repository is no longer maintained, one should consider using bugbear.
When I run flake8 with flake8-mutable it fails to provide a warning.
bash-3.2$ cat testme.py
def fnc(a, b={}):
b[a] = "hi"
print(b)
pass
fnc("a")
fnc("b")
fnc("c")
bash-3.2$ flake8 testme.py
bash-3.2$ python testme.py
{'a': 'hi'}
{'a': 'hi', 'b': 'hi'}
{'a': 'hi', 'b': 'hi', 'c': 'hi'}
bash-3.2$ flake8 --version
3.6.0 (flake-mutable: 1.2.0, mccabe: 0.6.1, pycodestyle: 2.4.0, pyflakes: 2.0.0) CPython 3.7.0 on Darwin
workaround - install flake8-bugbear instead
pip install flake8-bugbear
bash-3.2$ flake8 --version
3.6.0 (flake8-bugbear: 18.8.0, mccabe: 0.6.1, pycodestyle: 2.4.0, pyflakes: 2.0.0) CPython 3.7.0 on Darwin
bash-3.2$ flake8 testme.py
testme.py:1:14: B006 Do not use mutable data structures for argument defaults. All calls reuse one instance of that data structure, persisting changes between them.
bash-3.2$
Hey! Is there any plans to support flake8 3+ ?
Thnx
this gets picked up by the Call check, but some calls produce immutable results!
I believe the indirect assignment below should also be caught as an error:
test = {}
def test_fn(test_param=test):
pass
I haven't had a chance to look into implementation yet, but I think this would really be a great feature.
$ flake8 foo.py
main.py:2:14: M511 - mutable default arg of type Dict$ flake8 foo.py
I installed flake8-mutable 1.2.0.
$ pip install flake8-mutable
Collecting flake8-mutable
Downloading flake8-mutable-1.2.0.tar.gz (3.0 kB)
Collecting flake8
Using cached flake8-3.7.9-py2.py3-none-any.whl (69 kB)
Collecting pyflakes<2.2.0,>=2.1.0
Using cached pyflakes-2.1.1-py2.py3-none-any.whl (59 kB)
Collecting mccabe<0.7.0,>=0.6.0
Using cached mccabe-0.6.1-py2.py3-none-any.whl (8.6 kB)
Collecting entrypoints<0.4.0,>=0.3.0
Using cached entrypoints-0.3-py2.py3-none-any.whl (11 kB)
Collecting pycodestyle<2.6.0,>=2.5.0
Using cached pycodestyle-2.5.0-py2.py3-none-any.whl (51 kB)
Installing collected packages: pyflakes, mccabe, entrypoints, pycodestyle, flake8, flake8-mutable
Running setup.py install for flake8-mutable ... done
Successfully installed entrypoints-0.3 flake8-3.7.9 flake8-mutable-1.2.0 mccabe-0.6.1 pycodestyle-2.5.0 pyflakes-2.1.1And, I saved the sample code in my computer.
$ cat << EOF >> foo.py
def fnc(a, b={}):
pass
EOF
$ cat foo.py
def fnc(a, b={}):
passI tried to lint against foo.py, but I don't find the error message.
$ flake8 foo.py
$ flake8
Traceback (most recent call last):
File ".../bin/flake8", line 11, in <module>
sys.exit(main())
File ".../lib/python2.7/site-packages/flake8/main.py", line 33, in main
report = flake8_style.check_files()
File ".../lib/python2.7/site-packages/flake8/engine.py", line 181, in check_files
return self._retry_serial(self._styleguide.check_files, paths=paths)
File ".../lib/python2.7/site-packages/flake8/engine.py", line 172, in _retry_serial
return func(*args, **kwargs)
File ".../lib/python2.7/site-packages/pep8.py", line 1840, in check_files
self.input_dir(path)
File ".../lib/python2.7/site-packages/pep8.py", line 1876, in input_dir
runner(os.path.join(root, filename))
File ".../lib/python2.7/site-packages/flake8/engine.py", line 126, in input_file
return fchecker.check_all(expected=expected, line_offset=line_offset)
File ".../lib/python2.7/site-packages/pep8.py", line 1574, in check_all
self.check_ast()
File ".../lib/python2.7/site-packages/pep8.py", line 1521, in check_ast
for lineno, offset, text, check in checker.run():
File ".../lib/python2.7/site-packages/mutable_defaults.py", line 44, in run
unexplored_nodes.extend(node.body)
TypeError: 'Name' object is not iterable
$ pip freeze
flake8==2.5.4
flake8-mutable==1.0.3
mccabe==0.4.0
pep8==1.7.0
pycodestyle==2.0.0
pyflakes==1.0.0
class Container:
def __init__(self, data=[]):
self.data = data
def add(v):
self.data.append(v)
The intent in my class was that you could construct and populate in one call.
I fixed it as follows:
class Container:
def __init__(self, data=[]):
self.data = list(data) # enforce a copy
def add(v):
self.data.append(v)
but flake8 does not report the problem
React
A declarative, efficient, and flexible JavaScript library for building user interfaces.
🖖 Vue.js is a progressive, incrementally-adoptable JavaScript framework for building UI on the web.
Typescript
TypeScript is a superset of JavaScript that compiles to clean JavaScript output.
An Open Source Machine Learning Framework for Everyone
Django
The Web framework for perfectionists with deadlines.
Laravel
A PHP framework for web artisans
Bring data to life with SVG, Canvas and HTML. 📊📈🎉
JavaScript (JS) is a lightweight interpreted programming language with first-class functions.
Some thing interesting about web. New door for the world.
A server is a program made to process requests and deliver data to clients.
Machine learning is a way of modeling and interpreting data that allows a piece of software to respond intelligently.
Some thing interesting about visualization, use data art
Some thing interesting about game, make everyone happy.
Facebook
We are working to build community through open source technology. NB: members must have two-factor auth.
Microsoft
Open source projects and samples from Microsoft.
Google
Google ❤️ Open Source for everyone.
Alibaba
Alibaba Open Source for everyone
D3
Data-Driven Documents codes.
Tencent
China tencent open source team.