flake8-plone-hasattr 1.1.1

Flake8 Plone hasattr plugin

Python standard hasattr is considered harmful (within Plone projects).

The (hidden) problem with hasattr is that it swallows exceptions, which in your normal business logic you really don’t want to.

Specially in Plone context that could mean swallowing a database error, or a permission exception, etc.

Take, for instance, the following code:

>>> class Foo(object):
...     @property
...     def my_attr(self):
...         raise ValueError('nope, nope, nope')
...
>>> bar = Foo()
>>> bar.my_attr
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 4, in my_attr
ValueError: nope, nope, nope
>>> hasattr(Foo, 'my_attr')
True
>>> hasattr(bar, 'my_attr')
False

One should rather do:

>>> getattr(bar, 'my_attr', None)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 4, in my_attr
ValueError: nope, nope, nope

Or in case you want to handle an exception:

>>> try:
...     value = getattr(bar, 'my_attr', None)
... exception ValueError:
...     value = None

This plugin is based on a python checker that was in plone.recipe.codeanalysis.

$ pip install flake8-plone-hasattr