python: flake8 cannot find non exising method

Question

If I do something like:

new_list = []
new_list.foo()

flake8 does not return an error for foo() method since it is not a 'list' method.

Is this normal or do I need to configure something?

Answer 1

Flake8 is a wrapper around these tools:

• PyFlakes
• pep8
• Ned Batchelder’s McCabe script

PyFlakes is the part that you might expect to detect this type of error. But it detects very little, and it explains why:

Pyflakes is also faster than Pylint or Pychecker. This is largely because Pyflakes only examines the syntax tree of each file individually. As a consequence, Pyflakes is more limited in the types of things it can check.

The flake8 docs list the error codes provided by Pyflakes:

code    sample message
F401    module imported but unused
F402    import module from line N shadowed by loop variable
F403    ‘from module import *’ used; unable to detect undefined names
F404    future import(s) name after other statements
F811    redefinition of unused name from line N
F812    list comprehension redefines name from line N
F821    undefined name name
F822    undefined name name in __all__
F823    local variable name ... referenced before assignment
F831    duplicate argument name in function definition
F841    local variable name is assigned to but never used

I second the recommendation for PyCharm, followed by PyLint.

Answer 2

flake8 does not handle the problem, but PyLint does - issues the no-member warning:

$ pylint test.py
No config file found, using default configuration
************* Module test
C:  1, 0: Missing module docstring (missing-docstring)
C:  1, 0: Invalid constant name "new_list" (invalid-name)
E:  2, 0: Instance of 'list' has no 'foo' member (no-member)

And, the built-in to PyCharm code analyzer would also warn about the unresolved attribute: