Is this pylint error message valid or silly?

[Ben Finney]

Matthew Wilson <matt at tplus1.com> writes:

> Here's the code that I'm feeding to pylint:
> 
>     $ cat f.py
>     from datetime import datetime
> 
>     def f(c="today"):
> 
>         if c == "today":
>                     c = datetime.today()
> 
>         return c.date()
> 
> 
> And here's what pylint says:
> 
>     $ pylint -e f.py
>     No config file found, using default configuration
>     ************* Module f
>     E: 10:f: Instance of 'str' has no 'date' member (but some types could
>     not be inferred)
> 
> Is this a valid error message?

Yes. Mentally run through your code and ask “what happens if the
condition for the ‘if’ statement is false?”

> Is the code above bad? If so, what is the right way?

Yes, it's bad:

* The function name ‘f’ is completely unhelpful. Consider a reader of
  the function who has no access to the inside of your head: Your
  function should be named, preferably, as a verb phrase, to say what
  the function *does* when it is called.

* The parameter name ‘c’ is completely undescriptive. Again, consider a
  reader ignorant of your thinking: You should name parameters so they
  help the reader know what the parameter is supposed to be and how it
  will be interpreted.

* You're re-binding the parameter name ‘c’ to something different within
  the function: it starts out bound to the input string, but by the time
  the function ends you're expecting it to be bound to a datetime
  object. Instead, you should be binding a *different* name to the
  datetime object you create inside the function, and using that for the
  return statement.

-- 
 \        “Read not to contradict and confute, nor to believe and take |
  `\          for granted … but to weigh and consider.” —Francis Bacon |
_o__)                                                                  |
Ben Finney