Fix reference linking

[Kriskras99]

I somehow messed up with my previous pull request (#3633), and I only switched back to the main repository today.

[sharkykh]

@Kriskras99 The build is failing due to the white spaces here.

[Kriskras99]

@sharkykh thanks for the pointer

[sharkykh]

I'd prefer:

if isinstance(msg.args, tuple) and msg.args[0] == 'EOPNOTSUPP':

[sharkykh]

Same:

if isinstance(msg.args, tuple) and msg.args[0] == 'EXDEV':

[labrys]

@sharkykh isinstance checks are not pythonic and should generally be avoided.

What do you intend to check here?
First of all both exceptions subclass from Exception which makes msg.args always a tuple.
Secondly the original check for is not None is equally flawed since it by default would be an empty tuple.

This should be if msg.args and msg.args[0] == 'EOPNOTSUPP':

[sharkykh]

It's used so much, how come it's not pythonic?
In any case, I agree the msg.args would always be a tuple with these exceptions.

[labrys]

@sharkykh Python is a duck-typed language and generally speaking you are breaking one of the primary advantages of Python with isinstance checks.

It can also lead to error-prone assumptions. For example what if Python 2.7.16 comes out and changes msg.args to a list instead of a tuple? The code would be broken.

The important part of the code is to check the first element of msg.args. So as long as msg.args is subscriptable and you can get the first element with msg.args[0] the code should pass, regardless of msg.args's type.

There are some legitimate reasons where an isinstance is the correct way to do something (metaclasses and abstract base classes come to mind), but usually if you need to use them you already know there isn't a cleaner way to do it.

One of the only places outside of metaclasses that I will use isinstance checks regularly is to avoid iterating a string for a function that requires an iterable as an argument. For that I usually create a helper function though to make the intent clear:

def gen_items(it):
    """
    Generate items from an iterable.

    If the iterable is a string yield it without iterating it.

    :param it: An iterable of items.
    :returns: a generator that yields items sequentially
    """
    if isinstance(it, str):
        yield it
    else:
        for item in it:
            yield item

>>> gen_items('cake')
<generator object gen_items at 0x000001F834DEADE0>

>>>list('cake')
['c', 'a', 'k', 'e']

>>> list(gen_items('cake'))
['cake']

>>> list(gen_items(['a', 1, 'cake']))
['a', 1, 'cake']

>>> list(gen_items([]))
[]

[sharkykh]

Thank you for the thorough explanation.

[labrys]

Ditto

[sharkykh]

@Kriskras99
Now you need to merge develop into this branch (or rebase) for the checks to pass.
Other than that, LGTM.