Fix DeprecationWarning when importing ABCs.

[mkcor]

Hi,

I'm addressing the warning I get whenever I run the tests locally:

<path>/dash/dash/development/base_component.py:265: DeprecationWarning:

Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated, and in 3.8 it will stop working

I have just transposed plotly/plotly.py#1417 to this repo.

[alexcjohnson]

Thanks @mkcor! 💃

FWIW @T4rk1n has already fixed this in dash-component-system which will replace this soon - using a slightly different syntax if six.PY2 which I think is a tiny bit nicer than try/except but that's not a big deal. https://github.com/plotly/dash-component-system/pull/1/files?file-filters%5B%5D=.cfg&file-filters%5B%5D=.in&file-filters%5B%5D=.js&file-filters%5B%5D=.json&file-filters%5B%5D=.py&file-filters%5B%5D=.txt#diff-b0f807d3cdecee9850589937afdc1dc1R25

[mkcor]

@alexcjohnson I agree that the if six.PY2 syntax is nicer. I don't have read access to https://github.com/plotly/dash-component-system but I guess the diff looks like 2ec84b7 (note: edited commit id after force-pushing on this branch; hope it's okay).

[mkcor]

Ah, of course, now pylint errors as it parses module names which are not available in Python 2.7 and vice versa. I'm curious to know how @T4rk1n handled this: via pylint config?

[alexcjohnson]

Oh that must be why he used getattr - ugh, I’d rather just silence that error (ideally only on that line)

[T4rk1n]

I used

dash/dash/_utils.py

Lines 46 to 49 in 0812b1a

	def patch_collections_abc(member):
	if six.PY2:
	return getattr(collections, member)
	return getattr(collections.abc, member)

[mkcor]

@T4rk1n Ok. I'm surprised I'm getting this:

since

dash/.pylintrc

Line 225 in 0812b1a

max-line-length=100

[mkcor]

I'm also curious because I'm not able to run pylint on this file locally: I'm getting error

RuntimeError: generator raised StopIteration
************* Module dash.development.base_component
F:  1, 0: <class 'RuntimeError'>: generator raised StopIteration (astroid-error)

[mkcor]

In the end, I silenced these pylint errors at the block level, because I noticed this was done throughout the file.
@alexcjohnson may I merge? Happy to rebase if five commits seem too much for such a small change.

[alexcjohnson]

@mkcor I hadn't noticed this before, but @T4rk1n's comment points to our util function patch_collections_abc, which is already used in this module as:

dash/dash/development/base_component.py

Line 66 in b19c2c4

class Component(patch_collections_abc('MutableMapping')):

So rather than duplicating, you could just use it again:

MutableSequence = patch_collections_abc('MutableSequence')

@T4rk1n OK I understand what you did, but would you agree it's nicer to avoid getattr if you're just passing in a constant, and simply silence the linter error with a comment? (yes, block-level is fine, I just didn't want it silenced globally in the rc file)

[T4rk1n]

would you agree it's nicer to avoid getattr if you're just passing in a constant, and simply silence the linter error with a comment?

Yes, avoid if you want auto-completion and more clarity. What I wanted to avoid was the exception based solution.

[mkcor]

@alexcjohnson oh, yes, sorry, somehow I didn't read @T4rk1n's comment carefully either!

[alexcjohnson]

💃 Thanks @mkcor!