Fetch flask_compress version from __version__ module

[europa502]

Fix for #1606

Added code to handle "pkg_resources.DistributionNotFound: The 'flask-compress' distribution was not found and is required by the application" while building app with cx_freeze.
Since version is included only in and above cx_freeze 1.10.0, I've added the try/except condition.

[alexcjohnson]

Interesting, nice find! Unfortunately flask_compress.__version__ doesn't seem to exist until v1.10, which is probably why get_distribution was used in the first place.

I'd suggest a further fallback for the AttributeError: module 'flask_compress' has no attribute '__version__' you'll get before v1.10.0 that assumes it's maybe parse_version("1.9.0") (all that matters is >=1.6.0)

Another thing to note though: the default for compress was changed to False in Dash 2.0 (on the theory that for local dev this compression just slows things down, and for production deployments this is normally handled at a lower level like gunicorn). So this whole issue is irrelevant for most people as long as it doesn't error.

So if you're feeling adventurous, we could probably take this this whole block, plus the original from flask_compress import Compress AND the block where we use this to modify the server config:

dash/dash/dash.py

Lines 308 to 316 in b32ac95

	if (
	self.server is not None
	and not hasattr(self.server.config, "COMPRESS_ALGORITHM")
	and _flask_compress_version >= parse_version("1.6.0")
	):
	# flask-compress==1.6.0 changed default to ['br', 'gzip']
	# and non-overridable default compression with Brotli is
	# causing performance issues
	self.server.config["COMPRESS_ALGORITHM"] = ["gzip"]

and move it into the block where we actually turn compression on, so the only people who will hit any of this code will be those who explicitly enable compression, everyone else won't even import the module.

dash/dash/dash.py

Lines 453 to 455 in b32ac95

	if config.compress:
	# gzip
	Compress(self.server)

If we do this we'll just want to manually check that you actually do get gzip compression with current flask_compress

[ndrezn]

It looks like this issue was addressed independently in cx_freeze>=6.7, so closing this PR. It doesn't seem like an unreasonable change but it also doesn't appear to be a try/except we need to consider in Dash.