Changes — Flask Documentation (2.0.x) : vimarsana.com

The
flask run command will only defer errors on reload. Errors
present during the initial call will cause the server to exit with
the traceback immediately. #3431
ValueError when passed an
io object in text mode. Previously, it would respond with
200 OK and an empty file. #3358
When using ad-hoc certificates, check for the cryptography library
instead of PyOpenSSL. #3492
When specifying a factory function with
FLASK APP, keyword
argument can be passed. #3553
When loading a
.env or
.flaskenv file, the current working
directory is no longer changed to the location of the file.
#3560
When returning a
(response, headers) tuple from a view, the