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