Q:

AirFlow does not get started

According to AirFlow Offical documentation, I tried the followings
# airflow needs a home, ~/airflow is the default,
# but you can lay foundation somewhere else if you prefer
# (optional)
export AIRFLOW_HOME=~/airflow

# install from pypi using pip
pip install apache-airflow

# initialize the database
airflow initdb

# start the web server, default port is 8080
airflow webserver -p 8080

but faced with 
[2018-08-12 11:43:25,683] {__init__.py:45} INFO - Using executor SequentialExecutor
  ____________       _____________
 ____    |__( )_________  __/__  /________      __
____  /| |_  /__  ___/_  /_ __  /_  __ \_ | /| / /
___  ___ |  / _  /   _  __/ _  / / /_/ /_ |/ |/ /
 _/_/  |_/_/  /_/    /_/    /_/  \____/____/|__/

/usr/local/Cellar/python3/3.6.2/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/exthook.py:71: ExtDeprecationWarning: Importing flask.ext.cache is deprecated, use flask_cache instead.
  .format(x=modname), ExtDeprecationWarning
Traceback (most recent call last):
  File "/usr/local/bin/airflow", line 27, in <module>
    args.func(args)
  File "/usr/local/Cellar/python3/3.6.2/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/airflow/bin/cli.py", line 678, in webserver
    app = cached_app(conf)
  File "/usr/local/Cellar/python3/3.6.2/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/airflow/www/app.py", line 161, in cached_app
    app = create_app(config)
  File "/usr/local/Cellar/python3/3.6.2/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/airflow/www/app.py", line 59, in create_app
    from airflow.www import views
  File "/usr/local/Cellar/python3/3.6.2/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/airflow/www/views.py", line 29, in <module>
    import bleach
  File "/usr/local/Cellar/python3/3.6.2/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/bleach/__init__.py", line 8, in <module>
    from bleach.linkifier import (
  File "/usr/local/Cellar/python3/3.6.2/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/bleach/linkifier.py", line 7, in <module>
    from html5lib.filters.sanitizer import allowed_protocols
ImportError: cannot import name 'allowed_protocols'

A:

Try the following if you have conda:
conda install -c anaconda html5lib

If not updated html5lib using pip.

