isempty.py

'''
AUTHOR: [email protected]
WHAT:
  This will prevent us from doing ugly shit like this
  {% if not((docker_host_tcp is undefined) or (docker_host_tcp is none) or (docker_host_tcp|trim == '')) %}
  and start being able to have a nice filter like
  {% if not(docker_host_tcp|empty) %}

DOCS:
  http://stackoverflow.com/questions/14017996/python-optional-parameter
  jinja2 folder https://github.com/pallets/jinja
  http://docs.ansible.com/ansible/dev_guide/developing_plugins.html
'''

from jinja2.runtime import Undefined

class _NO_ARG:
    def __repr__(self):
        return "<no arg>"

def custom_empty_filter(a=_NO_ARG):
    if a is _NO_ARG:
#        print ("'%s' is empty") % a
        return True
    if a is None or isinstance(a, Undefined) or a=='':
#        print ("'%s' is empty") % a
        return True
    else:
#        print ("'%s' is not empty") % a
        return False

''' Uncomment to run my tests
custom_empty_filter()
custom_empty_filter(None)
custom_empty_filter("")
custom_empty_filter('')
custom_empty_filter("None")
custom_empty_filter("Null")
custom_empty_filter("Phil")
custom_empty_filter(1)
'''

class FilterModule(object):
  def filters(self):
    return {'isempty': custom_empty_filter}