Allow iteration in python_script

[balloob]

Description:

This will allow us to iterate inside Python scripts and thus also use for-loops.

Example python_script

home = 0
for entity_id in hass.states.entity_ids('device_tracker'):
    state = hass.states.get(entity_id)
    if state.state == 'home':
        home = home + 1

hass.states.set('sensor.people_home', home, {
    'unit_of_measurement': 'people',
    'friendly_name': 'People home'
})

Checklist:

If the code does not interact with devices:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• Tests have been added to verify that the new code works.

[balloob]

Cherry-picked for 0.47.1

[azogue]

Hi @balloob,

I'm playing with the new component (in 0.47.1) and I have noticed certain lacks related to this entry, I don't know if they are intended:

• No hass object for comprehensions (NameError: name 'hass' is not defined)

# Not working:
local_data = {k: hass.states.get(k) for k in local_data.keys()}

# Working:
for k in local_data.keys():
    local_data[k] = hass.states.get(k)

• No key-access to dicts (NameError: name '_getitem_' is not defined):
  close_house = local_data['input_boolean.close_house']
• No getattr (NameError: name 'getattr' is not defined):
  close_house = getattr(local_data, 'input_boolean.close_house')

This is working:
close_house = local_data.get('input_boolean.close_house')

• No vars starting with '_': Error loading script testing.py: Line 2: "_variable_name" is an invalid variable name because it starts with "_"

• Can't use max: NameError: name 'max' is not defined

• Can't import anything: ImportError: __import__ not found

Do you want me to publish these as a new issue?

[balloob]

Please don't use PRs to report issues. Have a look here: https://community.home-assistant.io/t/python-script-feedback/20186