source_address in Telegram()

[farmio]

Description

• add Telegram.source_address
• use positional arguments in tests for Telegram() (i was half way through when I realized I should just move Telegram.source_address - so I finished, but I think its nicer to read anyway)

first point of #497

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• I have performed a self-review of my own code
• The documentation has been adjusted accordingly
• The changes generate no new warnings
• Tests have been added that prove the fix is effective or that the feature works
• The changes are documented in the changelog
• The Homeassistant plugin has been adjusted in case of new config options

[coveralls]

Coverage increased (+0.08%) to 94.581% when pulling 05f8764 on farmio:Telegram.source_address into 4a3718d on XKNX:master.

[marvin-w]

Works for me - tested with the telegram monitor:

Telegram received: <Telegram source_address="PhysicalAddress("1.1.37")", destination_address="GroupAddress("1/0/34")", payload="<DPTBinary value="0" />" telegramtype="TelegramType.GROUP_WRITE" direction="TelegramDirection.INCOMING" />
Telegram received: <Telegram source_address="PhysicalAddress("1.1.37")", destination_address="GroupAddress("1/0/34")", payload="<DPTBinary value="1" />" telegramtype="TelegramType.GROUP_WRITE" direction="TelegramDirection.INCOMING" />
Telegram received: <Telegram source_address="PhysicalAddress("1.1.37")", destination_address="GroupAddress("1/0/34")", payload="<DPTBinary value="0" />" telegramtype="TelegramType.GROUP_WRITE" direction="TelegramDirection.INCOMING" />
Telegram received: <Telegram source_address="PhysicalAddress("1.1.37")", destination_address="GroupAddress("1/0/34")", payload="<DPTBinary value="1" />" telegramtype="TelegramType.GROUP_WRITE" direction="TelegramDirection.INCOMING" />
Telegram received: <Telegram source_address="PhysicalAddress("1.1.37")", destination_address="GroupAddress("1/0/34")", payload="<DPTBinary value="0" />" telegramtype="TelegramType.GROUP_WRITE" direction="TelegramDirection.INCOMING" />
Telegram received: <Telegram source_address="PhysicalAddress("1.1.120")", destination_address="GroupAddress("7/0/0")", payload="<DPTBinary value="0" />" telegramtype="TelegramType.GROUP_WRITE" direction="TelegramDirection.INCOMING" />

You should also adjust https://github.com/farmio/xknx/blob/Telegram.source_address/xknx/core/value_reader.py#L51