Errors

Errors caused by Bluetooth or by the other device all derive from RfcommError, so one except catches them all:

try:
    ...
except aio_rfcomm.errors.RfcommError as error:
    print(f"{type(error).__name__}: {error}")

Errors caused by mistakes in your own code are RuntimeError or ValueError instead, so catching RfcommError never hides a bug. The library's own errors are all in aio_rfcomm.errors.

Bluetooth cannot be used

BluetoothUnavailableError means Bluetooth cannot be used right now. Its reason says why, as an Availability. See Bluetooth for what each reason means and what the user can do about it.

Connecting

Error	Means
DeviceNotFoundError	The device did not answer. It may be switched off or out of range. Its address says which device.
ServiceNotFoundError	The device does not offer that service, or refused that channel number. See also Platforms.
ConnectionFailedError	The channel could not be opened, or the service could not be published.

While connected

ChannelClosedError means the connection has ended: the other device hung up, or the connection to it was lost. To find out whether the device is still there, open a channel again. DeviceNotFoundError then means it is switched off or out of range.

Once a connection has ended, and any bytes that arrived before the end have been received, every call to receive and send raises the same error. If the connection ended because Bluetooth stopped being usable, they raise BluetoothUnavailableError instead.

DelimiterNotFoundError means receive_until found no delimiter within max_bytes.

Limits

Error	Means
ChannelInUseError	The channel you asked to serve on is already in use.
UnsupportedOperationError	This platform cannot do that, or not right now. The message says what to do instead.

Mistakes in your code

These are RuntimeError, not RfcommError.

Error	Means
RuntimeError	A connection request was accepted or declined twice.
BusyResourceError	Two tasks received at the same time on one channel, or two tasks sent.
ScopeClosedError	Something was used after its async with block ended.
BluetoothAlreadyOpenError	Bluetooth was opened while it was already open.

A channel number outside 1 to 30, or a string that is not a Bluetooth address, raises ValueError.

Next: Platforms, for where Linux, macOS and Windows differ.