ForecastingModel.backtest() fails if forecast_horizon isn't provided

[LeoTafti]

darts/darts/models/forecasting_model.py

Lines 148 to 157 in 2977f4f

	if hasattr(n, 'forecast_horizon'):
	raise_if_not(n.forecast_horizon > 0, 'The provided forecasting horizon must be a positive integer.', logger)
	# check start parameter
	if hasattr(n, 'start'):
	if isinstance(n.start, float):
	raise_if_not(n.start >= 0.0 and n.start < 1.0, '`start` should be between 0.0 and 1.0.', logger)
	elif isinstance(n.start, pd.Timestamp):
	if (hasattr(n, 'trim_to_series') and n.trim_to_series) or not hasattr(n, 'trim_to_series'):
	raise_if_not(n.start + training_series.freq() * n.forecast_horizon in training_series,

n.forecast_horizon at line 157 fails when hasattr(n, 'forecast_horizon') == false, ie. every time no explicit value is passed when calling backtest()

Error produced:

AttributeError: 'types.SimpleNamespace' object has no attribute 'forecast_horizon'

[LeoTafti]

I'm sure how to go about fixing it, since performing the check on line 157 requires to know forecast_horizon value, but we don't have it in _backtest_sanity_checks when the call to backtest() didn't specify it and used the default value…