Hello,
I had a dict that saved a date for each symbol:

self.future_dates[symbol] = (date + timedelta(days=360))

But each time it passes through the loop it takes the new value and deletes the old one. My idea is to have for each symbol 3 dates.

Normally I would just append the values but that trows the error.

self.future_dates[symbol].append(date + timedelta(days=360))

 

The code which it is in is as follows:

for symbol in [x.Symbol for x in changes.AddedSecurities]:
	for date in a:
		self.future_dates[symbol].append(date + timedelta(days=360))
Error:
Runtime Error: Trying to retrieve an element from a collection using a key that does not exist in that collection throws a KeyError exception. To prevent the exception, ensure that the key exist in the collection and/or that collection is not empty.
  at OnSecuritiesChanged
    self.future_dates[symbol].extend((date + timedelta(days=360)))
   at Python.Runtime.PythonException.ThrowLastAsClrException()
   at Python.Runtime.PyObject.Invoke(PyTuple args in main.py: line 82 (Open Stack Trace)

 

Does anyone has an idea how to solve this problem?

Thanks in advance!