I am writing a test algo in Python and after making some changes in another function, my history call (Last line of my code below) stopped working all of a sudden.  I get the error: 

BacktestingRealTimeHandler.Run(): There was an error in a scheduled event EveryDay: 12. The error was NameError : name 'timedelta' is not defined

 

I am not a programmer just a hobbiest but I can't figure out why this error would be happening all of sudden?

Here is my code.

import numpy as np

### <summary>
### Basic template algorithm simply initializes the date range and cash. This is a skeleton
### framework you can use for designing an algorithm.
### </summary>


class BasicTemplateAlgorithm(QCAlgorithm):
'''Basic template algorithm simply initializes the date range and cash'''

def Initialize(self):
'''Initialise the data and resolution required, as well as the cash and start-end dates for your algorithm. All algorithms must initialized.'''
#some Globals
#stock="SPY"
#bond="BNDX"
#setting our benchmark aginst the SPY Ticker
self.SetBenchmark("SPY")
#Set Dates for backtesting
self.SetStartDate(2019,1,1) #Set Start Date
self.SetEndDate(2019,1,10) #Set End Date
self.SetCash(100000) #Set Strategy Cash
# Find more symbols here: http://quantconnect.com/data
# Not sure if these need to be assigned to the variables or not but it started working once I assigned them to variables? They aren't referenced anywhere else.
stockEquity=self.AddEquity("SPY", Resolution.Daily)
#bondEquity=self.AddEquity(bond, Resolution.Daily)
self.Schedule.On(self.DateRules.EveryDay(), self.TimeRules.At(12,0), self.HelloWorldDaily)

def OnData(self, data):
pass

def HelloWorldDaily(self):

slices = self.History(["SPY"], timedelta(7))