[Python] type hint returns NameError: name 'datetime' not defined

I have this function below;

def time_in_range(start, end, x):
"""Return true if x is in the range [start, end]"""
if start <= end:
return start <= x <= end
else:
return start <= x or x <= end


The function parameters are all datetime type. I want to add typing hint to the function. This is what I did;

def time_in_range(start: datetime, end: datetime, x: datetime) -> bool:
"""Return true if x is in the range [start, end]"""
if start <= end:
return start <= x <= end
else:
return start <= x or x <= end


I get the error NameError: name 'datetime' is not defined. What is the proper way to add typing for this function?

I am using python v3.7

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