Python Key error -when trying to use statements - python-3.x

Question

Here is my code i am getting a key error on line 31, something to do with the word 'Reserved'
#Create a loan class that will allow members to borrow books
class Loan(Book, Member):
"""Class that allows members to reserve,cancel reservations, return and borrow books
Librarians can extract the data
pre-conditions: inherits from Book and member classes
if the above is not correct the data wont be
"""
#classmethod
#set up a class in order to borrow a book
def Borrow(cls, name, title):
"""
Parameters
----------
cls : TYPE
"""
#Find ID of book/member
BookID = Book.scan(title)[0]
MemberID = Member.scan(name)[0]
#check if the book is available
Status = books[BookID]['Available']
#if the book is available check then check the different reservations
if Status == "Yes":
#if the book is not reserves then issue the book and add a new entry
if books[BookID]["Reserved"] == "No": #THIS IS LINE 31
dateToday = datetime.datetime.now().strftime('%Y-%m-%d')
loans[len(loans)+1]={'BookID':BookID, 'MemberID':MemberID, 'Date of loan': dateToday, 'Date of return':'NaN', 'Length of borrow':'NaN'}
books[BookID]["Available"] = "No"
print("You have now borrowed", title)
#if the books is reserved and the member is first in the queue
#remove the member from the reservation list and record new record
elif books[BookID]["Reserved"] == "Yes" and books[BookID]["ReservedID"][0] == MemberID:
dateToday = datetime.datetime.now().strftime('%Y-%m-%d')
loans[len(loans)+1] = {'BookID':BookID, 'MemberID':MemberID, 'Date of loan': dateToday, 'Date of return':'NaN', 'Length of borrow':'NaN'}
books[BookID]["Available"] = "No"
Loan.RemoveReservation(name, title)
if len(books[BookID]["ReservedID"]) == 0:
books[BookID]["Reserved"] = "No"
print("You have now borrowed", title)
#if the member has reserved the book but there is someone else renting it
elif books[BookID]["Reserved"] == "Yes" and MemberID in books[BookID]["ReservedID"]:
print(title, "is not available at the moment. You can reserve this though")
#if the book isnt available and the member hasnt reserved it
else:
print(title, "is not available")
#
#
elif Status == "No":
if MemberID in books[BookID]["ReservedID"]:
print(title, "not ready")
else:
print(title, "not ready")
Loan.Borrow(name="Charlie Roberts", title ="God Created the Integers")
print(books[Book.scan("God Created the Integer")[0]])
print(loans[len(loans)])

Answer 1

A KeyError means that that key does not exist in the dictionary. If you want to check for existence of a key, either wrap it in a try/catch:
try:
doSomething(myDict['invalidKey'])
except KeyError:
#Process error
OR
Check if the key exists first:
d = {"a": 1, "b": 2}
if "a" in d.keys():
#The key was in the dictionary
else:
#The key wasn't in the dictionary
If you want to add the key to your dictionary, you'll have to set the key equal to a value first:
>>> d = {}
>>> d['a']
KeyError
>>> d['a'] = "foo"
>>> d['a']
foo