Creating an IF statement in Python that looks at previous IF statement output

Question

I am having difficulty creating an IF statement that does the following:

• If C1 = Buy, then Buy
• If C2 = Sell, then Sell
• If C1 & C2 = nan,

Answer 1

Instead of doing the previous if statement, you can simply look at what has been previously put into the c3 list (as that is a result of the previous if statement).

Here is an example of how you can achieve this in python:

c1 = ["Buy", "nan", "nan", "nan", "Buy", "nan", "nan", "nan", "nan", "Buy", "nan"]
c2 = ["nan", "nan", "Sell", "nan", "nan", "Sell", "Sell", "nan", "nan", "nan", "Sell"]

c3 = []
for index in range(len(c1)):
    if c1[index] == "Buy":
        c3.append("Buy")
    elif c2[index] == "Sell":
        c3.append("Sell")
    elif c1[index] == "nan" and c2[index] == "nan": # Implied if reached this point (so else would also suffice here)
        c3.append(c3[index-1]) # look at previous result in list
print(c3)

Output:

['Buy', 'Buy', 'Sell', 'Sell', 'Buy', 'Sell', 'Sell', 'Sell', 'Sell', 'Buy', 'Sell']