Using conditional if/else logic with pandas dataframe columns

My dataframe called pw2 looks something like this, where I have two columns, pw1 and pw2, which are probability of wins. I'd like to perform some conditional logic to create another column called WINNER based off pw1 and pw2.

+-------------------------+-------------+-----------+-------------+
|          Name1          |     pw1     |   Name2   |     pw2     |
+-------------------------+-------------+-----------+-------------+
| Seaking                 | 0.517184213 | Lickitung | 0.189236181 |
| Ferrothorn              | 0.172510623 | Quagsire  | 0.260884258 |
| Thundurus Therian Forme | 0.772536272 | Hitmonlee | 0.694069408 |
| Flaaffy                 | 0.28681284  | NaN       | NaN         |
+-------------------------+-------------+-----------+-------------+

I want to do this conditionally in a function but I'm having some trouble.

• if pw1 > pw2, populate with Name1
• if pw2 > pw1, populate with Name2
• if pw1 is populated but pw2 isn't, populate with Name1
• if pw2 is populated but pw1 isn't, populate with Name2

But my function isn't working - for some reason checking if a value is null isn't working.

def final_winner(df):
    # If PW1 is missing and PW2 is populated, Pokemon 1 wins
    if df['pw1'] = None and df['pw2'] != None:
        return df['Number1']
    # If it's the same thing but the other way around, Pokemon 2 wins
    elif df['pw2'] = None and df['pw1'] != None:
        return df['Number2']
    # If pw2 is greater than pw1, then Pokemon 2 wins
    elif df['pw2'] > df['pw1']:
        return df['Number2']
    else
        return df['Number1']

pw2['Winner'] = pw2.apply(final_winner, axis=1)