[Python] concatenate two data frame, and deal with NaN

import pandas as pd 

ng_list1 = [{"name": "Jake", "grade": 80}, {"name": "Annie", "grade": 90}, {"name": "Jane"}] 
ng_list2 = [{"name": "Sam", "grade": 74}, {"name": "Ben", "grade": 64}, {"name": "Sky", "grade": 77}, {"name": "Annie", "grade": 90}] 
 
# create data frame 
df1 = pd.DataFrame(ng_list1)
df2 = pd.DataFrame(ng_list2)
print(df1, "\n")
print(df2, "\n")

# concatenate df1 and df2
df = pd.concat([df1, df2], ignore_index=True)
print(df, "\n") 

# remove duplicates
df.drop_duplicates(inplace=True, ignore_index=True) 

# dealing with NaN
# if you wanna drop any row including NaN, use df.dropna(inplace=True)
# if you wanna drop a row with NaN for all columns, use df.dropna(how="all", inplace=True)
# if you wanna fill all NaN with 0, use df.fillna(0, inplace=True)
df.fillna(0, inplace=True)
print(df, "\n")