impute dates with apply and lambdas with change log

impute_lambdas_changelog.py

# store the lambda function as an object
impute = lambda x: x[col1].replace(year=x[col2].year) if x[col1].year > curr_year \
                   else x[col1].replace(year=x[col2].year) if x[col1].year < past_year \
                   else x[col1]

# simplify the code later by calling impute
df[col_new] = df.apply(impute, axis=1)

# a new dataframe called change_log
change_log = df[(df[col1].dt.year > curr_year)]

# write to csv
change_log.to_csv('change_log.csv')

# replace col1 with new_col values
df[col1] = df[col_new]

# drop the temporary new_col
df.drop(columns=col_new, inplace=True)