Pandas: How can I update dataframe values? I have two spreadsheets where one is updating the other.

How can I update this data using the pandas library?

Example, where 'b' updates 'a':

a = {'field': ['a', 'b', 'c'], 'value': ["", None, 1]}
b = {'field': ['a', 'b', 'd'], 'value': [1, 2, 1]}


Expected outcome:

c = {'field': ['a', 'b', 'c', 'd'], 'value': [1, 2, 1, 1]}
df_a = pandas.DataFrame(a)

df_b = pandas.DataFrame(b)

c = pandas.concat([df_a, df_b], ignore_index=True).drop_duplicates(subset=['field'], keep='last')