pandas combine two columns with null values

Use fillna on one column with the fill values being the other column:

df['foodstuff'].fillna(df['type'])

The resulting output:

0      apple-martini
1          apple-pie
2    strawberry-tart
3            dessert
4               None

• fillna both columns together
• sum(1) to add them
• replace('', np.nan)

---

df.fillna('').sum(1).replace('', np.nan)

0      apple-martini
1          apple-pie
2    strawberry-tart
3            dessert
4                NaN
dtype: object

you can use the combine method with a lambda:

df['foodstuff'].combine(df['type'], lambda a, b: ((a or "") + (b or "")) or None, None)

(a or "") returns "" if a is None then the same logic is applied on the concatenation (where the result would be None if the concatenation is an empty string).