Python being Javascript

gistfile1.txt

Python 3.9.7 (default, Sep 16 2021, 13:09:58) 
[GCC 7.5.0] :: Anaconda, Inc. on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import pandas as pd
>>> df_1 = pd.DataFrame(columns=['a', 'b'])
>>> df_2 = pd.DataFrame([{'a':42, 'b':43}, {'a':47, 'b':48}])
>>> def foo(row, to_add):
...   print('hi')
...   row['a'] = row['a'] + to_add
...   print('bye')
...   return row
... 
>>> df_2.apply(lambda row: foo(row, 2), axis=1)
hi
bye
hi
bye
    a   b
0  44  43
1  49  48
>>> df_1.apply(lambda row: foo(row, 2), axis=1)
hi
Empty DataFrame
Columns: [a, b]
Index: []