Проверьте, существует ли столбец в DataFrame
if 'A' in df.columns:
Ashamed Alligator
if 'A' in df.columns:if 'A' in df:import pandas as pd
numbers = {'set_of_numbers': [1,2,3,4,5,6,7,8,9,10]}
df = pd.DataFrame(numbers,columns=['set_of_numbers'])
df['equal_or_lower_than_4?'] = df['set_of_numbers'].apply(lambda x: 'True' if x <= 4 else 'False')
print (df)