import pandas as pd
df = pd.DataFrame({'A': [1, None, 'hello', True, 'world', 'mystr', 34.11]})
df['stringy'] = [isinstance(x, str) for x in df.A]
# A stringy
# 0 1 False
# 1 None False
# 2 hello True
# 3 True False
# 4 world True
# 5 mystr True
# 6 34.11 False