Математическая операция Pandas от строки

import pandas as pd
import numpy as np
df = pd.DataFrame(np.array([[1, 2], [4, 5], [7, 8]]), columns=['a', 'b'])
df.head()
#   a	b
# 0	1	2
# 1	4	5
# 2	7	8

df['c'] = eval( "df['a'] + df['b']" )
df.head()
#   a	b	c
# 0	1	2	3
# 1	4	5	9
# 2	7	8	15
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