[Python] Multiply the value determined for each section

I am in a situation where I need to multiply several columns by the value corresponding to the interval.

I'm using Pandas, but I'm using a for loop to get the value as follows.

I think there is a better way than this, can someone give me some advice?

sample:

import pandas as pd

d = {
5: 5,
4: 7,
3: 2,
2: -4,
1: -5,
}
def mul(value):
if value < 1: return value * 0.01
elif 5 < value: return value * 20
for k, v in d.items():
if value <= k:
val = value * v
break
return val

a = [
{'a': 5, 'b': 10, 'c': 2},
{'a': 4, 'b': 0.5, 'c': 4},
{'a': 3.5, 'b': 1.5, 'c': 5},
{'a': 2.1, 'b': 5, 'c': 6},
{'a': 0.1, 'b': 1, 'c': 7},
]

df = pd.DataFrame(a)
a = []
b = []
for i in df.values:
a.append(mul(i[0]))
b.append(mul(i[1]))
df['a1'] = a
df['b1'] = b
print(df.head())

"""
a b c a1 b1
0 5.0 10.0 2.0 25.000 200.000
1 4.0 0.5 4.0 20.000 0.005
2 3.5 1.5 5.0 17.500 7.500
3 2.1 5.0 6.0 10.500 25.000
4 0.1 1.0 7.0 0.001 5.000
"""

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