后一个分数的分子=前一个分数的分子+分母，后一个分数的分母=前一个分数的分子，循环个20次就有结果。注意，假设分子为a，分母为b，虽然 a = a + b，
但此时a已经变成 a+b 了，所以再给b重新赋值的时候，得是 (a+b)-b 才能等于原分母b，所以重新赋值时就得写成 a-b
方法一
from fractions import Fraction
def fibonacci(n):
a, b = 1, 2
res = [1]
i = 1
while i < n:
a, b = b, a+b
res.append(a)
i += 1
else:
return res
result = fibonacci(21)
sum_result = sum([Fraction(i[0],i[1]) for i in zip(result[1:],result[0:-1])])
print (sum_result)
方法二
from
fractions
import
Fraction
sum
=
0
a, b
=
2
,
1
for
i
in
range
(
20
):
sum
=
sum
+
Fraction(a
/
b)
a
=
a
+
b
b
=
a
-
b
print
(
sum
)
方法三
sum
=
0
a, b
=
2
,
1
for
i
in
range
(
20
):
sum
=
sum
+
a
/
b
a
=
a
+
b
b
=
a
-
b
print
(
sum
)