杨辉三角和字符串转浮点数

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def triangles():
    L = [1]
    while 1:
        yield L
        L.append(0)
        L = [L[i-1] + L[i] for i in range(len(L))]
n = 0
for t in triangles():
     print(t)
     n = n + 1
     if n == 10:
        break

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[1]
[1, 1]
[1, 2, 1]
[1, 3, 3, 1]
[1, 4, 6, 4, 1]
[1, 5, 10, 10, 5, 1]
[1, 6, 15, 20, 15, 6, 1]
[1, 7, 21, 35, 35, 21, 7, 1]
[1, 8, 28, 56, 70, 56, 28, 8, 1]
[1, 9, 36, 84, 126, 126, 84, 36, 9, 1]

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from functools import reduce


def str2float(s):
    def s2n(s):
        return {'0': 0,
                '1': 1,
                '2': 2,
                '3': 3,
                '4': 4,
                '5': 5,
                '6': 6,
                '7': 7,
                '8': 8,
                '9': 9,
                '.': -1}[s]

    nums = list(map(s2n, s))
    if -1 in nums:
        dot_index = nums.index(-1)
        nums.remove(-1)
    else:
        dot_index = len(nums)
    return reduce(lambda x, y: x + y, map(lambda x: x * 10 ** (dot_index - nums.index(x) - 1), nums)

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print(str2float('0'))
print(str2float('123.456'))
print(str2float('123.45600'))
print(str2float('0.1234'))
print(str2float('.1234'))
print(str2float('120.0034'))

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0
123.456
123.456
0.12340000000000001  # 囧
0.12340000000000001
120.0034