python学习日记（3）

map函数

def f(x):
    return x*x

r = map(f, [1, 2, 3, 4, 5])
list(r)

reduce函数

from functools import reduce

reduce(f, [x1, x2, x3, x4]) = f(f(f(x1, x2), x3), x4)

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组合使用

from functools import reduce

def str2int(s):
    def fn(x, y):
        return x * 10 + y
    def char2num(s):
        return {'0': 0, '1': 1, '2': 2, '3': 3, '4': 4, '5': 5, '6': 6, '7': 7, '8': 8, '9': 9}[s]
    return reduce(fn, map(char2num, s))

测试

测试1

利用map函数，将输入的不规范的英文名字输出为规范的英文名字

def normalize(name):
    return name.capitalize()

if __name__ == "main":
    L1 = ['sdhi', 'HFIS', 'bsiH']
    L2 = list(map(normalize, L1))
    print(L2)

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测试2

求累积

from functools import reduce
def prod(L):
    return reduce(lambda x, y : x * y, L)

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测试3

利用map和reduce编写一个str2float函数，把字符串’123.456’转换成浮点数123.456：

from functools import reduce
def str2float(s):
    def change(ss):
        return {'0': 0, '1': 1, '2': 2, '3': 3, '4': 4, '5': 5, '6': 6, '7': 7, '8': 8, '9': 9, '.' : None}[ss]
    ins = 0
    for str in s:
        ins += 1
        if(str == '.'):
            break
    return reduce(lambda x, y: x * 10 + y, [re for re in list(map(change, s)) if re != None]) / (10 ** (len(s) -ins ))