python函数式编程reduce

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#python函数式编程之reduce用法

reduce(f,序列)
reduce用f在序列上的相邻元素上作用，然后把结果继续和下一个元素迭代计算
reduce返回什么结果关键看f函数

  1. example 1: reduce计算和
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    from functools import reduce
    def add(x,y):
        return x+y
    ans = reduce(add,[1,2,3,4,5,6,7,8,9])
    print(ans)
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45
  1. example 2: reduce计算积的和
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    from functools import reduce
    def fn(x,y):
        return x*10+y
    ans =    reduce(fn,[1,2,3,4,5,6,7,8,9])
    print(ans)
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123456789
  1. example 3: reduce把字符串转为数字
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    def char2num(a):
        digit = {'0':0,'1':1,'2':2,'3':3,'4':4,'5':5,'6':6,'7':7,'8':8,'9':9}
        return digit[a]
    ans = reduce(fn,map(char2num,['1','2','3']))
    ans1 = reduce(fn,map(char2num,'123456'))
    print(ans,ans1,end=' ')
    print()
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123 123456
  1. example 4: 提炼为cha2num函数
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    digit = {'0':0,'1':1,'2':2,'3':3,'4':4,'5':5,'6':6,'7':7,'8':8,'9':9}
    def str2num(s):
        def fn(x,y):
            return x*10+y
        def char2num(a):
            return digit[a]
        return reduce(fn,map(char2num,s))
    s = '12345678'
    print(str2num(s))
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12345678
  1. example5: cha2num函数用lamda函数式简化
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    def str2num(s):
        return reduce(lambda x,y:x*10+y,map(lambda x:digit[x],s))
    print(str2num('321'))
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321
  1. test1：将字符串转为首字母大写，其余小写
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    def normalize(name):
        ans = name.lower().capitalize()
        return ans
    L1 = ['adam', 'LISA', 'barT']
    L2 = list(map(normalize,L1))
    print(L2)
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['Adam', 'Lisa', 'Bart']
  1. test2:求积
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    def prod(L):
        return reduce(lambda x,y:x*y,L)
    print('3*5*7*9 = ',prod([3,5,7,9]))
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3*5*7*9 = 945
  1. test3:字符串转为浮点数
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    digit = {'0':0,'1':1,'2':2,'3':3,'4':4,'5':5,'6':6,'7':7,'8':8,'9':9}
    def str2float(s):
        j = 0
        ans1 = 0.0
        ans2 = 0
        length = len(s)
        flag = False
        for i in (range(length)):
            if(s[i] == '.'):
                j = 0
                flag  = True
                continue
            if(flag):
                j = j + 1
                ans2 = ans2+digit[s[i]]*pow(0.1,j)
            else:
                ans1 = ans1*10+digit[s[i]]
        return ans1+ans2
    print(str2float('12.23'))
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12.23