练习函数式编程的map和reduce

Author: SergioJune

test8.py

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+# 练习函数式编程的map和reduce
+from functools import reduce
+
+
+l = [x for x in range(-10, 10, 2)]
+print(l)
+l = list(map(abs, l))
+print(l)
+
+
+# reduce是将列表做累计运算
+# lambda是匿名函数
+num = reduce(lambda x, y: x + y, l)
+print(num)
+
+
+# 将一个字符串转换成整型
+def str2int(s):
+    def char2int(ch):
+        c = {str(x): x for x in range(10)}
+        return c[ch]
+
+    def fun(n1, n2):
+        return n1*10 + n2
+
+    return reduce(fun, map(char2int, s))
+
+
+num = str2int('12345')
+print(type(num), num)
+
+
+# 这是使用匿名函数的简便版
+def str2int2(s):
+    ch = {str(x): x for x in range(10)}
+    return reduce(lambda x, y: x*10+y, map(lambda x: ch[x], s))
+
+
+num = str2int2('12345')
+print(type(num), num)
+
+
+# 作业：利用map()函数，把用户输入的不规范的英文名字，变为首字母大写，其他小写的规范名字
+def normalize(name):
+    # capitalize()函数是将字符串的首字母大写
+    return list(map(lambda x: x.capitalize(), name))
+
+
+L = ['adam', 'LISA', 'barT']
+print(normalize(L))
+
+
+# 作业2：Python提供的sum()函数可以接受一个list并求和，请编写一个prod()函数，可以接受一个list并利用reduce()求积
+def prod(x, y):
+    return x*y
+
+
+num = reduce(prod, [3, 5, 7, 9])
+print(num)
+
+
+# 作业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
+def str2float(s):
+    ch = {str(x): x for x in range(10)}
+    # 先将字符串分割
+    L = s.split('.')
+    # 整数部分
+    n1 = reduce(lambda x, y: x*10 + y, map(lambda x: ch[x], L[0]))
+    # 小数部分
+    n2 = reduce(lambda x, y: x * 10 + y, map(lambda x: ch[x], L[1]))
+    n2 *= 0.1**len(L[1])
+    return n1+n2
+
+
+num = str2float('123.456')
+print(num)