输入:"-78.506"
输出:-78.506
代码:
def str2float(num):
f1 = 1
f2 = 0
y = 1
u = 0
for i in range(len(a)):
if num[i]=='-':
f1 = -1 # 用来判断正数还是负数
elif num[i]=='.':
f2 = 1 # 用来判断处于整数部分还是小数部分
elif not f2:
u = u*10 + int(num[i])
else:
y = 10*y
u += int(num[i])/y
return u*f1