为何Python温度转换函数传入列表时出现“can't multiply sequence by non-int of type 'float'”错误？

问题描述 #

作为Python新手，编写了摄氏度（C）、华氏度（F）、开尔文（K）互转的函数，单个数值输入时正常，但传入列表[0,10,20]时触发错误：TypeError: can't multiply sequence by non-int of type 'float'，尝试声明x的数值类型后仍未解决。

原代码 #

import warnings

def convTemp(x=0, fro="C", to="F"):
    if fro == "C" and to == "F":
        x = 1.8 * x + 32
        return x
    elif fro == "C" and to == "K":
        x = x + 273.15
        return x
    elif fro == "F" and to == "C":
        x = x * (5/9)-32
        return temp
    elif fro == "F" and to == "K":
        x = (x * (5/9)-32)+273.15
        return x
    elif fro == "K" and to == "C":
        x = x - 273.15
        return x
    elif fro == "K" and to == "F":
        x = (9/5)*(x - 273.15) + 32
        return x
    else:
        if fro == to:
            warnings.warn("Your 'fro' parameter is the same as your 'to' parameter!")

报错栈 #

TypeError                                 Traceback (most recent call last)
<ipython-input-2-e9e7ea7efd49> in <module>
      1 assert convTemp(0) == 32
----> 2 assert convTemp([0,10,20]) == [32, 50, 68]
      3 
<ipython-input-1-a8e50b49bfb6> in convTemp(x, fro, to)
      2 def convTemp(x=0, fro="C", to="F"):
      3     if fro == "C" and to == "F":
----> 4         x = 1.8 * x + 32
      5         return x
      6     elif fro == "C" and to == "K":

TypeError: can't multiply sequence by non-int of type 'float'

错误原因 #

Python中列表不能直接与浮点数相乘：整数乘列表会重复元素（如2 * [1,2]得到[1,2,1,2]），但浮点数与列表的乘法操作不被支持，因此传入列表时触发报错。此外原代码还存在两个逻辑错误：

• 华氏度转摄氏度的公式错误，正确逻辑应为(x - 32) * 5/9，原代码写成了x * 5/9 -32
• 华氏度转摄氏度分支中错误返回了未定义的变量temp，应为返回x

解决方案 #

修改函数，使其同时支持单个数值和列表（或其他可迭代对象）输入，同时修复公式错误：

import warnings
from collections.abc import Iterable

def convTemp(x=0, fro="C", to="F"):
    # 单个数值的转换逻辑
    def convert_single(val):
        if fro == "C" and to == "F":
            return 1.8 * val + 32
        elif fro == "C" and to == "K":
            return val + 273.15
        elif fro == "F" and to == "C":
            return (val - 32) * (5/9)  # 修复公式顺序
        elif fro == "F" and to == "K":
            return (val - 32) * (5/9) + 273.15  # 修复公式顺序
        elif fro == "K" and to == "C":
            return val - 273.15
        elif fro == "K" and to == "F":
            return (9/5)*(val - 273.15) + 32
        else:
            if fro == to:
                warnings.warn("Your 'fro' parameter is the same as your 'to' parameter!")
            return val  # 单位相同时返回原值
    
    # 判断输入是否为可迭代对象（排除字符串）
    if isinstance(x, Iterable) and not isinstance(x, (str, bytes)):
        return [convert_single(val) for val in x]
    # 单个数值输入的情况
    else:
        return convert_single(x)

测试验证 #

执行以下断言代码可验证功能正常：

assert convTemp(0) == 32.0
assert convTemp([0,10,20]) == [32.0, 50.0, 68.0]
assert convTemp(32, fro="F", to="C") == 0.0
assert convTemp([32, 50, 68], fro="F", to="C") == [0.0, 10.0, 20.0]

内容的提问来源于stack exchange，提问作者LeroyBrown