Python化学物种验证代码输入始终无效问题排查请求

问题描述 #

编写的Python代码用于验证用户输入是否为有效化学物种，但无论输入列表中的正确名称或分子式，都会返回无效提示。原代码如下：

import numpy as np

chemlist = np.array(["carbon dioxide", "co2",
                     "carbon monoxide", "co",
                     "ethane", "c2h6",
                     "methane", "ch4",
                     "nitrogen", "n2",
                     "oxygen", "o2",
                     "water", "h2o (liquid)",
                     "water vapour", "h2o (gas)"])

print(chemlist)
chemical = input("Enter name or the chemical formula of your compound:\n")
chemical = chemical.lower()
print(chemical)

for i in range(len(chemlist)):
    if chemical == chemlist[i]:
        break
    else:
        print("Invalid chemical name. Please input one from the list below:\n")
        print(chemlist)
        chemical = input("Enter name or the chemical formula of your compound again:\n")

temperature = 0
temperature = float(input("Enter your temperature in degrees Kelvin:\n"))

if temperature <= 273.15 or temperature >= 673.15:
    temperature = float(input('Temperature is not in range. Enter your temperature in degrees Kelvin again:\n'))
else:
    break

问题分析 #

1. 循环逻辑错误：原for循环会逐个对比列表元素，只要当前元素不匹配就立刻触发错误提示并重新输入，完全没机会检查后续元素。比如输入co2，第一次对比的是carbon dioxide，不匹配就直接进入else分支，根本不会去对比下一个元素co2。
2. 温度验证逻辑缺陷：温度输入只做了一次重新输入判断，若用户再次输入无效值，代码不会继续校验；另外else分支的break语句没有对应的循环，会直接导致语法错误。

修正后的代码 #

import numpy as np

chemlist = np.array(["carbon dioxide", "co2",
                     "carbon monoxide", "co",
                     "ethane", "c2h6",
                     "methane", "ch4",
                     "nitrogen", "n2",
                     "oxygen", "o2",
                     "water", "h2o (liquid)",
                     "water vapour", "h2o (gas)"])

print("Available chemicals:", chemlist)

# 验证化学物种的循环：直到输入有效为止
while True:
    chemical = input("\nEnter name or the chemical formula of your compound:\n").lower()
    if chemical in chemlist:
        print(f"Valid chemical: {chemical}")
        break
    else:
        print("Invalid chemical name. Please input one from the list below:")
        print(chemlist)

# 验证温度的循环：直到输入有效为止
while True:
    try:
        temperature = float(input("\nEnter your temperature in degrees Kelvin:\n"))
        if 273.15 < temperature < 673.15:
            print(f"Valid temperature: {temperature} K")
            break
        else:
            print("Temperature is not in range (273.15 K < T < 673.15 K). Try again.")
    except ValueError:
        print("Please enter a valid number for temperature.")

修改说明 #

• 把化学物种验证改成while True循环，用in关键字直接判断输入是否在列表中，逻辑更简洁，直到输入有效才退出循环。
• 温度验证也改成循环，同时加入异常处理，防止用户输入非数字导致报错，确保只有输入有效范围内的数值才会退出。
• 移除了无意义的break语句，修复了语法错误。

内容的提问来源于stack exchange，提问作者Fatimah Humaira Khalid