无法接受用户输入并正确使用它

Question

好的，我已经处理了几天，但我自己无法修复它。

Python 3 并处理下面的这段代码。我的问题是变量类型和用户输入。此代码是更大代码的一部分，我希望用户（主要是我）能够使用有意义的变量名称（“m_earth”代表地球质量，以及类似的数量）作为“F1”计算的输入"，对于我想使用的其他人......如果......我可以先让这部分工作。

我尝试过使用“float”和“int”，但它确实会产生其他我无法修复的错误。

下面包含的代码是使用此代码时发生的情况。

有人有什么建议吗...请问？

谢谢

G = float(6.674E-11)

# All masses are in Kg
m_earth = 5.972E24
m_moon = 7.345E22

m1 = input('Enter the first mass  ')
print(m1, 'Kg')

m2 = input('Enter the second mass  ')
print(m2, 'Kg')

r = input('Enter the center-to-center distance from mass m1 to mass m2  ')

F1 = G * m1 * m2 / r ** 2
print('The gravitational force is  ', F1, "N")

Enter the first mass  m_earth
m_earth Kg
Enter the second mass  m_moon
m_moon Kg
Enter the center-to-center distance from mass m1 to mass m2  3E12
Traceback (most recent call last):
  File "C:/Users/xyz/PycharmProjects/My Python Programs/try it.py", line 15, in <module>
    F1 = G * m_earth * m_moon / r ** 2
TypeError: unsupported operand type(s) for ** or pow(): 'str' and 'int'

进程已完成，退出代码为 1

Answer 1

您收到此错误是因为 input() 总是 returns 一个字符串。您不能向 ints 或 floats 添加任意字符串的原因是因为在大多数情况下它没有意义。

考虑 3 + 'Hello'。您希望结果如何？

那么我们该如何处理呢？我们将其转换为 python 理解为允许执行算术函数的东西。在 python 中，这些类型是 int（整数）和 float 小数。为了论证，还有很多其他的，但您的示例不需要它们。

由于我们无法保证用户输入了号码，因此我们需要进行某种类型的检查以确保他们输入了号码。

那是我们可以使用 try/except 块的地方。

G = float(6.674E-11)

# All masses are in Kg
m_earth = 5.972E24
m_moon = 7.345E22

m1 = input('Enter the first mass  ')
print(m1, 'Kg')

m2 = input('Enter the second mass  ')
print(m2, 'Kg')

r = input('Enter the center-to-center distance from mass m1 to mass m2  ')

# any Error that occurs in the try block
# will hand control to the except block
# if the type of Exception in except is 
# the type of error that occurred
try:
    # here we try to convert the variable m1 of type str
    # to a variable of type float
    # since float() "returns" a float and does not convert in place
    # we need to catch the output it gives into the same variable
    m1 = float(m1)
    m2 = float(m2)
    r = float(r)
    F1 = G * m1 * m2 / r ** 2
    print('The gravitational force is  ', F1, "N")
# any conversion error here will result in a ValueError
# We can catch that specific error and alert the user they 
# mis-entered some data
except ValueError as v:
    print('Some of your input is not valid.')

但是您希望能够指定变量的名称。为此，您可以使用 python dict。 dict 将键映射到某个值。键可以是多种类型，但最重要的是，它们可以是 str，即 input() returns 的类型。在这种情况下，它可能是 m_earth.

# we need sys to do an early exit in the program
# if the data entered is not a key in the dict
import sys

G = float(6.674E-11)

# All masses are in Kg
my_dict = {'m_earth': 5.972E24,
           'm_moon': 7.345E22}

m1 = input('Enter the first mass  ')
# this will raise a KeyError
# if the key is not in your dict
try:
    m1 = my_dict[m1]
except KeyError as k:
    sys.exit('That name is invalid.')
print(m1, 'Kg')

m2 = input('Enter the second mass  ')
try:
    m2 = my_dict[m2]
except KeyError as k:
    sys.exit('That name is invalid.')

r = input('Enter the center-to-center distance from mass m1 to mass m2  ')

try:
    r = float(r)
    F1 = G * m1 * m2 / r ** 2
    print('The gravitational force is  ', F1, "N")
except ValueError as v:
    print('Some of your input is not valid.')

无法接受用户输入并正确使用它

Unable to accept user-input and use it without errors

variables

user-input

type-conversion

python-3.x