将用户输入限制在 Python 中的某个范围内 [英] Limiting user input to a range in Python

问题描述

在下面的代码中，您会看到它要求一个移位"值.我的问题是我想将输入限制为 1 到 26.

In the code below you'll see it asking for a 'shift' value. My problem is that I want to limit the input to 1 through 26.

    For char in sentence:
            if char in validLetters or char in space: #checks for
                newString += char                     #useable characters
        shift = input("Please enter your shift (1 - 26) : ")#choose a shift
        resulta = []
        for ch in newString:
            x = ord(ch)      #determines placement in ASCII code
            x = x+shift      #applies the shift from the Cipher
            resulta.append(chr(x if 97 <= x <= 122 else 96+x%122) if ch != \
            ' ' else ch) # This line finds the character by its ASCII code

如何轻松做到这一点?

推荐答案

使用 while 循环不断询问他们的输入，直到您收到您认为有效的内容:

Use a while loop to keep asking them for input until you receive something you consider valid:

shift = 0
while 1 > shift or 26 < shift:
    try:
        # Swap raw_input for input in Python 3.x
        shift = int(raw_input("Please enter your shift (1 - 26) : "))
    except ValueError:
        # Remember, print is a function in 3.x
        print "That wasn't an integer :("

您还需要在 int() 调用周围有一个 try-except 块，以防您收到 ValueError (例如，如果他们输入 a).

You'll also want to have a try-except block around the int() call, in case you get a ValueError (if they type a for example).

请注意，如果您使用 Python 2.x，您需要使用 raw_input() 而不是 input().后者将尝试将输入解释为 Python 代码 - 这可能非常糟糕.

Note if you use Python 2.x, you'll want to use raw_input() instead of input(). The latter will attempt to interpret the input as Python code - that can potentially be very bad.

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