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如何匹配从输入到列表的元素?

原标题：How to match elements from input to list?

I m new to python, and I just wanted to ask how you would match one element from a user input to a list. I m currently working on a caesar cipher program, and I basically typed up a list of the alphabets: alphabet = [ a , b , c , d ,...] Then asked the user for a word to encrypt, text = input( Enter your message ) and the shift amount, I figured I could set an empty string variable and then loop through (for loop) each letter to shift it. But this is where I got stuck, how will I shift each letter in the input by the shift amount using the list? I tried to loop through the input using the indexes of the list alphabet, but since had no idea what I was doing it didn t work.

问题回答

Here s a generic implementation of the caesar-cipher, that should work for any shift amount, and any charset. Feel free to get rid of the type hinting if you feel it hinders readability. I personally would prefer to have it though. import string from typing import Hashable, Iterable, Sequence, TypeVar T = Hashable def caesar_ciper(message: Iterable[T], k: int, charset: Sequence[T] = string.ascii_lowercase) -> Iterable[T]: n = len(charset) char_idx = dict(zip(charset, range(n))) shift = lambda x: charset[(char_idx[x] + k) % n] return map(shift, message) message = abcxyz # read from user k = 3 # read from user encoded = .join(caesar_ciper(message, k)) assert encoded == defabc

So if you are just trying to shift by a constant amount, then this is fairly straightforward, you could have done with this a string rather than a list as well. The main thing to think about is the wrapping, which we can do with modulus operator. Lets say you want to shift 3 places: So if the index + shift is less than 26, the modulo operation doesn t change anything 2 + 3 % 26 = 5 If index + shift is 26 or greater, the modulo operation wraps it around. 24 + 3 % 26 = 1 example = "zebra" alphabet = [ a , b , c , d , e , f , g , h , i , j , k , l , m , n , o , p , q , r , s , t , u , v , w , x , y , z ] encrypted = for char in example: if char in alphabet: i = alphabet.index(char) j = (i + 3) % 26 encrypted += alphabet[j] else: encrypted += char

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