python-3.x - 如何将输入字符限制为字母

Question

我对python不太了解，我现在正在研究逆向工程，对于一个训练程序crackme.exe我在python上找到了这段代码。请告诉我如何检查输入的数字字符 - 只需要字母，并且必须排除数字或输出“输入错误”

def keygen(name):   
    word = 0          
    for letter in name:   
        word += ord(letter)
    
    return word ^ 0x5678 ^ 0x1234 
    

import sys   

if __name__ == '__main__':   
    if len(sys.argv) < 2:   
        print("Name")
        sys.exit(1)
    else:
        print(keygen(sys.argv[1].upper()))  


sys.argv
sys.exit(1)

标签： python-3.xreverse-engineering

Answer 1

您可以遍历输入字符串的每个字符并检查是否是字母表中的字母。

我在下面创建了一个函数，is_valid它应该可以解决您的问题。如果要更改哪些字符有效，可以通过编辑alphabet变量来实现。

alphabet = "abcdefghijklmnopqrstuvwxyz"

def is_valid(text):
    for char in text:
        # char.lower() makes sure the text is lowercase, otherwise "Hello" would not be valid because capital H wasn't in the alphabet.
        if char.lower() not in alphabet:
            return False
    else: # We've finished iterating, which means all characters were in the alphabet.
        return True

if __name__ == '__main__':   
    if len(sys.argv) < 2:   
        print("Name")
        sys.exit(1)
    else:
        if is_valid(sys.argv[1]): # Yay! Its valid so we can run our function
            print(keygen(sys.argv[1].upper()))
        else:
            sys.exit(1) # Its not valid so we should exit with Code 1