PYTHON：处理 KeyError

Question

I was trying to solve a problem (checking if string s and t are anagram) in Python:

Algorithm: To examine if t is a rearrangement of s , we can count occurrences of each letter in the two strings and compare them. Since both s and t contain only letters from az , a simple counter table of size 26 is sufficient.

We could increment the counter for each letter in s and decrement the counter for each letter in t , then check if the counter reaches back to zero.

Code:

class Solution:
    def isAnagram(self, s: str, t: str) -> bool:
        
        if len(s) != len(t): 
            return False
        
        table = {} 
        
        for i in range(len(s)):
            table[s[i]] = table.get(table[s[i]], 0) + 1
            
        for i in range(len(t)):
            table[t[i]] = table.get(table[s[i]], 0) - 1
            if table[t[i]] < 0:
                return False
            
        return True

Yet, I get a KeyError in the first loop. To handle that, I tried using .get() but still cannot tackle.

I am getting the following error:

Answer 1

• While looking for value in dict , you lookup twice: table.get(table[s[i]], 0) .
• [] and .get() are synonymous except that latter is safe when empty and returns default.
• This should be the loop you'd need. Credits to @deadshot.

        for i in range(len(s)):
            table[s[i]] = table.get(s[i], 0) + 1
            
        for i in range(len(t)):
            table[t[i]] = table.get(t[i], 0) - 1
            if table[t[i]] < 0:
                return False