longest-substring-without-repeating-characters

Given a string, find the length of the longest substring without repeating characters.

Example 1:

Input: "abcabcbb"
Output: 3 
Explanation: The answer is "abc", with the length of 3. 
Example 2:

Input: "bbbbb"
Output: 1
Explanation: The answer is "b", with the length of 1.
Example 3:

Input: "pwwkew"
Output: 3
Explanation: The answer is "wke", with the length of 3. 
             Note that the answer must be a su
             
My code:
class Solution:
    def lengthOfLongestSubstring(self, s):
        """
        :type s: str
        :rtype: int
        """
        length=len(s)
        tmp_dict={}
        tmp_len=length
        start=0
        result=0
        i=0
        while i<length:
            if s[i] not in tmp_dict.keys():
                tmp_dict[s[i]]=1
                i=i+1
                if result<i-start:
                    result=i-start
                
            else:
                tmp_dict.pop(s[start])
                start+=1
                
                
        
        return result
        
Solution:
https://leetcode.com/problems/longest-substring-without-repeating-characters/