Minimum window substring

class Solution:
    def minWindow(self, s: str, t: str) -> str:
        from collections import defaultdict
        schars = defaultdict(int)
        tchars = defaultdict(int)

        if len(t) > len(s):
            return ""

        for i in t:
            tchars[i] += 1

        currentMatch, requiredMatch = 0, len(tchars)

        left = 0

        currentAns = [-1, -1]
        currentAnsLen = float('inf')

        for right in range(len(s)):
            if s[right] in tchars:
                schars[s[right]] += 1
                if schars[s[right]] == tchars[s[right]]:
                    currentMatch += 1
            while currentMatch == requiredMatch:
                newAnsLen = right - left + 1
                if newAnsLen < currentAnsLen:
                    currentAns = [left, right]
                    currentAnsLen = newAnsLen

                if s[left] in tchars:
                    schars[s[left]] -= 1
                    if schars[s[left]] == tchars[s[left]]-1:
                        currentMatch -= 1
                left += 1


        if currentAnsLen != float('inf'):
            return s[currentAns[0]: currentAns[1]+1]
        return ""