The window is fixed in size so the solution should not be that complicated

import math
from collections import Counter
class Solution:
  def findPermutation(self, text, pattern):
    # edge case
    if text == "":
      return False 

    pattern_frq = Counter(pattern)
    text_freq = {}

    # the initial window frequency count
    for i in range(len(pattern)):
      text_freq[text[i]] = text_freq.get(text[i], 0)
      text_freq[text[i]] += 1
      
    # move the window and check the frequencies 
    j = 0
    i = len(pattern) - 1 
    while i < len(text):
      if text_freq == pattern_frq:
        return True
      
      # move i and add the i frequency to the map
      i += 1
      if i == len(text):
        break
      text_freq[text[i]] = text_freq.get(text[i], 0)
      text_freq[text[i]] += 1
      
      # delete the old j frequency from the map and move j
      text_freq[text[j]] -= 1
      if text_freq[text[j]] == 0:
        del text_freq[text[j]]
      j += 1
      
    return False