input: Write a function to check if the first string is a subsequence of the second string. If the first string is a subsequence, the function should return True; otherwise, it should return False.
  def is_subsequence(str1, str2):
      i = 0
      j = 0
  
      while(i < len(str1) and j < len(str2)):
          if str1[i] == str2[j]:
              i += 1
          j += 1
  
      return i == len(str1)
  
  assert is_subsequence('abc', 'qaxbcy')==True
  assert is_subsequence('aec', 'qasdbcyde')==False
  assert is_subsequence('abc', 'ahbgdc')==True
  assert is_subsequence('axc', 'ahbgdc')==False
  assert is_subsequence('xyz', 'xzyxzy')==True
output: def is_subsequence(str1, str2):
      i = 0
      j = 0
  
      while(i < len(str1) and j < len(str2)):
          if str1[i] == str2[j]:
              i += 1
          j += 1
  
      return i == len(str1)