rarest lenght

squares = [x*x for x in range(10)]

from collections import Counter

def length(number):
  return len(str(number))

def rarest_length(numbers):
  length_counts = Counter(length(n) for n in numbers)
  rarest_length_count = min(length_counts.values())
  return min(length for (length, count) in length_counts.items() if count == rarest_length_count)

print(rarest_length(squares))