docs: def calculate_tx_fee(tx_size: int) -> Decimal:
      '''return tx fee from tx size in bytes'''
  
      per_kb_cost = 0.01
      min_fee = Decimal(0.001)
  
      fee = Decimal((tx_size / 1000) * per_kb_cost)
  
      if fee <= min_fee:
          return min_fee
      else:
          return fee