text: 
  from .network import Network
  from .legacy_networks import NETWORKS
  
  from pycoin.tx.Tx import Tx as BitcoinTx
  from pycoin.block import Block as BitcoinBlock
  
  from ..serialize import h2b
  
  BUILT_IN_NETWORKS = [
  
      # BTC bitcoin mainnet : xprv/xpub
      Network(
          'BTC', "Bitcoin", "mainnet",
          b'\x80', b'\0', b'\5', h2b("0488ADE4"), h2b("0488B21E"),
          b'\6', b'\x0a',
          BitcoinTx, BitcoinBlock,
          h2b('F9BEB4D9'), 8333, [
              "seed.bitcoin.sipa.be", "dnsseed.bitcoin.dashjr.org",
              "bitseed.xf2.org", "dnsseed.bluematt.me",
          ]
      ),
  
      # BTC bitcoin testnet : tprv/tpub
      Network(
          "XTN", "Bitcoin", "testnet3",
          b'\xef', b'\x6f', b'\xc4', h2b("04358394"), h2b("043587CF"),
          b'\3', b'\x28',
          BitcoinTx, BitcoinBlock,
          h2b('0B110907'), 18333, [
              "bitcoin.petertodd.org", "testnet-seed.bitcoin.petertodd.org",
              "bluematt.me", "testnet-seed.bluematt.me"
          ]
      )
  ]
  
  
  def _transform_NetworkValues_to_Network(nv):
      defaults = dict(
          tx=None, block=None, magic_header=None, dns_bootstrap=[], default_port=None,
          address_wit=None, pay_to_script_wit=None)
      defaults.update(nv._asdict())
      return Network(**defaults)
  
  
  def _import_legacy():
      for n in NETWORKS:
          n1 = _transform_NetworkValues_to_Network(n)
          BUILT_IN_NETWORKS.append(n1)
  
  
  _import_legacy()
  