old_contents: 
  class Interpreter(object):
  
      def __init__(self):
          self.initialize()
  
      def initialize(self):
          self.stack = []
          self.altstack = []
          self.pc = 0
          self.pbegincodehash = 0
          self.nop_count = 0
          self.vf_exec = []
          self.errstr = ''
          self.flags = 0
  
  
      """
      Verifies a Script by executing it and returns true if it is valid.
      This function needs to be provided with the scriptSig and the scriptPubkey
      separately.
  
      :param script_sig: the script's first part (corresponding to the tx input)
      :param script_pubkey: the script's last part (corresponding to the tx output)
      :param tx: the transaction containing the script_sig in one input (used to
          check signature validity for some opcodes like OP_CHECKSIG)
      :param nin: index of the transaction input containing the scriptSig verified.
      :param flags: evaluation flags. See Interpreter.SCRIPT_* constants
  
      Translated from bitcoind's VerifyScript
      """
      def verify(self, script_sig, script_pubkey, tx, nin, flags):
          pass
  
new_contents: from bitforge import Transaction
  from bitforge.tools import Buffer
  
  
  class Interpreter(object):
  
      def __init__(self):
          self.initialize()
  
      def initialize(self):
          self.stack = []
          self.altstack = []
          self.pc = 0
          self.pbegincodehash = 0
          self.nop_count = 0
          self.vf_exec = []
          self.errstr = ''
          self.flags = 0
  
  
      """
      Verifies a Script by executing it and returns true if it is valid.
      This function needs to be provided with the scriptSig and the scriptPubkey
      separately.
  
      :param script_sig: the script's first part (corresponding to the tx input)
      :param script_pubkey: the script's last part (corresponding to the tx output)
      :param tx: the transaction containing the script_sig in one input (used to
          check signature validity for some opcodes like OP_CHECKSIG)
      :param nin: index of the transaction input containing the scriptSig verified.
      :param flags: evaluation flags. See Interpreter.SCRIPT_* constants
  
      Translated from bitcoind's VerifyScript
      """
      def verify(self, script_sig, script_pubkey, tx, nin, flags):
          self.script = script_sig
          self.tx = tx or Transaction([], [])
          self.nin = nin or 0
          self.flags = flags or 0
  
          return False
  
      # Interpreter constants
      true = Buffer([1])
      false = Buffer([])
  
      MAX_SCRIPT_ELEMENT_SIZE = 520
      LOCKTIME_THRESHOLD = 500000000
  
      # Flags taken from bitcoind
      # bitcoind commit: b5d1b1092998bc95313856d535c632ea5a8f9104
      SCRIPT_VERIFY_NONE = 0
  
      # Evaluate P2SH subscripts (softfork safe, BIP16).
      SCRIPT_VERIFY_P2SH = 1 << 0
  
      # Passing a non-strict-DER signature or one with undefined hashtype to a checksig operation causes script failure.
      # Passing a pubkey that is not (0x04 + 64 bytes) or (0x02 or 0x03 + 32 bytes) to checksig causes that pubkey to be
      # skipped (not softfork safe: this flag can widen the validity of OP_CHECKSIG OP_NOT).
      SCRIPT_VERIFY_STRICTENC = 1 << 1
  
      # Passing a non-strict-DER signature to a checksig operation causes script failure (softfork safe, BIP62 rule 1)
      SCRIPT_VERIFY_DERSIG = 1 << 2
  
      # Passing a non-strict-DER signature or one with S > order/2 to a checksig operation causes script failure
      # (softfork safe, BIP62 rule 5).
      SCRIPT_VERIFY_LOW_S = 1 << 3
  
      # Verify dummy stack item consumed by CHECKMULTISIG is of zero-length (softfork safe, BIP62 rule 7).
      SCRIPT_VERIFY_NULLDUMMY = 1 << 4
  
      # Using a non-push operator in the scriptSig causes script failure (softfork safe, BIP62 rule 2).
      SCRIPT_VERIFY_SIGPUSHONLY = 1 << 5
  
      # Require minimal encodings for all push operations (OP_0... OP_16, OP_1NEGATE where possible, direct
      # pushes up to 75 bytes, OP_PUSHDATA up to 255 bytes, OP_PUSHDATA2 for anything larger). Evaluating
      # any other push causes the script to fail (BIP62 rule 3).
      # In addition, whenever a stack element is interpreted as a number, it must be of minimal length (BIP62 rule 4).
      # (softfork safe)
      SCRIPT_VERIFY_MINIMALDATA = 1 << 6
  
      # Discourage use of NOPs reserved for upgrades (NOP1-10)
      #
      # Provided so that nodes can avoid accepting or mining transactions
      # containing executed NOP's whose meaning may change after a soft-fork,
      # thus rendering the script invalid; with this flag set executing
      # discouraged NOPs fails the script. This verification flag will never be
      # a mandatory flag applied to scripts in a block. NOPs that are not
      # executed, e.g.  within an unexecuted IF ENDIF block, are *not* rejected.
      SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_NOPS = 1 << 7
  
      # CLTV See BIP65 for details.
      SCRIPT_VERIFY_CHECKLOCKTIMEVERIFY = 1 << 9
  
subject: add interpreter flags