def __init__(self):

self.inputs = []

self.outputs = []

self.sigs = []

self.reqd = []

def add_input(self, from_addr, amount):

"""Adds input into the Tx"""

self.inputs.append((from_addr, amount))

def add_output(self, to_addr, amount):

"""Adds output into the Tx"""

self.outputs.append((to_addr, amount))

def add_reqd(self, addr):

"""Adds required escrow signature into the Tx"""

self.reqd.append(addr)

def sign(self, private):

"""Signs the transactions with the private key"""

message = self.__gather()

newsigs = sign(message, private)

self.sigs.append(newsigs)

def is_valid(self):

"""Validates data in the transaction"""

data = self.__gather()

total_in = 0

total_out = 0

for address, amount in self.inputs:

found = False

for signature in self.sigs:

if verify(data, signature, address):

found = True

if not found:

return False

if amount < 0:

return False

total_in += amount

for address in self.reqd:

found = False

for signature in self.sigs:

if verify(data, signature, address):

found = True

if not found:

return False

for address, amount in self.outputs:

if amount < 0:

return False

total_out += amount

if total_out > total_in:

return False

return True

def __repr__ (self):

repr_str = "INPUTS: \n"

for address, amount in self.inputs:

repr_str += "\t" + str(amount) + " from " + str(address) +"\n"

repr_str = "OUTPUS: \n"

for address, amount in self.outputs:

repr_str += "\t" + str(amount) + " to " + str(address) + "\n"

repr_str = "ESCROW SIGNATURES: \n"

for r in self.reqd:

repr_str += "\t" + str(r) + "\n"

repr_str = "SIGNATURES: \n"

for s in self.sigs:

repr_str += "\t" + str(s) + "\n"

return repr_str

def __gather(self):

data = []

data.append(self.inputs)

data.append(self.outputs)

data.append(self.reqd)