Low s canonical signature for bitcoin transaction

Question

I have a transaction script and trying to make it so that it has a canonical low_s signature for validation purposes. Here is the script:

import __future__

import hashlib

import pycoin
from pycoin.ecdsa import *
 
import string
import array
import binascii

def rev(str):
    ret = ""
    for i in range(0, len(str), 2):
        ret = str[i:i+2] + ret
    return ret
 
def revbyfours(s):
    res = ""
    for i in range(int(len(s)/8)):
        res += rev(s[8*i:8*i+8])
    return res
 
def verify_sig(sig, prefix, xpub, signed_val):
    is_even = (prefix % 2 == 0)
    pub_pair = public_pair_for_x(generator_secp256k1, xpub, is_even)
    print("sig: (" + hex(sig[0])      + ", " + hex(sig[1])      + ")")
    print("pub: (" + hex(pub_pair[0]) + ", " + hex(pub_pair[1]) + ")")
    print("hex: "  + hex(signed_val))
 
    print("is valid: " + str(verify(generator_secp256k1, pub_pair, signed_val, sig)))
 
def DoubleHash(string):
    bin = binascii.unhexlify(string)
    hash = hashlib.sha256(hashlib.sha256(bin).digest()).digest()
    raw = str(binascii.hexlify(hash))[2:-1]
    return rev(raw)
 
def DER(r, s):
    rlen = int(len(r)/2)
    if (rlen == 32 and int(r[0:2], 16) > 0x7F):
        rlen += 1
   
    slen = int(len(s)/2)              
    if (slen == 32 and int(s[0:2], 16) > 0x7F):
        slen += 1
   
    res = "30"
    res += hex(4 + rlen + slen)[2:].zfill(2)
    res += "02"
    res += hex(rlen)[2:].zfill(2)
    res += r
    res += "02"
    res += hex(slen)[2:].zfill(2)
    res += s
    return res

addr     = 'zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz'
pubkey_x = 0xzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz
pubkey_y = 0xzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz

rawtx = '0100000001............................................88ac00000000'
 
# replacing the '00' scriptSig value
unsigned = ""
 
unsigned += rawtx[:82]
print (unsigned)
 
unsigned += '19'+'76a914zzzzzzzzzzzzzzzzzzzzzzzzzzzzz88ac' # scriptSig = scriptPubKey input
print (unsigned)
 
unsigned += rawtx[84:]
print (unsigned)
 
unsigned += '01000000'  # appending sighash_all
print (unsigned)
 
unsigned = ''.join(unsigned)
print (unsigned)
 
unsigned = '0100000001....................................................................e88ac0000000001000000'
 
# hashToSign
s256 = hashlib.sha256(hashlib.sha256(unsigned_forSig.decode('hex')).digest()).digest()

 
print ("hash: " + s256)

priv = ecdsa.SigningKey.generate(curve=ecdsa.SECP256k1
 
sig = sk.sign_digest(s256, sigencode=ecdsa.util.sigencode_der)
 
#r = hex(sig[0])[2:]
#s = hex(sig[1])[2:]
 
print ("r: " + r)
print ("s: " + s)
 
derSig = DER(r, s) + "01" # 01 is for sighashall

#these are other options to use
#derSig = hex(int(len(derSig)/2))[2:].zfill(2) + derSig
#sigencode=ecdsa.util.sigencode_der
#sk.sign_digest_deterministic(hash, hashfunc=hashlib.sha256, sigencode=sigencode_string_canonize)

 
print ("der: " + derSig) #prints out the signature with the DER encoding

# note how the pushdata is in front of the uncompressed pubkey
pub = "4104zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz957bedfb6"
# inserting the signature into the 00 the core software uses in place of ScriptSig
# this prints out a signed raw hexadecimal txn
signed = rawtx[:82] + hex(int(len(derSig + pub)/2))[2:].zfill(2) + derSig + pub + rawtx[84:]
 
print ("signed: " + signed)

unsigned = '0100000001...........................................88ac0000000001000000'
 
# note how the pushdata is in front of the uncompressed pubkey
pub = "4104zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz7bedfb6"
# inserting the signature into the 00 the core software uses in place of ScriptSig
# this prints out a signed raw hexadecimal txn
signed = rawtx[:82] + hex(int(len(derSig + pub)/2))[2:].zfill(2) + derSig + pub + rawtx[84:]
 
print ("signed: " + signed)