adding the script.py file and implement the parse ans seriliaza metho…

…d to scipt class

script.py

@@ -0,0 +1,58 @@
+from usefulfunctions import int_to_little_endian , encode_varint , read_varint , little_endian_to_int
+
+class Script:
+
+    def __init__(self, cmds=None):
+        if cmds is None:
+            self.cmds = []
+        else:
+            self.cmds = cmds
+
+    def parse(cls, s):
+        length = read_varint(s)
+        cmds = []
+        count = 0
+        while count < length:
+            current = s.read(1)
+            count += 1
+            currbyte = current[0]
+            if currbyte >= 1 and currbyte <= 75:
+                n = currbyte
+                cmds.append(s.read(n))
+                count += n
+            elif currbyte == 76:
+                l = little_endian_to_int(s.read(1))
+                cmds.append(s.read(l))
+                count += l + 1
+            elif currbyte == 77:
+                l = little_endian_to_int(s.read(2))
+                cmds.append(s.read(l))
+                count += l + 2
+            else:
+                op_code = currbyte
+                cmds.append(op_code)
+        if count != length:
+            raise SyntaxError('parsing script failed')
+        return cls(cmds)
+
+
+    def serialize(self):
+        r = b''
+        for cmd in self.cmds:
+            if type(cmd) == int:
+                r += int_to_little_endian(cmd, 1)
+            else:
+                length = len(cmd)
+                if length < 75:
+                    r += int_to_little_endian(length, 1)
+                elif length > 75 and length < 0x100:
+                    r += int_to_little_endian(76, 1)
+                    r += int_to_little_endian(length, 1)
+                elif length >= 0x100 and length <= 520:
+                    r += int_to_little_endian(77, 1)
+                    r += int_to_little_endian(length, 2)
+                else:
+                    raise ValueError('cmd is not correct file script.py serialization of script ')
+                r += cmd    
+            r = encode_varint(len(r)) + r  
+        return r

tx.py

@@ -3,7 +3,7 @@
 # TxIn 
 # TxOut 
 from usefulfunctions import int_to_little_endian , encode_varint 
-    
+from script import Script 
 class TxOut:
     #this is the basic frame of the
     def __init__(self, amount, script_pubkey):

usefulfunctions.py

@@ -1,3 +1,17 @@
+def little_endian_to_int(b):
+    return int.from_bytes(b, 'little')
+
+def read_varint(s):
+    i = s.read(1)[0]
+    if i == 0xfd:
+        return little_endian_to_int(s.read(2))
+    elif i == 0xfe:
+        return little_endian_to_int(s.read(4))
+    elif i == 0xff:
+        return little_endian_to_int(s.read(8))
+    else:
+        # anything else is just the integer
+        return i
 
 def int_to_little_endian(n, length): # converting the int into the little edian format 
     return n.to_bytes(length, 'little') 
@@ -12,3 +26,4 @@ def encode_varint(i):
         return b'\xfe' + int_to_little_endian(i, 4)
     elif i < 0x10000000000000000:
         return b'\xff' + int_to_little_endian(i, 8)
+