Fix bug with binary.

compiler.py

@@ -24,6 +24,8 @@
 #   P - Operand (only there if M is 01)
 #
 
+from sys import stdin, stdout, argv, exit
+
 class Data:
     def __init__(self, string):
         self.length = len(string) // 4
@@ -43,8 +45,12 @@ class Data:
         """
         Convert the instruction to a binary string.
         """
-        code = [bin(x)[2:] for x in self.data]
-        return "".join(('0' * (WORD_SIZE - len(x))) + x for x in code)
+        result = []
+        for x in self.data:
+            c = bin(x)[2:]
+            result.append(('0' * (4 - len(c))) + c)
+        return "".join(result)
+
 
 class Instruction:
     """
@@ -105,10 +111,11 @@ class Instruction:
         if self.length == 1:
             length = WORD_SIZE // 1
         else:
-            length = WORD_SIZE // 2
+            length = WORD_SIZE * 2
         code = bin(self.instruction)[2:]
         return ('0' * (length - len(code))) + code
 
+
 OPCODE_TABLE = {   
     "LOAD"  : 0b0000,
     "STORE" : 0b0001,
@@ -137,8 +144,6 @@ REGISTERS = {
 
 WORD_SIZE = 16
 
-from sys import stdin, stdout, argv, exit
-
 output_format = "hex"
 input_file = False
 output_file = False
@@ -232,11 +237,13 @@ def parse_instruction(args):
     return Instruction(opcode, register, mode, address)
 
 
+def main():
     success = True
     line_number = 0 # The line in the source file
     word = 0 # The current word
     instructions = []
     tag_table = {}
+
     for line in input_file:
         line_number += 1
         if "#" in line:
@@ -279,7 +286,7 @@ for instruction in instructions:
             success = False
 
     if not success:
-    exit(1)
+        return 1
 
     def print_as_hex(out, inst, newlines):
         string = instruction.to_hex()
@@ -306,9 +313,12 @@ else:
 
     for instruction in instructions:
         print_func(output_file, instruction, newlines)
+
     output_file.flush()
     output_file.close()
 
-exit(0)
+
+if __name__ == "__main__":
+    exit(main())