disas: move arg check in main

1 files changed, 7 insertions, 6 deletions

diff --git a/nandgame/assembler/disas.py b/nandgame/assembler/disas.py
index 03d3503..4994a69 100755
--- a/nandgame/assembler/disas.py
+++ b/nandgame/assembler/disas.py
@@ -2,10 +2,6 @@
 
 import sys
 
-if len(sys.argv) != 2:
-    print(f"Usage: {sys.argv[0]} [filename]")
-    sys.exit(1)
-
 
 def decode_jump(ins: int) -> str:
     if (ins & 0x7) == 0:
@@ -133,8 +129,13 @@ def decode(ins: int) -> str:
 
 
 def main():
+    if len(sys.argv) != 2:
+        print(f"Usage: {sys.argv[0]} [filename]")
+        sys.exit(1)
+
     try:
-        with open(sys.argv[1], "rb") as f:
+        filename = sys.argv[1]
+        with open(filename, "rb") as f:
             while True:
                 insb = f.read(2)
                 if not insb:
@@ -143,7 +144,7 @@ def main():
                 print(f"\t{insb[0]:02x} {insb[1]:02x}\t{decode(ins)}")
 
     except FileNotFoundError:
-        print(f"File not found.")
+        print(f"File {filename} not found.")
         sys.exit(1)
     # head, tail...
     except BrokenPipeError: