From 7936f15f27dad0c24d856a56c3a7e278413b8b52 Mon Sep 17 00:00:00 2001
From: Ethan Dalool <git@voussoir.net>
Date: Tue, 25 May 2021 01:34:06 -0700
Subject: [PATCH] Don't let output file be one of the input files.

---
 bitwise_or.py | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/bitwise_or.py b/bitwise_or.py
index 79a109b..a629b71 100644
--- a/bitwise_or.py
+++ b/bitwise_or.py
@@ -31,13 +31,15 @@ def bitwise_or_argparse(args):
         log.fatal('Need at least two input files.')
         return 1
 
-    handles = [file.open('rb') for file in files]
-
     output = pathclass.Path(args.output)
     if output.is_dir:
         log.fatal('Output path "%s" is a directory.', args.output)
         return 1
 
+    if any(output == file for file in files):
+        log.fatal('Output cannot be one of the inputs.')
+        return 1
+
     if not output.exists:
         pass
     elif args.overwrite:
@@ -45,6 +47,7 @@ def bitwise_or_argparse(args):
     elif not interactive.getpermission(f'Overwrite "{output.absolute_path}"?'):
         return 1
 
+    handles = [file.open('rb') for file in files]
     output_handle = output.open('wb')
     while True:
         chunk = 0