backups are important

Akuli · Akuli · commit 0d2a3562aa02 · 2017-01-31T19:37:24.000+02:00
diff --git a/common.py b/common.py
@@ -31,9 +31,11 @@
 file when actually opening files.
 """
 
+import contextlib
 import itertools
 import os
 import re
+import shutil
 
 
 _LINK_REGEX = r'\[(.*?)\]\((.*?)\)'
@@ -108,3 +110,17 @@ def slashfix(path):
 def slashfix_open(file, mode):
     """An easy way to use slashfix() and open() together."""
     return open(slashfix(file), mode)
+
+
+@contextlib.contextmanager
+def backup(filename):
+    """A context manager that backs up a file."""
+    shutil.copy(filename, filename + '.backup')
+    try:
+        yield
+    except Exception:
+        # It failed, we need to restore from the backup.
+        shutil.copy(filename + '.backup', filename)
+    else:
+        # Everything's fine, we can safely get rid of the backup.
+        os.remove(filename + '.backup')
diff --git a/strip.py b/strip.py
@@ -45,23 +45,21 @@ def needs_stripping(file):
 
 
 def strip(file):
+    real_file = common.slashfix(file)
     lines = []
-    with common.slashfix_open(file, 'r') as f:
+    with open(real_file, 'r') as f:
         for line in f:
-            line = line.rstrip('\n')
-            # it's important to do as much as possible here because the
-            # file may be lost if writing fails, that's why fix() is
-            # here
-            lines.append(fix(line))
-    with common.slashfix_open(file, 'w') as f:
-        for line in lines:
-            print(line, file=f)
+            lines.append(fix(line.rstrip('\n')))
+    with common.backup(real_file):
+        with open(real_file, 'w') as f:
+            for line in lines:
+                print(line, file=f)
 
 
 def main():
     for file in common.get_markdown_files():
         if needs_stripping(file):
-            print("Stripping", file)
+            print("Stripping", file, "...")
             strip(file)
         else:
             print("No trailing whitespace or tabs in", file)
