Issue #22826: The result of open() in Tools/freeze/bkfile.py is now better

compatible with regular files (in particular it now supports the context
management protocol).

Misc/NEWS

@@ -89,6 +89,14 @@ Build
 
 - Issue #23585: make patchcheck will ensure the interpreter is built.
 
+Tools/Demos
+-----------
+
+- Issue #22826: The result of open() in Tools/freeze/bkfile.py is now better
+  compatible with regular files (in particular it now supports the context
+  management protocol).
+
+
 What's New in Python 3.5 alpha 2?
 =================================
 

Tools/freeze/bkfile.py

@@ -1,49 +1,26 @@
 from builtins import open as _orig_open
 
-class _BkFile:
-    def __init__(self, file, mode, bufsize):
-        import os
-        self.__filename = file
-        self.__backup = file + '~'
-        try:
-            os.unlink(self.__backup)
-        except OSError:
-            pass
-        try:
-            os.rename(file, self.__backup)
-        except OSError:
-            self.__backup = None
-        self.__file = _orig_open(file, mode, bufsize)
-        self.closed = self.__file.closed
-        self.fileno = self.__file.fileno
-        self.flush = self.__file.flush
-        self.isatty = self.__file.isatty
-        self.mode = self.__file.mode
-        self.name = self.__file.name
-        self.read = self.__file.read
-        try:
-            self.readinto = self.__file.readinto
-        except AttributeError:
-            pass
-        self.readline = self.__file.readline
-        self.readlines = self.__file.readlines
-        self.seek = self.__file.seek
-        self.tell = self.__file.tell
-        self.truncate = self.__file.truncate
-        self.write = self.__file.write
-        self.writelines = self.__file.writelines
-
-    def close(self):
-        self.__file.close()
-        if self.__backup is None:
-            return
-        import filecmp
-        if filecmp.cmp(self.__backup, self.__filename, shallow = 0):
-            import os
-            os.unlink(self.__filename)
-            os.rename(self.__backup, self.__filename)
-
-def open(file, mode = 'r', bufsize = -1):
+def open(file, mode='r', bufsize=-1):
     if 'w' not in mode:
         return _orig_open(file, mode, bufsize)
-    return _BkFile(file, mode, bufsize)
+    import os
+    backup = file + '~'
+    try:
+        os.unlink(backup)
+    except OSError:
+        pass
+    try:
+        os.rename(file, backup)
+    except OSError:
+        return _orig_open(file, mode, bufsize)
+    f = _orig_open(file, mode, bufsize)
+    _orig_close = f.close
+    def close():
+        _orig_close()
+        import filecmp
+        if filecmp.cmp(backup, file, shallow=False):
+            import os
+            os.unlink(file)
+            os.rename(backup, file)
+    f.close = close
+    return f

Tools/freeze/freeze.py

@@ -439,25 +439,17 @@ def main():
                  frozendllmain_c, os.path.basename(extensions_c)] + files
         maindefn = checkextensions_win32.CExtension( '__main__', xtras )
         frozen_extensions.append( maindefn )
-        outfp = open(makefile, 'w')
-        try:
+        with open(makefile, 'w') as outfp:
             winmakemakefile.makemakefile(outfp,
                                          locals(),
                                          frozen_extensions,
                                          os.path.basename(target))
-        finally:
-            outfp.close()
         return
 
     # generate config.c and Makefile
     builtins.sort()
-    infp = open(config_c_in)
-    outfp = bkfile.open(config_c, 'w')
-    try:
+    with open(config_c_in) as infp, bkfile.open(config_c, 'w') as outfp:
         makeconfig.makeconfig(infp, outfp, builtins)
-    finally:
-        outfp.close()
-    infp.close()
 
     cflags = ['$(OPT)']
     cppflags = defines + includes
@@ -475,11 +467,8 @@ def main():
             files + supp_sources +  addfiles + libs + \
             ['$(MODLIBS)', '$(LIBS)', '$(SYSLIBS)']
 
-    outfp = bkfile.open(makefile, 'w')
-    try:
+    with bkfile.open(makefile, 'w') as outfp:
         makemakefile.makemakefile(outfp, somevars, files, base_target)
-    finally:
-        outfp.close()
 
     # Done!
 

Tools/freeze/makefreeze.py

@@ -39,7 +39,7 @@ def makefreeze(base, dict, debug=0, entry_point=None, fail_import=()):
         mangled = "__".join(mod.split("."))
         if m.__code__:
             file = 'M_' + mangled + '.c'
-            outfp = bkfile.open(base + file, 'w')
+            with bkfile.open(base + file, 'w') as outfp:
                 files.append(file)
                 if debug:
                     print("freezing", mod, "...")
@@ -50,10 +50,9 @@ def makefreeze(base, dict, debug=0, entry_point=None, fail_import=()):
                     size = -size
                 done.append((mod, mangled, size))
                 writecode(outfp, mangled, str)
-            outfp.close()
     if debug:
         print("generating table of frozen modules")
-    outfp = bkfile.open(base + 'frozen.c', 'w')
+    with bkfile.open(base + 'frozen.c', 'w') as outfp:
         for mod, mangled, size in done:
             outfp.write('extern unsigned char M_%s[];\n' % mangled)
         outfp.write(header)
@@ -68,7 +67,6 @@ def makefreeze(base, dict, debug=0, entry_point=None, fail_import=()):
             outfp.write('\t{"%s", NULL, 0},\n' % (mod,))
         outfp.write(trailer)
         outfp.write(entry_point)
-    outfp.close()
     return files