-

cool-RR · cool-RR · commit 19f976c94249 · 2014-01-18T14:40:23.000+02:00
diff --git a/misc/IDE files/Wing/python_toolbox_py3.wpr b/misc/IDE files/Wing/python_toolbox_py3.wpr
@@ -34,8 +34,8 @@ proj.directory-list = [{'dirloc': loc('../../..'),
                         'watch_for_changes': True}]
 proj.file-type = 'shared'
 proj.home-dir = loc('../../..')
-proj.launch-config = {loc('../../../../../../Desktop/ultimate.py'): ('projec'\
-        't',
+proj.launch-config = {loc('../../../source_py3/python_toolbox/cute_iter_tools.py'): (''\
+        'project',
         (u'',
          'launch-OHU716PSo2P5T54y'))}
 testing.auto-test-file-specs = [('glob',
diff --git a/source_py3/python_toolbox/file_tools.py b/source_py3/python_toolbox/file_tools.py
@@ -4,6 +4,7 @@
 '''Defines various tools related to temporary files.'''
 
 import pathlib
+import uuid
 import os
 import re
 
@@ -101,8 +102,8 @@ def create_file_renaming_if_taken(path, mode='x',
                                         N_MAX_ATTEMPTS):
         try:
             return path.open(mode, buffering=buffering,
-                                     encoding=encoding, errors=errors,
-                                     newline=newline)
+                             encoding=encoding, errors=errors,
+                             newline=newline)
         except FileExistsError:
             pass
     else:
@@ -126,4 +127,59 @@ def write_to_file_renaming_if_taken(path, data, mode='x',
         newline=newline) as file:
         
         return file.write(data)
-        
+        
+        
+def atomic_create_and_write(path, data=None, binary=False):
+    '''
+    Write data to file, but use a temporary file as a buffer.
+    
+    The data you write to this file is actuall written to a temporary file in
+    the same folder, and only after you close it, without having an exception
+    raised, it renames the temporary file to your original file name. If an
+    exception was raised during writing it deletes the temporary file.
+    
+    This way you're sure you're not getting a half-baked file.
+    '''    
+    with atomic_create(path, binary=binary) as file:
+        return file.write(data)
+
+
+@context_management.ContextManagerType
+def atomic_create(path, binary=False):
+    '''
+    Create a file for writing, but use a temporary file as a buffer.
+    
+    Use as a context manager:
+    
+        with atomic_create(path) as my_file:
+            my_file.write('Whatever')
+    
+    When you write to this file it actually writes to a temporary file in the
+    same folder, and only after you close it, without having an exception
+    raised, it renames the temporary file to your original file name. If an
+    exception was raised during writing it deletes the temporary file.
+    
+    This way you're sure you're not getting a half-baked file.
+    '''
+    path = pathlib.Path(path)
+    if path.exists():
+        raise Exception("There's already a file called %s" % path)
+    desired_temp_file_path = path.parent / ('._%s.tmp' % path.stem)
+    try:
+        with create_file_renaming_if_taken(desired_temp_file_path,
+                                         'xb' if binary else 'x') as temp_file:
+            actual_temp_file_path = pathlib.Path(temp_file.name)
+            yield temp_file
+        
+        # This part runs only if there was no exception when writing to the
+        # file:
+        if path.exists():
+            raise Exception("There's already a file called %s" % path)
+        actual_temp_file_path.rename(path)
+        assert path.exists()
+        
+    finally:
+        if actual_temp_file_path.exists():
+            actual_temp_file_path.unlink()
+            
+
diff --git a/source_py3/test_python_toolbox/test_file_tools/test_atomic.py b/source_py3/test_python_toolbox/test_file_tools/test_atomic.py
@@ -0,0 +1,53 @@
+# Copyright 2009-2014 Ram Rachum.
+# This program is distributed under the MIT license.
+
+import pathlib
+
+import python_toolbox
+from python_toolbox import temp_file_tools
+from python_toolbox import cute_testing
+
+from python_toolbox import file_tools
+
+
+def test():
+    with temp_file_tools.create_temp_folder(
+                            prefix='test_python_toolbox_') as temp_folder:
+        assert set(temp_folder.glob('*')) == set()
+        file_1 = temp_folder / 'file_1.txt'
+        assert not file_1.exists()
+        file_tools.atomic_create_and_write(file_1, "Meow meow I'm a cat.")
+        assert set(temp_folder.glob('*')) == {file_1}
+        with file_1.open('r') as file:
+            assert file.read() == "Meow meow I'm a cat."
+        
+        #######################################################################
+        
+        file_2 = temp_folder / 'file_2.txt'
+        with file_tools.atomic_create(file_2) as file:
+            file.write('Hurr durr')
+            assert not file_2.exists()
+            assert len(set(temp_folder.glob('*'))) == 2
+            
+        assert file_2.exists()
+        assert len(set(temp_folder.glob('*'))) == 2            
+        assert set(temp_folder.glob('*')) == {file_1, file_2}
+        with file_2.open('r') as file:
+            assert file.read() == 'Hurr durr'
+            
+        #######################################################################
+            
+
+        file_3 = temp_folder / 'file_3.txt'
+        
+        with cute_testing.RaiseAssertor(ZeroDivisionError):
+            with file_tools.atomic_create(file_3) as file:
+                file.write('bloop bloop bloop')
+                assert not file_3.exists()
+                assert len(set(temp_folder.glob('*'))) == 3
+                1 / 0
+            
+        assert not file_3.exists()
+        assert len(set(temp_folder.glob('*'))) == 2            
+        assert set(temp_folder.glob('*')) == {file_1, file_2}
+        
