Add TOML support

setup.py

@@ -108,7 +108,8 @@
 ]
 
 extras_require = setuptools_args['extras_require'] = {
-    'test': ['pytest'],
+    'test': ['pytest', 'toml'],
+    'with-toml': ['toml'],
 }
 
 if 'setuptools' in sys.modules:

traitlets/config/loader.py

@@ -9,6 +9,11 @@
 import re
 import sys
 import json
+try:
+    import toml
+    HAS_TOML = True
+except ImportError:
+    HAS_TOML = None
 import warnings
 
 from ..utils import cast_unicode
@@ -543,6 +548,7 @@ def _find_file(self):
         """Try to find the file by searching the paths."""
         self.full_filename = filefind(self.filename, self.path)
 
+
 class JSONFileConfigLoader(FileConfigLoader):
     """A JSON file loader for config
 
@@ -598,6 +604,69 @@ def __exit__(self, exc_type, exc_value, traceback):
             f.write(json_config)
 
 
+class TOMLFileConfigLoader(FileConfigLoader):
+    """A TOML file loader for config
+
+    Can also act as a context manager that rewrite the configuration file to disk on exit.
+
+    Example::
+
+        with TOMLFileConfigLoader('myapp.toml','/home/jupyter/configurations/') as c:
+            c.MyNewConfigurable.new_value = 'Updated'
+
+    """
+
+    def __init__(self, filename, **kw):
+        """Wrapper for checking (optional) toml module import"""
+        if not HAS_TOML:
+            raise ConfigLoaderError('toml module is not found. In order to use toml configuration'
+                                    'files, please either install traitlets with corresponding option'
+                                    ' (pip install "traitlets[with-toml]") or simply add it with'
+                                    '"pip install toml"')
+        super(TOMLFileConfigLoader, self).__init__(filename, **kw)
+
+    def load_config(self):
+        """Load the config from a file and return it as a Config object."""
+        self.clear()
+        try:
+            self._find_file()
+        except IOError as e:
+            raise ConfigFileNotFound(str(e))
+        dct = self._read_file_as_dict()
+        self.config = self._convert_to_config(dct)
+        return self.config
+
+    def _read_file_as_dict(self):
+        with open(self.full_filename) as f:
+            return toml.load(f)
+
+    def _convert_to_config(self, dictionary):
+        if 'version' in dictionary:
+            version = dictionary.pop('version')
+        else:
+            version = 1
+
+        if version == 1:
+            return Config(dictionary)
+        else:
+            raise ValueError('Unknown version of TOML config file: {version}'.format(version=version))
+
+    def __enter__(self):
+        self.load_config()
+        return self.config
+
+    def __exit__(self, exc_type, exc_value, traceback):
+        """
+        Exit the context manager but do not handle any errors.
+
+        In case of any error, we do not want to write the potentially broken
+        configuration to disk.
+        """
+        self.config.version = 1
+        toml_config = toml.dumps(self.config)
+        with open(self.full_filename, 'w') as f:
+            f.write(toml_config)
+
 
 class PyFileConfigLoader(FileConfigLoader):
     """A config loader for pure python files.

traitlets/config/tests/test_loader.py

@@ -18,6 +18,7 @@
     LazyConfigValue,
     PyFileConfigLoader,
     JSONFileConfigLoader,
+    TOMLFileConfigLoader,
     KeyValueConfigLoader,
     ArgParseConfigLoader,
     KVArgParseConfigLoader,
@@ -69,6 +70,27 @@
 }
 """
 
+toml_file = """
+# This is a TOML document.
+
+version = 1
+
+a = 10
+b = 20
+
+[Foo]
+  # Indentation (tabs and/or spaces) is allowed but not required
+  [Foo.Bam]
+    value = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+
+  [Foo.Bar]
+    value = 10
+
+[D]
+  [D.C]
+    value = 'hi there'
+"""
+
 import logging
 log = logging.getLogger('devnull')
 log.setLevel(0)
@@ -102,6 +124,32 @@ def test_json(self):
         config = cl.load_config()
         self._check_conf(config)
 
+    def test_toml(self):
+        fd, fname = mkstemp('.toml', prefix='μnïcø∂e')
+        f = os.fdopen(fd, 'w')
+        f.write(toml_file)
+        f.close()
+        # Unlink the file
+        cl = TOMLFileConfigLoader(fname, log=log)
+        config = cl.load_config()
+        self._check_conf(config)
+
+    def test_optional_toml(self):
+        import traitlets.config.loader as loader
+        from traitlets.config.loader import ConfigLoaderError
+        loader.HAS_TOML = False
+        fd, fname = mkstemp('.toml', prefix='μnïcø∂e')
+        f = os.fdopen(fd, 'w')
+        f.write(toml_file)
+        f.close()
+        error_raised = False
+        try:
+            cl = TOMLFileConfigLoader(fname, log=log)
+        except ConfigLoaderError:
+            error_raised = True
+        loader.HAS_TOML = True
+        assert error_raised is True
+
     def test_context_manager(self):
 
         fd, fname = mkstemp('.json', prefix='μnïcø∂e')