Merge pull request #613 from minrk/from-string-none

handle allow_none in from_string

traitlets/config/tests/test_application.py

@@ -295,6 +295,15 @@ class TestApp(Application):
             assert app.config.TestApp.value == 'cli'
             assert app.value == 'cli'
 
+    def test_cli_allow_none(self):
+        class App(Application):
+            aliases = {"opt": "App.opt"}
+            opt = Unicode(allow_none=True, config=True)
+
+        app = App()
+        app.parse_command_line(["--opt=None"])
+        assert app.opt is None
+
     def test_flags(self):
         app = MyApp()
         app.parse_command_line(["--disable"])

traitlets/tests/test_traitlets.py

@@ -2658,7 +2658,7 @@ def _from_string_test(traittype, s, expected):
     if isinstance(traittype, TraitType):
         trait = traittype
     else:
-        trait = traittype()
+        trait = traittype(allow_none=True)
     if isinstance(s, list):
         cast = trait.from_string_list
     else:
@@ -2673,107 +2673,133 @@ def _from_string_test(traittype, s, expected):
 
 
 @pytest.mark.parametrize(
-    "s, expected", [("xyz", "xyz"), ("1", "1"), ('"xx"', "xx"), ("'abc'", "abc"),]
+    "s, expected",
+    [("xyz", "xyz"), ("1", "1"), ('"xx"', "xx"), ("'abc'", "abc"), ("None", None)],
 )
 def test_unicode_from_string(s, expected):
     _from_string_test(Unicode, s, expected)
 
 
 @pytest.mark.parametrize(
-    "s, expected", [("xyz", "xyz"), ("1", "1"), ('"xx"', "xx"), ("'abc'", "abc"),]
+    "s, expected",
+    [("xyz", "xyz"), ("1", "1"), ('"xx"', "xx"), ("'abc'", "abc"), ("None", None)],
 )
 def test_cunicode_from_string(s, expected):
     _from_string_test(CUnicode, s, expected)
 
 
-@pytest.mark.parametrize('s, expected', [
-    ('x', ValueError),
-    ('1', 1),
-    ('123', 123),
-    ('2.0', ValueError),
-])
+@pytest.mark.parametrize(
+    "s, expected",
+    [("x", ValueError), ("1", 1), ("123", 123), ("2.0", ValueError), ("None", None)],
+)
 def test_int_from_string(s, expected):
     _from_string_test(Integer, s, expected)
 
 
-@pytest.mark.parametrize('s, expected', [
-    ('x', ValueError),
-    ('1', 1.0),
-    ('123.5', 123.5),
-    ('2.5', 2.5),
-])
+@pytest.mark.parametrize(
+    "s, expected",
+    [("x", ValueError), ("1", 1.0), ("123.5", 123.5), ("2.5", 2.5), ("None", None)],
+)
 def test_float_from_string(s, expected):
     _from_string_test(Float, s, expected)
 
 
-@pytest.mark.parametrize('s, expected', [
-    ('x', ValueError),
-    ('1', 1.0),
-    ('123.5', 123.5),
-    ('2.5', 2.5),
-    ('1+2j', 1+2j),
-])
+@pytest.mark.parametrize(
+    "s, expected",
+    [
+        ("x", ValueError),
+        ("1", 1.0),
+        ("123.5", 123.5),
+        ("2.5", 2.5),
+        ("1+2j", 1 + 2j),
+        ("None", None),
+    ],
+)
 def test_complex_from_string(s, expected):
     _from_string_test(Complex, s, expected)
 
 
-@pytest.mark.parametrize('s, expected', [
-    ('true', True),
-    ('TRUE', True),
-    ('1', True),
-    ('0', False),
-    ('False', False),
-    ('false', False),
-    ('1.0', ValueError),
-])
+@pytest.mark.parametrize(
+    "s, expected",
+    [
+        ("true", True),
+        ("TRUE", True),
+        ("1", True),
+        ("0", False),
+        ("False", False),
+        ("false", False),
+        ("1.0", ValueError),
+        ("None", None),
+    ],
+)
 def test_bool_from_string(s, expected):
     _from_string_test(Bool, s, expected)
 
 
-@pytest.mark.parametrize('s, expected', [
-    ('{}', {}),
-    ('1', TraitError),
-    ('{1: 2}', {1: 2}),
-    ('{"key": "value"}', {"key": "value"}),
-    ('x', TraitError),
-])
+@pytest.mark.parametrize(
+    "s, expected",
+    [
+        ("{}", {}),
+        ("1", TraitError),
+        ("{1: 2}", {1: 2}),
+        ('{"key": "value"}', {"key": "value"}),
+        ("x", TraitError),
+        ("None", None),
+    ],
+)
 def test_dict_from_string(s, expected):
     _from_string_test(Dict, s, expected)
 
 
-@pytest.mark.parametrize('s, expected', [
-    ('[]', []),
-    ('[1, 2, "x"]', [1, 2, 'x']),
-    (["1", "x"], ["1", "x"])
-])
+@pytest.mark.parametrize(
+    "s, expected",
+    [
+        ("[]", []),
+        ('[1, 2, "x"]', [1, 2, "x"]),
+        (["1", "x"], ["1", "x"]),
+        (["None"], None),
+    ],
+)
 def test_list_from_string(s, expected):
     _from_string_test(List, s, expected)
 
 
-@pytest.mark.parametrize('s, expected, value_trait', [
-    (["1", "2", "3"], [1, 2, 3], Integer()),
-    (["x"], ValueError, Integer()),
-    (["1", "x"], ["1", "x"], Unicode())
-])
-def test_list_from_string(s, expected, value_trait):
+@pytest.mark.parametrize(
+    "s, expected, value_trait",
+    [
+        (["1", "2", "3"], [1, 2, 3], Integer()),
+        (["x"], ValueError, Integer()),
+        (["1", "x"], ["1", "x"], Unicode()),
+        (["None"], [None], Unicode(allow_none=True)),
+    ],
+)
+def test_list_items_from_string(s, expected, value_trait):
     _from_string_test(List(value_trait), s, expected)
 
 
-@pytest.mark.parametrize('s, expected', [
-    ('x', 'x'),
-    ('mod.submod', 'mod.submod'),
-    ('not an identifier', TraitError),
-    ('1', '1'),
-])
+@pytest.mark.parametrize(
+    "s, expected",
+    [
+        ("x", "x"),
+        ("mod.submod", "mod.submod"),
+        ("not an identifier", TraitError),
+        ("1", "1"),
+        ("None", None),
+    ],
+)
 def test_object_from_string(s, expected):
     _from_string_test(DottedObjectName, s, expected)
 
 
-@pytest.mark.parametrize('s, expected', [
-    ('127.0.0.1:8000', ('127.0.0.1', 8000)),
-    ('host.tld:80', ('host.tld', 80)),
-    ('host:notaport', ValueError),
-    ('127.0.0.1', ValueError),
-])
+@pytest.mark.parametrize(
+    "s, expected",
+    [
+        ("127.0.0.1:8000", ("127.0.0.1", 8000)),
+        ("host.tld:80", ("host.tld", 80)),
+        ("host:notaport", ValueError),
+        ("127.0.0.1", ValueError),
+        ("None", None),
+    ],
+)
 def test_tcp_from_string(s, expected):
     _from_string_test(TCPAddress, s, expected)

traitlets/traitlets.py

@@ -493,6 +493,8 @@ def from_string(self, s):
 
         .. versionadded:: 5.0
         """
+        if self.allow_none and s == 'None':
+            return None
         return s
 
     def default(self, obj=None):
@@ -2038,6 +2040,8 @@ def validate(self, obj, value):
         return _validate_bounds(self, obj, value)
 
     def from_string(self, s):
+        if self.allow_none and s == 'None':
+            return None
         return int(s)
 
 
@@ -2076,6 +2080,8 @@ def validate(self, obj, value):
         return _validate_bounds(self, obj, value)
 
     def from_string(self, s):
+        if self.allow_none and s == 'None':
+            return None
         return float(s)
 
 
@@ -2104,6 +2110,8 @@ def validate(self, obj, value):
         self.error(obj, value)
 
     def from_string(self, s):
+        if self.allow_none and s == 'None':
+            return None
         return complex(s)
 
 
@@ -2131,6 +2139,8 @@ def validate(self, obj, value):
         self.error(obj, value)
 
     def from_string(self, s):
+        if self.allow_none and s == 'None':
+            return None
         return s.encode('utf8')
 
 
@@ -2162,6 +2172,8 @@ def validate(self, obj, value):
         self.error(obj, value)
 
     def from_string(self, s):
+        if self.allow_none and s == 'None':
+            return None
         s = os.path.expanduser(s)
         if len(s) >= 2:
             # handle deprecated "1"
@@ -2203,6 +2215,8 @@ def validate(self, obj, value):
         self.error(obj, value)
 
     def from_string(self, s):
+        if self.allow_none and s == 'None':
+            return None
         return s
 
 class DottedObjectName(ObjectName):
@@ -2233,6 +2247,8 @@ def validate(self, obj, value):
         self.error(obj, value)
 
     def from_string(self, s):
+        if self.allow_none and s == 'None':
+            return None
         s = s.lower()
         if s in {'true', '1'}:
             return True
@@ -2487,6 +2503,8 @@ def from_string_list(self, s_list):
         if len(s_list) == 1:
             # check for deprecated --Class.trait="['a', 'b', 'c']"
             r = s_list[0]
+            if r == "None" and self.allow_none:
+                return None
             if (
                 (r[0] == '[' and r[-1] == ']') or
                 (r[0] == '(' and r[-1] == ')')
@@ -2897,6 +2915,8 @@ def from_string_list(self, s_list):
 
         This is where we parse CLI configuration
         """
+        if len(s_list) == 1 and s_list[0] == "None" and self.allow_none:
+            return None
         if (
             len(s_list) == 1
             and s_list[0].startswith("{")
@@ -2965,6 +2985,8 @@ def validate(self, obj, value):
         self.error(obj, value)
 
     def from_string(self, s):
+        if self.allow_none and s == 'None':
+            return None
         if ':' not in s:
             raise ValueError('Require `ip:port`, got %r' % s)
         ip, port = s.split(':', 1)