Objects can now be loaded from both mappings, sequences and scalars. Fixes #12

Author: Sylvain MARIE

yamlable/base.py

@@ -6,6 +6,8 @@
 from abc import ABCMeta
 from collections import OrderedDict
 
+from yaml import ScalarNode, SequenceNode, MappingNode
+
 try:
     # Python 2 only:
     from StringIO import StringIO as _StringIO  # type: ignore  # noqa
@@ -27,7 +29,7 @@ def __exit__(self, exception_type, exception_value, traceback):
 import six
 
 try:  # python 3.5+
-    from typing import Union, TypeVar, Dict, Any
+    from typing import Union, TypeVar, Dict, Any, Tuple
 
     Y = TypeVar('Y', bound='AbstractYamlObject')
 
@@ -49,6 +51,30 @@ class AbstractYamlObject(six.with_metaclass(ABCMeta, object)):
     Default implementation uses vars(self) and cls(**dct), but subclasses can override.
     """
 
+    # def __to_yaml_scalar__(self):
+    #     # type: (...) -> Any
+    #     """
+    #     Implementors should transform the object into a scalar containing all information necessary to decode the
+    #     object as a YAML scalar in the future.
+    #
+    #     Default implementation raises an error.
+    #     :return:
+    #     """
+    #     raise NotImplementedError("Please override `__to_yaml_scalar__` if you wish to dump instances of `%s`"
+    #                               " as yaml scalars." % type(self).__name__)
+    #
+    # def __to_yaml_sequence__(self):
+    #     # type: (...) -> Tuple[Any]
+    #     """
+    #     Implementors should transform the object into a tuple containing all information necessary to decode the
+    #     object as a YAML sequence in the future.
+    #
+    #     Default implementation raises an error.
+    #     :return:
+    #     """
+    #     raise NotImplementedError("Please override `__to_yaml_sequence__` if you wish to dump instances of `%s`"
+    #                               " as yaml sequences." % type(self).__name__)
+
     def __to_yaml_dict__(self):
         # type: (...) -> Dict[str, Any]
         """
@@ -67,6 +93,52 @@ def __to_yaml_dict__(self):
         # Default: return vars(self) (Note: no need to make a copy, pyyaml does not modify it)
         return vars(self)
 
+    @classmethod
+    def __from_yaml_scalar__(cls,      # type: Type[Y]
+                             scalar,   # type: Any
+                             yaml_tag  # type: str
+                             ):
+        # type: (...) -> Y
+        """
+        Implementors should transform the given scalar (read from yaml by the pyYaml stack) into an object instance.
+        The yaml tag associated to this object, read in the yaml document, is provided in parameter.
+
+        Note that for YamlAble and YamlObject2 subclasses, if this method is called the yaml tag will already have
+        been checked so implementors do not have to validate it.
+
+        Default implementation returns cls(scalar)
+
+        :param scalar: the yaml scalar
+        :param yaml_tag: the yaml schema id that was used for encoding the object (it has already been checked
+            against is_json_schema_id_supported)
+        :return:
+        """
+        # Default: call constructor with positional arguments
+        return cls(scalar)  # type: ignore
+
+    @classmethod
+    def __from_yaml_sequence__(cls,      # type: Type[Y]
+                               seq,      # type: Tuple[Any]
+                               yaml_tag  # type: str
+                               ):
+        # type: (...) -> Y
+        """
+        Implementors should transform the given tuple (read from yaml by the pyYaml stack) into an object instance.
+        The yaml tag associated to this object, read in the yaml document, is provided in parameter.
+
+        Note that for YamlAble and YamlObject2 subclasses, if this method is called the yaml tag will already have
+        been checked so implementors do not have to validate it.
+
+        Default implementation returns cls(*seq)
+
+        :param seq: the yaml sequence
+        :param yaml_tag: the yaml schema id that was used for encoding the object (it has already been checked
+            against is_json_schema_id_supported)
+        :return:
+        """
+        # Default: call constructor with positional arguments
+        return cls(*seq)  # type: ignore
+
     @classmethod
     def __from_yaml_dict__(cls,      # type: Type[Y]
                            dct,      # type: Dict[str, Any]
@@ -200,14 +272,72 @@ def load_yaml(cls,                  # type: Type[Y]
 
 
 def read_yaml_node_as_dict(loader, node):
+    # type: (...) -> OrderedDict
     """
     Utility method to read a yaml node into a dictionary
 
     :param loader:
     :param node:
     :return:
     """
-    loader.flatten_mapping(node)
-    pairs = loader.construct_pairs(node, deep=True)  # 'deep' allows the construction to be complete (inner seq...)
+    # loader.flatten_mapping(node)
+    # pairs = loader.construct_pairs(node, deep=True)  # 'deep' allows the construction to be complete (inner seq...)
+    pairs = loader.construct_mapping(node, deep=True)  # 'deep' allows the construction to be complete (inner seq...)
     constructor_args = OrderedDict(pairs)
     return constructor_args
+
+
+def read_yaml_node_as_sequence(loader, node):
+    # type: (...) -> Tuple
+    """
+    Utility method to read a yaml node into a sequence
+
+    :param loader:
+    :param node:
+    :return:
+    """
+    seq = loader.construct_sequence(node, deep=True)  # 'deep' allows the construction to be complete (inner seq...)
+    return seq
+
+
+def read_yaml_node_as_scalar(loader, node):
+    # type: (...) -> Any
+    """
+    Utility method to read a yaml node into a sequence
+
+    :param loader:
+    :param node:
+    :return:
+    """
+    value = loader.construct_scalar(node)
+    return value
+
+
+def read_yaml_node_as_yamlobject(
+    cls,      # type: Type[AbstractYamlObject]
+    loader,
+    node,     # type: MappingNode
+    yaml_tag  # type: str
+):
+    # type: (...) -> AbstractYamlObject
+    """
+    Default implementation: loads the node as a dictionary and calls __from_yaml_dict__ with this dictionary
+
+    :param loader:
+    :param node:
+    :return:
+    """
+    if isinstance(node, ScalarNode):
+        constructor_args = read_yaml_node_as_scalar(loader, node)
+        return cls.__from_yaml_scalar__(constructor_args, yaml_tag=yaml_tag)  # type: ignore
+
+    elif isinstance(node, SequenceNode):
+        constructor_args = read_yaml_node_as_sequence(loader, node)
+        return cls.__from_yaml_sequence__(constructor_args, yaml_tag=yaml_tag)  # type: ignore
+
+    elif isinstance(node, MappingNode):
+        constructor_args = read_yaml_node_as_dict(loader, node)
+        return cls.__from_yaml_dict__(constructor_args, yaml_tag=yaml_tag)  # type: ignore
+
+    else:
+        raise TypeError("Unknown type of yaml node: %r. Please report this to `yamlable` project." % type(node))

yamlable/main.py

@@ -9,7 +9,8 @@
 import six
 
 try:  # python 3.5+
-    from typing import TypeVar, Callable, Iterable, Any, Tuple, Dict, Set, List
+    from typing import TypeVar, Callable, Iterable, Any, Tuple, Dict, Set, List, Sequence
+
     YA = TypeVar('YA', bound='YamlAble')
     T = TypeVar('T')
 except ImportError:
@@ -20,9 +21,10 @@
 except ImportError:
     pass  # normal for old versions of typing
 
-from yaml import Loader, SafeLoader, Dumper, SafeDumper, MappingNode
+from yaml import Loader, SafeLoader, Dumper, SafeDumper, MappingNode, ScalarNode, SequenceNode
 
-from yamlable.base import AbstractYamlObject, read_yaml_node_as_dict
+from yamlable.base import AbstractYamlObject, read_yaml_node_as_yamlobject, read_yaml_node_as_dict, \
+    read_yaml_node_as_sequence, read_yaml_node_as_scalar
 from yamlable.yaml_objects import YamlObject2
 
 
@@ -231,12 +233,13 @@ def decode_yamlable(loader,
     for clazz in candidates:
         try:
             if clazz.is_yaml_tag_supported(yaml_tag):
-                constructor_args = read_yaml_node_as_dict(loader, node)
-                return clazz.__from_yaml_dict__(constructor_args, yaml_tag=yaml_tag)
+                return read_yaml_node_as_yamlobject(cls=clazz, loader=loader, node=node, yaml_tag=yaml_tag)  # type: ignore
+            else:
+                errors[clazz.__name__] = "yaml tag %r is not supported." % yaml_tag
         except Exception as e:
             errors[clazz.__name__] = e
 
-    raise TypeError("No YamlAble subclass found able to decode object !yamlable/" + yaml_tag + ". Tried classes: "
+    raise TypeError("No YamlAble subclass found able to decode object '!yamlable/" + yaml_tag + "'. Tried classes: "
                     + str(candidates) + ". Caught errors: " + str(errors) + ". "
                     "Please check the value of <cls>.__yaml_tag_suffix__ on these classes. Note that this value may be "
                     "set using @yaml_info() so help(yaml_info) might help too.")
@@ -403,8 +406,22 @@ def decode(cls, loader,
         :return:
         """
         if cls.is_yaml_tag_supported(yaml_tag_suffix):
-            constructor_args = read_yaml_node_as_dict(loader, node)
-            return cls.from_yaml_dict(yaml_tag_suffix, constructor_args, **kwargs)
+            # Note: same as in read_yaml_node_as_yamlobject but different yaml tag handling so code copy
+
+            if isinstance(node, ScalarNode):
+                constructor_args = read_yaml_node_as_scalar(loader, node)
+                return cls.from_yaml_scalar(yaml_tag_suffix, constructor_args, **kwargs)  # type: ignore
+
+            elif isinstance(node, SequenceNode):
+                constructor_args = read_yaml_node_as_sequence(loader, node)
+                return cls.from_yaml_sequence(yaml_tag_suffix, constructor_args, **kwargs)  # type: ignore
+
+            elif isinstance(node, MappingNode):
+                constructor_args = read_yaml_node_as_dict(loader, node)
+                return cls.from_yaml_dict(yaml_tag_suffix, constructor_args, **kwargs)  # type: ignore
+
+            else:
+                raise TypeError("Unknown type of yaml node: %r. Please report this to `yamlable` project." % type(node))
 
     @classmethod
     @abstractmethod
@@ -419,6 +436,40 @@ def is_yaml_tag_supported(cls,
         :return:
         """
 
+    @classmethod
+    def from_yaml_scalar(cls,
+                         yaml_tag_suffix,  # type: str
+                         scalar,           # type: Any
+                         **kwargs):
+        # type: (...) -> Any
+        """
+        Implementing classes should create an object corresponding to the given yaml tag, using the given YAML scalar.
+
+        :param scalar:
+        :param yaml_tag_suffix:
+        :param kwargs: keyword arguments coming from pyyaml, not sure what you will find here.
+        :return:
+        """
+        raise NotImplementedError("This codec does not support loading objects from scalar. Please override "
+                                  "`from_yaml_scalar` to support this feature.")
+
+    @classmethod
+    def from_yaml_sequence(cls,
+                           yaml_tag_suffix,  # type: str
+                           seq,              # type: Sequence[Any]
+                           **kwargs):
+        # type: (...) -> Any
+        """
+        Implementing classes should create an object corresponding to the given yaml tag, using the given YAML sequence.
+
+        :param seq:
+        :param yaml_tag_suffix:
+        :param kwargs: keyword arguments coming from pyyaml, not sure what you will find here.
+        :return:
+        """
+        raise NotImplementedError("This codec does not support loading objects from sequence. Please override "
+                                  "`from_yaml_sequence` to support this feature.")
+
     @classmethod
     @abstractmethod
     def from_yaml_dict(cls,
@@ -427,8 +478,7 @@ def from_yaml_dict(cls,
                        **kwargs):
         # type: (...) -> Any
         """
-        Implementing classes should create an object corresponding to the given yaml tag, using the given constructor
-        arguments.
+        Implementing classes should create an object corresponding to the given yaml tag, using the given YAML mapping.
 
         :param dct:
         :param yaml_tag_suffix:

yamlable/tests/test_yamlable.py

@@ -58,10 +58,13 @@ def test_yamlable():
     class Foo(YamlAble):
         # __yaml_tag_suffix__ = 'foo'   not needed: we used @yaml_info
 
-        def __init__(self, a, b):
+        def __init__(self, a, b="hey"):
             self.a = a
             self.b = b
 
+        def __repr__(self):
+            return "Foo(a=%r,b=%r)" % (self.a, self.b)
+
         def __eq__(self, other):
             return vars(self) == vars(other)
 
@@ -111,6 +114,25 @@ def close(self):
     # load pyyaml
     assert f == load(y)
 
+    # mapping, sequences and scalar
+    y_map = """
+!yamlable/yaml.tests.Foo
+a: 1
+"""
+    y_seq = """
+!yamlable/yaml.tests.Foo
+- 1
+"""
+    y_scalar = """
+!yamlable/yaml.tests.Foo
+1
+"""
+    assert Foo.loads_yaml(y_map) == Foo(a=1)
+    assert Foo.loads_yaml(y_seq) == Foo(a=1)
+
+    # Important: if we provide a scalar, there will not be any auto-resolver
+    assert Foo.loads_yaml(y_scalar) == Foo(a="1")
+
 
 def test_yamlable_legacy_method_names():
     """ Tests that YamlAbleMixIn works correctly """

yamlable/tests/test_yamlcodec.py

@@ -1,3 +1,5 @@
+import pytest
+
 try:  # python 3.5+
     from typing import Tuple, Any, Iterable, Dict
 except ImportError:
@@ -86,3 +88,40 @@ def to_yaml_dict(cls, obj):
     # load pyyaml
     assert f == load(fy)
     assert b == load(by)
+
+    # load from sequence / scalar
+    by_seq = """!mycodec/yaml.tests.Bar
+- what?
+"""
+    by_scalar = "!mycodec/yaml.tests.Bar what?"
+
+    with pytest.raises(NotImplementedError):
+        load(by_seq)
+
+    with pytest.raises(NotImplementedError):
+        load(by_scalar)
+
+    class MyCodec2(MyCodec):
+        @classmethod
+        def from_yaml_sequence(cls,
+                               yaml_tag_suffix,  # type: str
+                               seq,              # type: Sequence[Any]
+                               **kwargs):
+            # type: (...) -> Any
+            typ = yaml_tags_to_types[yaml_tag_suffix]
+            return typ(*seq)
+
+        @classmethod
+        def from_yaml_scalar(cls,
+                             yaml_tag_suffix,  # type: str
+                             scalar,           # type: Any
+                             **kwargs):
+            # type: (...) -> Any
+            typ = yaml_tags_to_types[yaml_tag_suffix]
+            return typ(scalar)
+
+    # register the codec
+    MyCodec2.register_with_pyyaml()
+
+    assert b == load(by_seq)
+    assert b == load(by_scalar)