added context manager, mypy cleanup (w. Optional) added tests0.15.50

19 files changed, 196 insertions, 83 deletions

diff --git a/CHANGES b/CHANGES
index eadd88a..f9c160f 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,9 @@
+[0, 15, 50]: 2018-08-05
+  - Allow ``YAML()`` as a context manager for output, thereby making it much easier
+    to generate multi-documents in a stream. 
+  - Fix issue with incorrect type information for `load()` and `dump()` (reported 
+    by `Jimbo Jim <https://bitbucket.org/jimbo1qaz/>`__)
+
 [0, 15, 49]: 2018-08-05
   - fix preservation of leading newlines in root level literal style scalar,
     and preserve comment after literal style indicator (``|  # some comment``)
diff --git a/README.rst b/README.rst
index 8f540c3..0af8415 100644
--- a/README.rst
+++ b/README.rst
@@ -4,7 +4,7 @@ ruamel.yaml
 
 ``ruamel.yaml`` is a YAML 1.2 loader/dumper package for Python.
 
-:version:       0.15.49
+:version:       0.15.50
 :updated:       2018-08-05
 :documentation: http://yaml.readthedocs.io
 :repository:    https://bitbucket.org/ruamel/
@@ -54,6 +54,12 @@ ChangeLog
 
 .. should insert NEXT: at the beginning of line for next key (with empty line)
 
+0.15.50 (2018-08-05):
+  - Allow ``YAML()`` as a context manager for output, thereby making it much easier
+    to generate multi-documents in a stream. 
+  - Fix issue with incorrect type information for `load()` and `dump()` (reported 
+    by `Jimbo Jim <https://bitbucket.org/jimbo1qaz/>`__)
+
 0.15.49 (2018-08-05):
   - fix preservation of leading newlines in root level literal style scalar,
     and preserve comment after literal style indicator (``|  # some comment``)
diff --git a/__init__.py b/__init__.py
index ece2b5b..1e3bf42 100644
--- a/__init__.py
+++ b/__init__.py
@@ -7,8 +7,8 @@ if False:  # MYPY
 
 _package_data = dict(
     full_package_name='ruamel.yaml',
-    version_info=(0, 15, 50, 'dev'),
-    __version__='0.15.50.dev',
+    version_info=(0, 15, 50),
+    __version__='0.15.50',
     author='Anthon van der Neut',
     author_email='a.van.der.neut@ruamel.eu',
     description='ruamel.yaml is a YAML parser/emitter that supports roundtrip preservation of comments, seq/map flow style, and map key order',  # NOQA
diff --git a/_doc/_static/pypi.svg b/_doc/_static/pypi.svg
index 67703ce..a145534 100644
--- a/_doc/_static/pypi.svg
+++ b/_doc/_static/pypi.svg
@@ -1 +1 @@
-<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="86" height="20"><linearGradient id="b" x2="0" y2="100%"><stop offset="0" stop-color="#bbb" stop-opacity=".1"/><stop offset="1" stop-opacity=".1"/></linearGradient><clipPath id="a"><rect width="86" height="20" rx="3" fill="#fff"/></clipPath><g clip-path="url(#a)"><path fill="#555" d="M0 0h33v20H0z"/><path fill="#007ec6" d="M33 0h53v20H33z"/><path fill="url(#b)" d="M0 0h86v20H0z"/></g><g fill="#fff" text-anchor="middle" font-family="DejaVu Sans,Verdana,Geneva,sans-serif" font-size="110"> <text x="175" y="150" fill="#010101" fill-opacity=".3" transform="scale(.1)" textLength="230">pypi</text><text x="175" y="140" transform="scale(.1)" textLength="230">pypi</text><text x="585" y="150" fill="#010101" fill-opacity=".3" transform="scale(.1)" textLength="430">0.15.49</text><text x="585" y="140" transform="scale(.1)" textLength="430">0.15.49</text></g> </svg>
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="86" height="20"><linearGradient id="b" x2="0" y2="100%"><stop offset="0" stop-color="#bbb" stop-opacity=".1"/><stop offset="1" stop-opacity=".1"/></linearGradient><clipPath id="a"><rect width="86" height="20" rx="3" fill="#fff"/></clipPath><g clip-path="url(#a)"><path fill="#555" d="M0 0h33v20H0z"/><path fill="#007ec6" d="M33 0h53v20H33z"/><path fill="url(#b)" d="M0 0h86v20H0z"/></g><g fill="#fff" text-anchor="middle" font-family="DejaVu Sans,Verdana,Geneva,sans-serif" font-size="110"> <text x="175" y="150" fill="#010101" fill-opacity=".3" transform="scale(.1)" textLength="230">pypi</text><text x="175" y="140" transform="scale(.1)" textLength="230">pypi</text><text x="585" y="150" fill="#010101" fill-opacity=".3" transform="scale(.1)" textLength="430">0.15.50</text><text x="585" y="140" transform="scale(.1)" textLength="430">0.15.50</text></g> </svg>
diff --git a/_doc/api.ryd b/_doc/api.ryd
index a6c5afd..9e89b00 100644
--- a/_doc/api.ryd
+++ b/_doc/api.ryd
@@ -116,6 +116,62 @@ yaml.load(stream)
 In the old API this is a warning starting with 0.15.2 and an error in
 0.16.0.
 
+Dumping a multi-documents YAML stream
++++++++++++++++++++++++++++++++++++++
+
+The "normal" ``dump_all`` expected as first element a list of documents, or 
+something else the internals of the method can iterate over. To read
+and write a multi-document you would either make a ``list``::
+
+--- !code |
+   yaml = YAML()
+   data = list(yaml.load_all(in_path))
+   # do something on data[0], data[1], etc.
+   yaml.dump_all(data, out_path)
+--- |
+
+or create some function/object that would yield the ``data`` values.
+
+What you now can do is create ``YAML()`` as an context manager. This
+works for output (dumping) only, requires you to specify the output
+(file, buffer, ``Path``) at creation time, and doesn't support
+``transform`` (yet).
+
+::
+
+--- !code |
+    with YAML(output=sys.stdout) as yaml:
+            yaml.explicit_start = True
+            for data in yaml.load_all(Path(multi_document_filename)):
+                # do something on data
+                yaml.dump(data)
+--- |
+
+Within the context manager, you cannot use the ``dump()`` with a
+second (stream) argument, nor can you use ``dump_all()``. The
+``dump()`` within the context of the ``YAML()`` automatically creates
+ multi-document if called more than once.
+
+To combine multiple YAML documents from multiple files:
+
+::
+
+--- !code |
+    list_of_filenames = ['x.yaml', 'y.yaml', ]
+    with YAML(output=sys.stdout) as yaml:
+            yaml.explicit_start = True
+            for path in list_of_filename:
+                with open(path) as fp:
+                    yaml.dump(yaml.load(fp))
+--- |
+
+The output will be a valid, uniformly indented YAML file. Doing
+``cat {x,y}.yaml`` might result in a single document if there is not
+document start marker at the beginning of ``y.yaml``
+
+
+
+
 Dumping
 +++++++
 
diff --git a/_doc/basicuse.ryd b/_doc/basicuse.ryd
index c4a744d..9d2512d 100644
--- a/_doc/basicuse.ryd
+++ b/_doc/basicuse.ryd
@@ -38,7 +38,7 @@ enforce using the pure Python implementation (faster C libraries will be used
 when possible/available)
 
 Dumping works in the same way::
---- !python |
+--- !code |
 from ruamel.yaml import YAML
 
 yaml=YAML()
diff --git a/_test/test_contextmanager.py b/_test/test_contextmanager.py
index 85adf75..76d24aa 100644
--- a/_test/test_contextmanager.py
+++ b/_test/test_contextmanager.py
@@ -98,3 +98,15 @@ class TestContextManager:
     #     with YAML(input=multi_doc) as yaml:
     #         for idx, data in enumerate(yaml.load()):
     #             assert data == multi_doc_data[0]
+
+    def test_roundtrip(self, capsys):
+        from ruamel.yaml import YAML
+
+        with YAML(output=sys.stdout) as yaml:
+            yaml.explicit_start = True
+            for data in yaml.load_all(multi_doc):
+                yaml.dump(data)
+
+        out, err = capsys.readouterr()
+        print(err)
+        assert out == multi_doc
diff --git a/comments.py b/comments.py
index 32ce8ce..84fecbc 100644
--- a/comments.py
+++ b/comments.py
@@ -21,7 +21,7 @@ else:
     from collections.abc import MutableSet, Sized, Set
 
 if False:  # MYPY
-    from typing import Any, Dict, Optional, List, Union  # NOQA
+    from typing import Any, Dict, Optional, List, Union, Optional  # NOQA
 
 # fmt: off
 __all__ = ["CommentedSeq", "CommentedKeySeq",
@@ -127,7 +127,7 @@ class LineCol(object):
         # type: () -> None
         self.line = None
         self.col = None
-        self.data = None  # type: Union[None, Dict[Any, Any]]
+        self.data = None  # type: Optional[Dict[Any, Any]]
 
     def add_kv_line_col(self, key, data):
         # type: (Any, Any) -> None
diff --git a/compat.py b/compat.py
index a962103..3eb6464 100644
--- a/compat.py
+++ b/compat.py
@@ -9,7 +9,7 @@ import os
 import types
 
 if False:  # MYPY
-    from typing import Any, Dict, Optional, List, Union, BinaryIO, IO, Text, Tuple  # NOQA
+    from typing import Any, Dict, Optional, List, Union, BinaryIO, IO, Text, Tuple, Optional  # NOQA
 
 _DEFAULT_YAML_VERSION = (1, 2)
 
@@ -136,7 +136,7 @@ DBG_EVENT = 2
 DBG_NODE = 4
 
 
-_debug = None  # type: Union[None, int]
+_debug = None  # type: Optional[int]
 if 'RUAMELDEBUG' in os.environ:
     _debugx = os.environ.get('RUAMELDEBUG')
     if _debugx is None:
diff --git a/constructor.py b/constructor.py
index c36f01d..6de5181 100644
--- a/constructor.py
+++ b/constructor.py
@@ -29,7 +29,7 @@ from ruamel.yaml.timestamp import TimeStamp
 from ruamel.yaml.util import RegExp
 
 if False:  # MYPY
-    from typing import Any, Dict, List, Set, Generator, Union  # NOQA
+    from typing import Any, Dict, List, Set, Generator, Union, Optional  # NOQA
 
 
 __all__ = ['BaseConstructor', 'SafeConstructor', 'Constructor',
@@ -55,7 +55,7 @@ class BaseConstructor(object):
     yaml_multi_constructors = {}  # type: Dict[Any, Any]
 
     def __init__(self, preserve_quotes=None, loader=None):
-        # type: (Union[None, bool], Any) -> None
+        # type: (Optional[bool], Any) -> None
         self.loader = loader
         if self.loader is not None and getattr(self.loader, '_constructor', None) is None:
             self.loader._constructor = self
diff --git a/cyaml.py b/cyaml.py
index ed2c1da..3e013cb 100644
--- a/cyaml.py
+++ b/cyaml.py
@@ -9,7 +9,7 @@ from ruamel.yaml.representer import Representer, SafeRepresenter, BaseRepresente
 from ruamel.yaml.resolver import Resolver, BaseResolver
 
 if False:  # MYPY
-    from typing import Any, Union  # NOQA
+    from typing import Any, Union, Optional  # NOQA
     from ruamel.yaml.compat import StreamTextType, StreamType, VersionType  # NOQA
 
 __all__ = ['CBaseLoader', 'CSafeLoader', 'CLoader', 'CBaseDumper', 'CSafeDumper', 'CDumper']
@@ -21,7 +21,7 @@ __all__ = ['CBaseLoader', 'CSafeLoader', 'CLoader', 'CBaseDumper', 'CSafeDumper'
 
 class CBaseLoader(CParser, BaseConstructor, BaseResolver):  # type: ignore
     def __init__(self, stream, version=None, preserve_quotes=None):
-        # type: (StreamTextType, Union[None, VersionType], Union[None, bool]) -> None
+        # type: (StreamTextType, Optional[VersionType], Optional[bool]) -> None
         CParser.__init__(self, stream)
         self._parser = self._composer = self
         BaseConstructor.__init__(self, loader=self)
@@ -33,7 +33,7 @@ class CBaseLoader(CParser, BaseConstructor, BaseResolver):  # type: ignore
 
 class CSafeLoader(CParser, SafeConstructor, Resolver):  # type: ignore
     def __init__(self, stream, version=None, preserve_quotes=None):
-        # type: (StreamTextType, Union[None, VersionType], Union[None, bool]) -> None
+        # type: (StreamTextType, Optional[VersionType], Optional[bool]) -> None
         CParser.__init__(self, stream)
         self._parser = self._composer = self
         SafeConstructor.__init__(self, loader=self)
@@ -45,7 +45,7 @@ class CSafeLoader(CParser, SafeConstructor, Resolver):  # type: ignore
 
 class CLoader(CParser, Constructor, Resolver):  # type: ignore
     def __init__(self, stream, version=None, preserve_quotes=None):
-        # type: (StreamTextType, Union[None, VersionType], Union[None, bool]) -> None
+        # type: (StreamTextType, Optional[VersionType], Optional[bool]) -> None
         CParser.__init__(self, stream)
         self._parser = self._composer = self
         Constructor.__init__(self, loader=self)
@@ -75,7 +75,7 @@ class CBaseDumper(CEmitter, BaseRepresenter, BaseResolver):  # type: ignore
         top_level_colon_align=None,
         prefix_colon=None,
     ):
-        # type: (StreamType, Any, Any, Any, Union[None, bool], Union[None, int], Union[None, int], Union[None, bool], Any, Any, Union[None, bool], Union[None, bool], Any, Any, Any, Any, Any) -> None   # NOQA
+        # type: (StreamType, Any, Any, Any, Optional[bool], Optional[int], Optional[int], Optional[bool], Any, Any, Optional[bool], Optional[bool], Any, Any, Any, Any, Any) -> None   # NOQA
         CEmitter.__init__(
             self,
             stream,
@@ -120,7 +120,7 @@ class CSafeDumper(CEmitter, SafeRepresenter, Resolver):  # type: ignore
         top_level_colon_align=None,
         prefix_colon=None,
     ):
-        # type: (StreamType, Any, Any, Any, Union[None, bool], Union[None, int], Union[None, int], Union[None, bool], Any, Any, Union[None, bool], Union[None, bool], Any, Any, Any, Any, Any) -> None   # NOQA
+        # type: (StreamType, Any, Any, Any, Optional[bool], Optional[int], Optional[int], Optional[bool], Any, Any, Optional[bool], Optional[bool], Any, Any, Any, Any, Any) -> None   # NOQA
         self._emitter = self._serializer = self._representer = self
         CEmitter.__init__(
             self,
@@ -163,7 +163,7 @@ class CDumper(CEmitter, Representer, Resolver):  # type: ignore
         top_level_colon_align=None,
         prefix_colon=None,
     ):
-        # type: (StreamType, Any, Any, Any, Union[None, bool], Union[None, int], Union[None, int], Union[None, bool], Any, Any, Union[None, bool], Union[None, bool], Any, Any, Any, Any, Any) -> None   # NOQA
+        # type: (StreamType, Any, Any, Any, Optional[bool], Optional[int], Optional[int], Optional[bool], Any, Any, Optional[bool], Optional[bool], Any, Any, Any, Any, Any) -> None   # NOQA
         CEmitter.__init__(
             self,
             stream,
diff --git a/dumper.py b/dumper.py
index 5f23c45..5d99b4f 100644
--- a/dumper.py
+++ b/dumper.py
@@ -13,7 +13,7 @@ from ruamel.yaml.representer import (
 from ruamel.yaml.resolver import Resolver, BaseResolver, VersionedResolver
 
 if False:  # MYPY
-    from typing import Any, Dict, List, Union  # NOQA
+    from typing import Any, Dict, List, Union, Optional  # NOQA
     from ruamel.yaml.compat import StreamType, VersionType  # NOQA
 
 __all__ = ['BaseDumper', 'SafeDumper', 'Dumper', 'RoundTripDumper']
@@ -39,7 +39,7 @@ class BaseDumper(Emitter, Serializer, BaseRepresenter, BaseResolver):
         top_level_colon_align=None,
         prefix_colon=None,
     ):
-        # type: (Any, StreamType, Any, Any, Union[None, bool], Union[None, int], Union[None, int], Union[None, bool], Any, Any, Union[None, bool], Union[None, bool], Any, Any, Any, Any, Any) -> None   # NOQA
+        # type: (Any, StreamType, Any, Any, Optional[bool], Optional[int], Optional[int], Optional[bool], Any, Any, Optional[bool], Optional[bool], Any, Any, Any, Any, Any) -> None   # NOQA
         Emitter.__init__(
             self,
             stream,
@@ -89,7 +89,7 @@ class SafeDumper(Emitter, Serializer, SafeRepresenter, Resolver):
         top_level_colon_align=None,
         prefix_colon=None,
     ):
-        # type: (StreamType, Any, Any, Union[None, bool], Union[None, int], Union[None, int], Union[None, bool], Any, Any, Union[None, bool], Union[None, bool], Any, Any, Any, Any, Any) -> None  # NOQA
+        # type: (StreamType, Any, Any, Optional[bool], Optional[int], Optional[int], Optional[bool], Any, Any, Optional[bool], Optional[bool], Any, Any, Any, Any, Any) -> None  # NOQA
         Emitter.__init__(
             self,
             stream,
@@ -139,7 +139,7 @@ class Dumper(Emitter, Serializer, Representer, Resolver):
         top_level_colon_align=None,
         prefix_colon=None,
     ):
-        # type: (StreamType, Any, Any, Union[None, bool], Union[None, int], Union[None, int], Union[None, bool], Any, Any, Union[None, bool], Union[None, bool], Any, Any, Any, Any, Any) -> None   # NOQA
+        # type: (StreamType, Any, Any, Optional[bool], Optional[int], Optional[int], Optional[bool], Any, Any, Optional[bool], Optional[bool], Any, Any, Any, Any, Any) -> None   # NOQA
         Emitter.__init__(
             self,
             stream,
@@ -189,7 +189,7 @@ class RoundTripDumper(Emitter, Serializer, RoundTripRepresenter, VersionedResolv
         top_level_colon_align=None,
         prefix_colon=None,
     ):
-        # type: (StreamType, Any, Union[None, bool], Union[None, int], Union[None, int], Union[None, int], Union[None, bool], Any, Any, Union[None, bool], Union[None, bool], Any, Any, Any, Any, Any) -> None  # NOQA
+        # type: (StreamType, Any, Optional[bool], Optional[int], Optional[int], Optional[int], Optional[bool], Any, Any, Optional[bool], Optional[bool], Any, Any, Any, Any, Any) -> None  # NOQA
         Emitter.__init__(
             self,
             stream,
diff --git a/emitter.py b/emitter.py
index e45a0b1..7a81372 100644
--- a/emitter.py
+++ b/emitter.py
@@ -20,7 +20,7 @@ from ruamel.yaml.compat import utf8, text_type, PY2, nprint, dbg, DBG_EVENT, \
 # fmt: on
 
 if False:  # MYPY
-    from typing import Any, Dict, List, Union, Text, Tuple  # NOQA
+    from typing import Any, Dict, List, Union, Text, Tuple, Optional  # NOQA
     from ruamel.yaml.compat import StreamType  # NOQA
 
 __all__ = ['Emitter', 'EmitterError']
@@ -113,14 +113,14 @@ class Emitter(object):
         prefix_colon=None,
         dumper=None,
     ):
-        # type: (StreamType, Any, Union[None, int], Union[None, int], Union[None, bool], Any, Union[None, int], Union[None, bool], Any, Any) -> None  # NOQA
+        # type: (StreamType, Any, Optional[int], Optional[int], Optional[bool], Any, Optional[int], Optional[bool], Any, Any) -> None  # NOQA
         self.dumper = dumper
         if self.dumper is not None and getattr(self.dumper, '_emitter', None) is None:
             self.dumper._emitter = self
         self.stream = stream
 
         # Encoding can be overriden by STREAM-START.
-        self.encoding = None  # type: Union[None, Text]
+        self.encoding = None  # type: Optional[Text]
         self.allow_space_break = None
 
         # Emitter is a state machine with a stack of states to handle nested
@@ -134,7 +134,7 @@ class Emitter(object):
 
         # The current indentation level and the stack of previous indents.
         self.indents = Indents()
-        self.indent = None  # type: Union[None, int]
+        self.indent = None  # type: Optional[int]
 
         # Flow level.
         self.flow_level = 0
@@ -154,7 +154,7 @@ class Emitter(object):
         self.column = 0
         self.whitespace = True
         self.indention = True
-        self.no_newline = None  # type: Union[None, bool]  # set if directly after `- `
+        self.no_newline = None  # type: Optional[bool]  # set if directly after `- `
 
         # Whether the document requires an explicit document indicator
         self.open_ended = False
@@ -269,7 +269,7 @@ class Emitter(object):
         return len(self.events) < count + 1
 
     def increase_indent(self, flow=False, sequence=None, indentless=False):
-        # type: (bool, Union[None, bool], bool) -> None
+        # type: (bool, Optional[bool], bool) -> None
         self.indents.append(self.indent, sequence)
         if self.indent is None:  # top level
             if flow:
diff --git a/loader.py b/loader.py
index d8cbe31..979ec62 100644
--- a/loader.py
+++ b/loader.py
@@ -16,7 +16,7 @@ from ruamel.yaml.constructor import (
 from ruamel.yaml.resolver import VersionedResolver
 
 if False:  # MYPY
-    from typing import Any, Dict, List, Union  # NOQA
+    from typing import Any, Dict, List, Union, Optional  # NOQA
     from ruamel.yaml.compat import StreamTextType, VersionType  # NOQA
 
 __all__ = ['BaseLoader', 'SafeLoader', 'Loader', 'RoundTripLoader']
@@ -24,7 +24,7 @@ __all__ = ['BaseLoader', 'SafeLoader', 'Loader', 'RoundTripLoader']
 
 class BaseLoader(Reader, Scanner, Parser, Composer, BaseConstructor, VersionedResolver):
     def __init__(self, stream, version=None, preserve_quotes=None):
-        # type: (StreamTextType, Union[None, VersionType], Union[None, bool]) -> None
+        # type: (StreamTextType, Optional[VersionType], Optional[bool]) -> None
         Reader.__init__(self, stream, loader=self)
         Scanner.__init__(self, loader=self)
         Parser.__init__(self, loader=self)
@@ -35,7 +35,7 @@ class BaseLoader(Reader, Scanner, Parser, Composer, BaseConstructor, VersionedRe
 
 class SafeLoader(Reader, Scanner, Parser, Composer, SafeConstructor, VersionedResolver):
     def __init__(self, stream, version=None, preserve_quotes=None):
-        # type: (StreamTextType, Union[None, VersionType], Union[None, bool]) -> None
+        # type: (StreamTextType, Optional[VersionType], Optional[bool]) -> None
         Reader.__init__(self, stream, loader=self)
         Scanner.__init__(self, loader=self)
         Parser.__init__(self, loader=self)
@@ -46,7 +46,7 @@ class SafeLoader(Reader, Scanner, Parser, Composer, SafeConstructor, VersionedRe
 
 class Loader(Reader, Scanner, Parser, Composer, Constructor, VersionedResolver):
     def __init__(self, stream, version=None, preserve_quotes=None):
-        # type: (StreamTextType, Union[None, VersionType], Union[None, bool]) -> None
+        # type: (StreamTextType, Optional[VersionType], Optional[bool]) -> None
         Reader.__init__(self, stream, loader=self)
         Scanner.__init__(self, loader=self)
         Parser.__init__(self, loader=self)
@@ -64,7 +64,7 @@ class RoundTripLoader(
     VersionedResolver,
 ):
     def __init__(self, stream, version=None, preserve_quotes=None):
-        # type: (StreamTextType, Union[None, VersionType], Union[None, bool]) -> None
+        # type: (StreamTextType, Optional[VersionType], Optional[bool]) -> None
         # self.reader = Reader.__init__(self, stream)
         Reader.__init__(self, stream, loader=self)
         RoundTripScanner.__init__(self, loader=self)
diff --git a/main.py b/main.py
index a2a11f4..ce607bf 100644
--- a/main.py
+++ b/main.py
@@ -35,7 +35,7 @@ from ruamel.yaml.constructor import (
 from ruamel.yaml.loader import Loader as UnsafeLoader
 
 if False:  # MYPY
-    from typing import List, Set, Dict, Union, Any  # NOQA
+    from typing import List, Set, Dict, Union, Any, Callable  # NOQA
     from ruamel.yaml.compat import StreamType, StreamTextType, VersionType  # NOQA
 
     if PY3:
@@ -61,7 +61,7 @@ class YAML(object):
     def __init__(
         self, _kw=enforce, typ=None, pure=False, output=None, plug_ins=None  # input=None,
     ):
-        # type: (Any, Any, Any, Any) -> None
+        # type: (Any, Optional[Text], Any, Any, Any) -> None
         """
         _kw: not used, forces keyword arguments in 2.7 (in 3 you can do (*, safe_load=..)
         typ: 'rt'/None -> RoundTripLoader/RoundTripDumper,  (default)
@@ -83,7 +83,7 @@ class YAML(object):
 
         # self._input = input
         self._output = output
-        self._context_manager = False
+        self._context_manager = None  # type: Any
 
         self.plug_ins = []  # type: List[Any]
         for pu in ([] if plug_ins is None else plug_ins) + self.official_plug_ins():
@@ -394,7 +394,7 @@ class YAML(object):
 
                 class XLoader(self.Parser, self.Constructor, rslvr):  # type: ignore
                     def __init__(selfx, stream, version=None, preserve_quotes=None):
-                        # type: (StreamTextType, Union[None, VersionType], Union[None, bool]) -> None  # NOQA
+                        # type: (StreamTextType, Optional[VersionType], Optional[bool]) -> None  # NOQA
                         CParser.__init__(selfx, stream)
                         selfx._parser = selfx._composer = selfx
                         self.Constructor.__init__(selfx, loader=selfx)
@@ -411,7 +411,17 @@ class YAML(object):
         if self._context_manager:
             if not self._output:
                 raise TypeError('Missing output stream while dumping from context manager')
-            self._context_manager.dump(data, transform=transform)
+            if _kw is not enforce:
+                raise TypeError(
+                    '{}.dump() takes one positional argument but at least '
+                    'two were given ({!r})'.format(self.__class__.__name__, _kw)
+                )
+            if transform is not None:
+                raise TypeError(
+                    '{}.dump() in the context manager cannot have transform keyword '
+                    ''.format(self.__class__.__name__)
+                )
+            self._context_manager.dump(data)
         else:  # old style
             if stream is None:
                 raise TypeError('Need a stream argument when not dumping from context manager')
@@ -419,6 +429,23 @@ class YAML(object):
 
     def dump_all(self, documents, stream, _kw=enforce, transform=None):
         # type: (Any, Union[Path, StreamType], Any, Any) -> Any
+        if self._context_manager:
+            raise NotImplementedError
+        if _kw is not enforce:
+            raise TypeError(
+                '{}.dump(_all) takes two positional argument but at least '
+                'three were given ({!r})'.format(self.__class__.__name__, _kw)
+            )
+        self._output = stream
+        self._context_manager = YAMLContextManager(self, transform=transform)
+        for data in documents:
+            self._context_manager.dump(data)
+        self._context_manager.teardown_output()
+        self._output = None
+        self._context_manager = None
+
+    def Xdump_all(self, documents, stream, _kw=enforce, transform=None):
+        # type: (Any, Union[Path, StreamType], Any, Any) -> Any
         """
         Serialize a sequence of Python objects into a YAML stream.
         """
@@ -515,7 +542,7 @@ class YAML(object):
                 top_level_colon_align=None,
                 prefix_colon=None,
             ):
-                # type: (StreamType, Any, Any, Any, Union[None, bool], Union[None, int], Union[None, int], Union[None, bool], Any, Any, Union[None, bool], Union[None, bool], Any, Any, Any, Any, Any) -> None   # NOQA
+                # type: (StreamType, Any, Any, Any, Optional[bool], Optional[int], Optional[int], Optional[bool], Any, Any, Optional[bool], Optional[bool], Any, Any, Any, Any, Any) -> None   # NOQA
                 CEmitter.__init__(
                     selfx,
                     stream,
@@ -615,10 +642,12 @@ class YAML(object):
     # ### context manager
 
     def __enter__(self):
+        # type: () -> Any
         self._context_manager = YAMLContextManager(self)
         return self
 
     def __exit__(self, typ, value, traceback):
+        # type: (Any, Any, Any) -> None
         if typ:
             print('typ', typ)
         self._context_manager.teardown_output()
@@ -657,12 +686,13 @@ class YAML(object):
 
 
 class YAMLContextManager(object):
-    def __init__(self, yaml):
+    def __init__(self, yaml, transform=None):
+        # type: (Any, Optional[Callable]) -> None
         self._yaml = yaml
         self._output_inited = False
         self._output_path = None
         self._output = self._yaml._output
-        self._transform = False
+        self._transform = transform
 
         # self._input_inited = False
         # self._input = input
@@ -673,7 +703,7 @@ class YAMLContextManager(object):
         if not hasattr(self._output, 'write') and hasattr(self._output, 'open'):
             # pathlib.Path() instance, open with the same mode
             self._output_path = self._output
-            self._output = self._output_path.open('r')
+            self._output = self._output_path.open('w')
 
         # if not hasattr(self._stream, 'write') and hasattr(stream, 'open'):
         # if not hasattr(self._input, 'read') and hasattr(self._input, 'open'):
@@ -681,14 +711,15 @@ class YAMLContextManager(object):
         #    self._input_path = self._input
         #    self._input = self._input_path.open('r')
 
-        # if self._transform is not None:
-        #    self._fstream = self._stream
-        #    if self._yaml.encoding is None:
-        #        self._stream = StringIO()
-        #    else:
-        #        self._stream = BytesIO()
+        if self._transform is not None:
+            self._fstream = self._output
+            if self._yaml.encoding is None:
+                self._output = StringIO()
+            else:
+                self._output = BytesIO()
 
     def teardown_output(self):
+        # type: () -> None
         if self._output_inited:
             self._yaml.serializer.close()
         else:
@@ -702,21 +733,22 @@ class YAMLContextManager(object):
             delattr(self._yaml, '_serializer')
             delattr(self._yaml, '_emitter')
         except AttributeError:
-            if not typ:
-                raise
+            raise
         if self._transform:
-            val = self._stream.getvalue()  # type: ignore
+            val = self._output.getvalue()
             if self._yaml.encoding:
                 val = val.decode(self._yaml.encoding)
             if self._fstream is None:
                 self._transform(val)
             else:
                 self._fstream.write(self._transform(val))
-                self._fstream.close()
+                self._fstream.flush()
+                self._output = self._fstream  # maybe not necessary
         if self._output_path is not None:
             self._output.close()
 
-    def init_output(self, data):
+    def init_output(self, first_data):
+        # type: (Any) -> None
         if self._yaml.top_level_colon_align is True:
             tlca = max([len(str(x)) for x in first_data])  # type: Any
         else:
@@ -725,7 +757,8 @@ class YAMLContextManager(object):
         self._yaml.serializer.open()
         self._output_inited = True
 
-    def dump(self, data, transform=None):
+    def dump(self, data):
+        # type: (Any) -> None
         if not self._output_inited:
             self.init_output(data)
         try:
@@ -853,7 +886,7 @@ def compose_all(stream, Loader=Loader):
 
 
 def load(stream, Loader=None, version=None, preserve_quotes=None):
-    # type: (StreamTextType, Any, Union[None, VersionType], Any) -> Any
+    # type: (StreamTextType, Any, Optional[VersionType], Any) -> Any
     """
     Parse the first YAML document in a stream
     and produce the corresponding Python object.
@@ -869,7 +902,7 @@ def load(stream, Loader=None, version=None, preserve_quotes=None):
 
 
 def load_all(stream, Loader=None, version=None, preserve_quotes=None):
-    # type: (Union[None, StreamTextType], Any, Union[None, VersionType], Union[None, bool]) -> Any  # NOQA
+    # type: (Optional[StreamTextType], Any, Optional[VersionType], Optional[bool]) -> Any  # NOQA
     """
     Parse all YAML documents in a stream
     and produce corresponding Python objects.
@@ -886,7 +919,7 @@ def load_all(stream, Loader=None, version=None, preserve_quotes=None):
 
 
 def safe_load(stream, version=None):
-    # type: (StreamTextType, Union[None, VersionType]) -> Any
+    # type: (StreamTextType, Optional[VersionType]) -> Any
     """
     Parse the first YAML document in a stream
     and produce the corresponding Python object.
@@ -896,7 +929,7 @@ def safe_load(stream, version=None):
 
 
 def safe_load_all(stream, version=None):
-    # type: (StreamTextType, Union[None, VersionType]) -> Any
+    # type: (StreamTextType, Optional[VersionType]) -> Any
     """
     Parse all YAML documents in a stream
     and produce corresponding Python objects.
@@ -906,7 +939,7 @@ def safe_load_all(stream, version=None):
 
 
 def round_trip_load(stream, version=None, preserve_quotes=None):
-    # type: (StreamTextType, Union[None, VersionType], Union[None, bool]) -> Any
+    # type: (StreamTextType, Optional[VersionType], Optional[bool]) -> Any
     """
     Parse the first YAML document in a stream
     and produce the corresponding Python object.
@@ -916,7 +949,7 @@ def round_trip_load(stream, version=None, preserve_quotes=None):
 
 
 def round_trip_load_all(stream, version=None, preserve_quotes=None):
-    # type: (StreamTextType, Union[None, VersionType], Union[None, bool]) -> Any
+    # type: (StreamTextType, Optional[VersionType], Optional[bool]) -> Any
     """
     Parse all YAML documents in a stream
     and produce corresponding Python objects.
@@ -935,7 +968,7 @@ def emit(
     allow_unicode=None,
     line_break=None,
 ):
-    # type: (Any, Union[None, StreamType], Any, Union[None, bool], Union[int, None], Union[None, int], Union[None, bool], Any) -> Any  # NOQA
+    # type: (Any, Optional[StreamType], Any, Optional[bool], Union[int, None], Optional[int], Optional[bool], Any) -> Any  # NOQA
     """
     Emit YAML parsing events into a stream.
     If stream is None, return the produced string instead.
@@ -983,7 +1016,7 @@ def serialize_all(
     version=None,
     tags=None,
 ):
-    # type: (Any, Union[None, StreamType], Any, Any, Union[None, int], Union[None, int], Union[None, bool], Any, Any, Union[None, bool], Union[None, bool], Union[None, VersionType], Any) -> Any # NOQA
+    # type: (Any, Optional[StreamType], Any, Any, Optional[int], Optional[int], Optional[bool], Any, Any, Optional[bool], Optional[bool], Optional[VersionType], Any) -> Any # NOQA
     """
     Serialize a sequence of representation trees into a YAML stream.
     If stream is None, return the produced string instead.
@@ -1024,7 +1057,7 @@ def serialize_all(
 
 
 def serialize(node, stream=None, Dumper=Dumper, **kwds):
-    # type: (Any, Union[None, StreamType], Any, Any) -> Any
+    # type: (Any, Optional[StreamType], Any, Any) -> Any
     """
     Serialize a representation tree into a YAML stream.
     If stream is None, return the produced string instead.
@@ -1052,7 +1085,7 @@ def dump_all(
     top_level_colon_align=None,
     prefix_colon=None,
 ):
-    # type: (Any, Union[None, StreamType], Any, Any, Any, Union[None, bool], Union[None, int], Union[None, int], Union[None, bool], Any, Any, Union[None, bool], Union[None, bool], Any, Any, Any, Any, Any) -> Union[None, str]   # NOQA
+    # type: (Any, Optional[StreamType], Any, Any, Any, Optional[bool], Optional[int], Optional[int], Optional[bool], Any, Any, Optional[bool], Optional[bool], Any, Any, Any, Any, Any) -> Optional[str]   # NOQA
     """
     Serialize a sequence of Python objects into a YAML stream.
     If stream is None, return the produced string instead.
@@ -1122,7 +1155,7 @@ def dump(
     tags=None,
     block_seq_indent=None,
 ):
-    # type: (Any, Union[None, StreamType], Any, Any, Any, Union[None, bool], Union[None, int], Union[None, int], Union[None, bool], Any, Any, Union[None, bool], Union[None, bool], Union[None, VersionType], Any, Any) -> Union[None, str]   # NOQA
+    # type: (Any, Optional[StreamType], Any, Any, Any, Optional[bool], Optional[int], Optional[int], Optional[bool], Any, Any, Optional[bool], Optional[bool], Optional[VersionType], Any, Any) -> Optional[str]   # NOQA
     """
     Serialize a Python object into a YAML stream.
     If stream is None, return the produced string instead.
@@ -1151,7 +1184,7 @@ def dump(
 
 
 def safe_dump_all(documents, stream=None, **kwds):
-    # type: (Any, Union[None, StreamType], Any) -> Union[None, str]
+    # type: (Any, Optional[StreamType], Any) -> Optional[str]
     """
     Serialize a sequence of Python objects into a YAML stream.
     Produce only basic YAML tags.
@@ -1161,7 +1194,7 @@ def safe_dump_all(documents, stream=None, **kwds):
 
 
 def safe_dump(data, stream=None, **kwds):
-    # type: (Any, Union[None, StreamType], Any) -> Union[None, str]
+    # type: (Any, Optional[StreamType], Any) -> Optional[str]
     """
     Serialize a Python object into a YAML stream.
     Produce only basic YAML tags.
@@ -1190,7 +1223,7 @@ def round_trip_dump(
     top_level_colon_align=None,
     prefix_colon=None,
 ):
-    # type: (Any, Union[None, StreamType], Any, Any, Any, Union[None, bool], Union[None, int], Union[None, int], Union[None, bool], Any, Any, Union[None, bool], Union[None, bool], Union[None, VersionType], Any, Any, Any, Any) -> Union[None, str]   # NOQA
+    # type: (Any, Optional[StreamType], Any, Any, Any, Optional[bool], Optional[int], Optional[int], Optional[bool], Any, Any, Optional[bool], Optional[bool], Optional[VersionType], Any, Any, Any, Any) -> Optional[str]   # NOQA
     allow_unicode = True if allow_unicode is None else allow_unicode
     return dump_all(
         [data],
diff --git a/reader.py b/reader.py
index 4d0ddb4..dc9a036 100644
--- a/reader.py
+++ b/reader.py
@@ -28,7 +28,7 @@ from ruamel.yaml.compat import text_type, binary_type, PY3, UNICODE_SIZE
 from ruamel.yaml.util import RegExp
 
 if False:  # MYPY
-    from typing import Any, Dict, Optional, List, Union, Text, Tuple  # NOQA
+    from typing import Any, Dict, Optional, List, Union, Text, Tuple, Optional  # NOQA
     from ruamel.yaml.compat import StreamTextType  # NOQA
 
 __all__ = ['Reader', 'ReaderError']
@@ -93,7 +93,7 @@ class Reader(object):
         self.pointer = 0
         self.raw_buffer = None  # type: Any
         self.raw_decode = None
-        self.encoding = None  # type: Union[None, Text]
+        self.encoding = None  # type: Optional[Text]
         self.index = 0
         self.line = 0
         self.column = 0
@@ -202,7 +202,7 @@ class Reader(object):
 
     @classmethod
     def _get_non_printable_ascii(cls, data):  # type: ignore
-        # type: (Text, bytes) -> Union[None, Tuple[int, Text]]
+        # type: (Text, bytes) -> Optional[Tuple[int, Text]]
         ascii_bytes = data.encode('ascii')
         non_printables = ascii_bytes.translate(None, cls._printable_ascii)  # type: ignore
         if not non_printables:
@@ -212,7 +212,7 @@ class Reader(object):
 
     @classmethod
     def _get_non_printable_regex(cls, data):
-        # type: (Text) -> Union[None, Tuple[int, Text]]
+        # type: (Text) -> Optional[Tuple[int, Text]]
         match = cls.NON_PRINTABLE.search(data)
         if not bool(match):
             return None
@@ -220,7 +220,7 @@ class Reader(object):
 
     @classmethod
     def _get_non_printable(cls, data):
-        # type: (Text) -> Union[None, Tuple[int, Text]]
+        # type: (Text) -> Optional[Tuple[int, Text]]
         try:
             return cls._get_non_printable_ascii(data)  # type: ignore
         except UnicodeEncodeError:
@@ -276,7 +276,7 @@ class Reader(object):
                 break
 
     def update_raw(self, size=None):
-        # type: (Union[None, int]) -> None
+        # type: (Optional[int]) -> None
         if size is None:
             size = 4096 if PY3 else 1024
         data = self.stream.read(size)
diff --git a/representer.py b/representer.py
index 07b2535..a659977 100644
--- a/representer.py
+++ b/representer.py
@@ -26,7 +26,7 @@ else:
     import copy_reg as copyreg  # type: ignore
 
 if False:  # MYPY
-    from typing import Dict, List, Any, Union, Text  # NOQA
+    from typing import Dict, List, Any, Union, Text, Optional  # NOQA
 
 # fmt: off
 __all__ = ['BaseRepresenter', 'SafeRepresenter', 'Representer',
@@ -62,7 +62,7 @@ class BaseRepresenter(object):
         self.default_flow_style = default_flow_style
         self.represented_objects = {}  # type: Dict[Any, Any]
         self.object_keeper = []  # type: List[Any]
-        self.alias_key = None  # type: Union[None, int]
+        self.alias_key = None  # type: Optional[int]
 
     @property
     def serializer(self):
diff --git a/resolver.py b/resolver.py
index 6b8c56e..34e3d1e 100644
--- a/resolver.py
+++ b/resolver.py
@@ -5,7 +5,7 @@ from __future__ import absolute_import
 import re
 
 if False:  # MYPY
-    from typing import Any, Dict, List, Union, Text  # NOQA
+    from typing import Any, Dict, List, Union, Text, Optional  # NOQA
     from ruamel.yaml.compat import VersionType  # NOQA
 
 from ruamel.yaml.compat import string_types, _DEFAULT_YAML_VERSION  # NOQA
@@ -377,7 +377,7 @@ class VersionedResolver(BaseResolver):
     """
 
     def __init__(self, version=None, loader=None):
-        # type: (Union[None, VersionType], Any) -> None
+        # type: (Optional[VersionType], Any) -> None
         BaseResolver.__init__(self, loader)
         self._loader_version = self.get_loader_version(version)
         self._version_implicit_resolver = {}  # type: Dict[Any, Any]
@@ -391,7 +391,7 @@ class VersionedResolver(BaseResolver):
             impl_resolver.setdefault(ch, []).append((tag, regexp))
 
     def get_loader_version(self, version):
-        # type: (Union[VersionType, None]) -> Any
+        # type: (Optional[VersionType]) -> Any
         if version is None or isinstance(version, tuple):
             return version
         if isinstance(version, list):
diff --git a/serializer.py b/serializer.py
index b2b26bf..fa4ae62 100644
--- a/serializer.py
+++ b/serializer.py
@@ -21,7 +21,7 @@ from ruamel.yaml.events import (
 from ruamel.yaml.nodes import MappingNode, ScalarNode, SequenceNode
 
 if False:  # MYPY
-    from typing import Any, Dict, Union, Text  # NOQA
+    from typing import Any, Dict, Union, Text, Optional  # NOQA
     from ruamel.yaml.compat import VersionType  # NOQA
 
 __all__ = ['Serializer', 'SerializerError']
@@ -46,7 +46,7 @@ class Serializer(object):
         tags=None,
         dumper=None,
     ):
-        # type: (Any, Union[None, bool], Union[None, bool], Union[None, VersionType], Any, Any) -> None  # NOQA
+        # type: (Any, Optional[bool], Optional[bool], Optional[VersionType], Any, Any) -> None  # NOQA
         self.dumper = dumper
         if self.dumper is not None:
             self.dumper._serializer = self
@@ -61,7 +61,7 @@ class Serializer(object):
         self.serialized_nodes = {}  # type: Dict[Any, Any]
         self.anchors = {}  # type: Dict[Any, Any]
         self.last_anchor_id = 0
-        self.closed = None  # type: Union[None, bool]
+        self.closed = None  # type: Optional[bool]
         self._templated_id = None
 
     @property