fix for issue 3840.17.5

aliased scalars in !!set would not round trip with ?

15 files changed, 164 insertions, 93 deletions

diff --git a/CHANGES b/CHANGES
index ff47c47..8b5c36f 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,7 @@
+[0, 17, 5]: 2021-05-30
+  - fix for issue 384 !!set with aliased entry resulting in broken YAML on rt
+    reported by  `William Kimball <https://sourceforge.net/u/william303/>`__)
+
 [0, 17, 4]: 2021-04-07
   - prevent (empty) comments from throwing assertion error (issue 351 
     reported by  `William Kimball <https://sourceforge.net/u/william303/>`__)
diff --git a/README.rst b/README.rst
index cdf3498..2d83774 100644
--- a/README.rst
+++ b/README.rst
@@ -4,8 +4,8 @@ ruamel.yaml
 
 ``ruamel.yaml`` is a YAML 1.2 loader/dumper package for Python.
 
-:version:       0.17.4
-:updated:       2021-04-07
+:version:       0.17.5
+:updated:       2021-05-30
 :documentation: http://yaml.readthedocs.io
 :repository:    https://sourceforge.net/projects/ruamel-yaml/
 :pypi:          https://pypi.org/project/ruamel.yaml/
@@ -65,6 +65,10 @@ ChangeLog
 
 .. should insert NEXT: at the beginning of line for next key (with empty line)
 
+0.17.5 (2021-05-30):
+  - fix for issue 384 !!set with aliased entry resulting in broken YAML on rt
+    reported by  `William Kimball <https://sourceforge.net/u/william303/>`__)
+
 0.17.4 (2021-04-07):
   - prevent (empty) comments from throwing assertion error (issue 351 
     reported by  `William Kimball <https://sourceforge.net/u/william303/>`__)
diff --git a/__init__.py b/__init__.py
index ee2b544..ef4c8b4 100644
--- a/__init__.py
+++ b/__init__.py
@@ -5,8 +5,8 @@ if False:  # MYPY
 
 _package_data = dict(
     full_package_name='ruamel.yaml',
-    version_info=(0, 17, 4),
-    __version__='0.17.4',
+    version_info=(0, 17, 5),
+    __version__='0.17.5',
     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 d88372e..820debd 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">0.17.4</text><text x="585" y="140" transform="scale(.1)" textLength="430">0.17.4</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">0.17.5</text><text x="585" y="140" transform="scale(.1)" textLength="430">0.17.5</text></g> </svg>
diff --git a/comments.py b/comments.py
index f49c183..d429fe1 100644
--- a/comments.py
+++ b/comments.py
@@ -11,7 +11,7 @@ import copy
 
 
 from ruamel.yaml.compat import ordereddict  # type: ignore
-from ruamel.yaml.compat import MutableSliceableSequence, _F, nprintf
+from ruamel.yaml.compat import MutableSliceableSequence, _F, nprintf  # NOQA
 from ruamel.yaml.scalarstring import ScalarString
 from ruamel.yaml.anchor import Anchor
 
@@ -24,22 +24,24 @@ if False:  # MYPY
 __all__ = ['CommentedSeq', 'CommentedKeySeq',
            'CommentedMap', 'CommentedOrderedMap',
            'CommentedSet', 'comment_attrib', 'merge_attrib',
-           'C_POST', 'C_PRE', 'C_SPLIT_ON_FIRST_BLANK', 'C_BLANK_LINE_PRESERVE_SPACE', 
+           'C_POST', 'C_PRE', 'C_SPLIT_ON_FIRST_BLANK', 'C_BLANK_LINE_PRESERVE_SPACE',
            ]
 # fmt: on
 
 # splitting of comments by the scanner
 # an EOLC (End-Of-Line Comment) is preceded by some token
-# an FLC (Full Line Comment) is a comment not preceded by a token, i.e. # is first non-blank on line
+# an FLC (Full Line Comment) is a comment not preceded by a token, i.e. # is
+#   the first non-blank on line
 # a BL is a blank line i.e. empty or spaces/tabs only
 # bits 0 and 1 are combined, you can choose only one
 C_POST = 0b00
-C_PRE =  0b01
-C_SPLIT_ON_FIRST_BLANK = 0b10   # as C_POST, but if blank line then C_PRE all lines before first
-                                # blank goes to POST even if no following real FLC (first blank -> first of post)
+C_PRE = 0b01
+C_SPLIT_ON_FIRST_BLANK = 0b10  # as C_POST, but if blank line then C_PRE all lines before
+# first blank goes to POST even if no following real FLC
+# (first blank -> first of post)
 # 0b11 -> reserved for future use
-C_BLANK_LINE_PRESERVE_SPACE = 0b100 
-# C_EOL_PRESERVE_SPACE2 = 0b1000 
+C_BLANK_LINE_PRESERVE_SPACE = 0b100
+# C_EOL_PRESERVE_SPACE2 = 0b1000
 
 
 class IDX:
@@ -55,14 +57,15 @@ class IDX:
     def __str__(self):
         return str(self._idx)
 
+
 cidx = IDX()
 
 # more or less in order of subjective expected likelyhood
 # the _POST and _PRE ones are lists themselves
 C_VALUE_EOL = C_ELEM_EOL = cidx()
 C_KEY_EOL = cidx()
-C_KEY_PRE = C_ELEM_PRE = cidx()   # not this is not value
-C_VALUE_POST = C_ELEM_POST = cidx()   # not this is not value
+C_KEY_PRE = C_ELEM_PRE = cidx()  # not this is not value
+C_VALUE_POST = C_ELEM_POST = cidx()  # not this is not value
 C_VALUE_PRE = cidx()
 C_KEY_POST = cidx()
 C_TAG_EOL = cidx()
@@ -140,7 +143,6 @@ class Comment:
             it = '\n    ' + it + '  '
         return 'Comment(\n  pre={},\n  items={{{}}}{})'.format(self.pre, it, end)
 
-
     @property
     def items(self):
         # type: () -> Any
diff --git a/compat.py b/compat.py
index 10ebc23..e88b433 100644
--- a/compat.py
+++ b/compat.py
@@ -166,6 +166,7 @@ class Nprint:
         out = sys.stdout if self._file_name is None else open(self._file_name, mode)
         return out
 
+
 nprint = Nprint()
 nprintf = Nprint('/var/tmp/ruamel.yaml.log')
 
diff --git a/constructor.py b/constructor.py
index 199129e..0a5db9b 100644
--- a/constructor.py
+++ b/constructor.py
@@ -1323,8 +1323,9 @@ class RoundTripConstructor(SafeConstructor):
             if node.comment:
                 seqtyp._yaml_add_comment(node.comment[:2])
                 if len(node.comment) > 2:
-                    # this happens e.g. if you have a sequence element that is a flow-style mapping
-                    # and that has no EOL comment but a following commentline or empty line
+                    # this happens e.g. if you have a sequence element that is a flow-style
+                    # mapping and that has no EOL comment but a following commentline or
+                    # empty line
                     seqtyp.yaml_end_comment_extend(node.comment[2], clear=True)
         else:
             # NEWCMNT
diff --git a/emitter.py b/emitter.py
index afbffc4..635bb22 100644
--- a/emitter.py
+++ b/emitter.py
@@ -13,7 +13,7 @@ from ruamel.yaml.events import *  # NOQA
 
 # fmt: off
 from ruamel.yaml.compat import _F, nprint, dbg, DBG_EVENT, \
-    check_anchorname_char, nprintf
+    check_anchorname_char, nprintf  # NOQA
 # fmt: on
 
 if False:  # MYPY
@@ -695,7 +695,8 @@ class Emitter:
                         pass
                 self.states.append(self.expect_block_mapping_simple_value)
                 self.expect_node(mapping=True, simple_key=True)
-                if isinstance(self.event, AliasEvent):
+                # test on style for alias in !!set
+                if isinstance(self.event, AliasEvent) and not self.event.style == '?':
                     self.stream.write(' ')
             else:
                 self.write_indicator('?', True, indention=True)
@@ -1562,7 +1563,7 @@ class Emitter:
     def write_literal(self, text, comment=None):
         # type: (Any, Any) -> None
         hints, _indent, _indicator = self.determine_block_hints(text)
-        #if comment is not None:
+        # if comment is not None:
         #    try:
         #        hints += comment[1][0]
         #    except (TypeError, IndexError) as e:
@@ -1570,12 +1571,12 @@ class Emitter:
         if not isinstance(comment, str):
             comment = ''
         self.write_indicator('|' + hints + comment, True)
-        #try:
+        # try:
         #    nprintf('selfev', comment)
         #    cmx = comment[1][0]
         #    if cmx:
         #        self.stream.write(cmx)
-        #except (TypeError, IndexError) as e:
+        # except (TypeError, IndexError) as e:
         #    pass
         if _indicator == '+':
             self.open_ended = True
diff --git a/events.py b/events.py
index e0c7f68..7a02a29 100644
--- a/events.py
+++ b/events.py
@@ -32,7 +32,7 @@ class Event:
         if True:
             arguments = []
             if hasattr(self, 'value'):
-                arguments.append(repr(getattr(self, 'value')))
+                arguments.append(repr(self.value))
             for key in ['anchor', 'tag', 'implicit', 'flow_style', 'style']:
                 v = getattr(self, key, None)
                 if v is not None:
@@ -40,8 +40,14 @@ class Event:
             if self.comment not in [None, CommentCheck]:
                 arguments.append('comment={!r}'.format(self.comment))
             if SHOW_LINES:
-                arguments.append('({}:{}/{}:{})'.format(self.start_mark.line, self.start_mark.column,
-                                                    self.end_mark.line, self.end_mark.column))
+                arguments.append(
+                    '({}:{}/{}:{})'.format(
+                        self.start_mark.line,
+                        self.start_mark.column,
+                        self.end_mark.line,
+                        self.end_mark.column,
+                    )
+                )
             arguments = ', '.join(arguments)
         else:
             attributes = [
@@ -50,7 +56,7 @@ class Event:
                 if hasattr(self, key)
             ]
             arguments = ', '.join(
-                [_F('{key!s}={attr!r}', key=key, attr=getattr(self, key)) for key in attributes]
+                [_F('{k!s}={attr!r}', k=key, attr=getattr(self, key)) for key in attributes]
             )
             if self.comment not in [None, CommentCheck]:
                 arguments += ', comment={!r}'.format(self.comment)
@@ -141,7 +147,11 @@ class DocumentEndEvent(Event):
 
 
 class AliasEvent(NodeEvent):
-    __slots__ = ()
+    __slots__ = 'style'
+
+    def __init__(self, anchor, start_mark=None, end_mark=None, style=None, comment=None):
+        NodeEvent.__init__(self, anchor, start_mark, end_mark, comment)
+        self.style = style
 
 
 class ScalarEvent(NodeEvent):
diff --git a/main.py b/main.py
index e19f28c..397f5dd 100644
--- a/main.py
+++ b/main.py
@@ -16,7 +16,7 @@ from ruamel.yaml.nodes import *  # NOQA
 
 from ruamel.yaml.loader import BaseLoader, SafeLoader, Loader, RoundTripLoader  # NOQA
 from ruamel.yaml.dumper import BaseDumper, SafeDumper, Dumper, RoundTripDumper  # NOQA
-from ruamel.yaml.compat import StringIO, BytesIO, with_metaclass, nprint, nprintf
+from ruamel.yaml.compat import StringIO, BytesIO, with_metaclass, nprint, nprintf  # NOQA
 from ruamel.yaml.resolver import VersionedResolver, Resolver  # NOQA
 from ruamel.yaml.representer import (
     BaseRepresenter,
diff --git a/parser.py b/parser.py
index 8e2f54e..db225a1 100644
--- a/parser.py
+++ b/parser.py
@@ -92,6 +92,7 @@ def xprintf(*args, **kw):
     return nprintf(*args, **kw)
     pass
 
+
 class ParserError(MarkedYAMLError):
     pass
 
@@ -834,8 +835,8 @@ class RoundTripParser(Parser):
 
 class RoundTripParserSC(RoundTripParser):
     """roundtrip is a safe loader, that wants to see the unmangled tag"""
-
-    # some of the differences are based on the superclass testing if self.loader.comment_handling is not None
+    # some of the differences are based on the superclass testing
+    # if self.loader.comment_handling is not None
 
     def move_token_comment(self, token, nt=None, empty=False):
         token.move_new_comment(self.scanner.peek_token() if nt is None else nt, empty=empty)
@@ -846,11 +847,11 @@ class RoundTripParserSC(RoundTripParser):
             return None
         if not comment[0]:
             return None
-        if  comment[0][0] != line + 1:
+        if comment[0][0] != line + 1:
             nprintf('>>>dcxxx', comment, line, typ)
         assert comment[0][0] == line + 1
-        #if comment[0] - line > 1:
-        #    return
+        # if comment[0] - line > 1:
+        #     return
         typ = self.loader.comment_handling & 0b11
         # nprintf('>>>dca', comment, line, typ)
         if typ == C_POST:
@@ -860,7 +861,7 @@ class RoundTripParserSC(RoundTripParser):
             comment[0] = None
             return c
         # nprintf('>>>dcb', comment[0])
-        for idx, cmntidx in enumerate(comment[0]):
+        for cmntidx in comment[0]:
             # nprintf('>>>dcb', cmntidx)
             if isinstance(self.scanner.comments[cmntidx], BlankLineComment):
                 break
@@ -874,5 +875,3 @@ class RoundTripParserSC(RoundTripParser):
             comment[0] = comment[0][idx:]
             return c
         raise NotImplementedError  # reserved
-
-
diff --git a/representer.py b/representer.py
index f3e3e43..4b78c65 100644
--- a/representer.py
+++ b/representer.py
@@ -837,13 +837,17 @@ class RoundTripRepresenter(SafeRepresenter):
                 for ct in node.comment[1]:
                     ct.reset()
             item_comments = comment.items
-            for v in item_comments.values():
-                if v and v[1]:
-                    for ct in v[1]:
-                        ct.reset()
-            try:
-                node.comment.append(comment.end)
-            except AttributeError:
+            if self.dumper.comment_handling is None:
+                for v in item_comments.values():
+                    if v and v[1]:
+                        for ct in v[1]:
+                            ct.reset()
+                try:
+                    node.comment.append(comment.end)
+                except AttributeError:
+                    pass
+            else:
+                # NEWCMNT
                 pass
         except AttributeError:
             item_comments = {}
diff --git a/scanner.py b/scanner.py
index f9e6052..0a516f7 100644
--- a/scanner.py
+++ b/scanner.py
@@ -29,7 +29,7 @@
 #
 
 import inspect
-from ruamel.yaml.error import MarkedYAMLError, CommentMark
+from ruamel.yaml.error import MarkedYAMLError, CommentMark  # NOQA
 from ruamel.yaml.tokens import *  # NOQA
 from ruamel.yaml.compat import _F, check_anchorname_char, nprint, nprintf  # NOQA
 
@@ -44,6 +44,7 @@ _THE_END = '\n\0\r\x85\u2028\u2029'
 _THE_END_SPACE_TAB = ' \n\0\t\r\x85\u2028\u2029'
 _SPACE_TAB = ' \t'
 
+
 def xprintf(*args, **kw):
     return nprintf(*args, **kw)
     pass
@@ -1606,7 +1607,8 @@ class Scanner:
                 break
 
         token = ScalarToken("".join(chunks), True, start_mark, end_mark)
-        # getattr provides True so C type loader, which cannot handle comment, will not make CommentToken
+        # getattr provides True so C type loader, which cannot handle comment,
+        # will not make CommentToken
         if self.loader is not None:
             comment_handler = getattr(self.loader, 'comment_handling', False)
             if comment_handler is None:
@@ -2002,16 +2004,17 @@ class RoundTripScanner(Scanner):
         return Scanner.scan_block_scalar(self, style, rt=rt)
 
 
-# commenthandling 2021, differentiatiation not needed 
+# commenthandling 2021, differentiatiation not needed
 
 VALUECMNT = 0
 KEYCMNT = 0  # 1
-#TAGCMNT = 2
-#ANCHORCMNT = 3
+# TAGCMNT = 2
+# ANCHORCMNT = 3
 
 
 class CommentBase:
     __slots__ = ('value', 'line', 'column', 'used', 'function', 'fline', 'ufun', 'uline')
+
     def __init__(self, value, line, column):
         self.value = value
         self.line = line
@@ -2039,9 +2042,18 @@ class CommentBase:
         return _F('{value!r}', value=self.value)
 
     def info(self):
-        return _F('{name}{used} {line:2}:{column:<2} "{value:40s} {function}:{fline} {ufun}:{uline}',
-                  name=self.name, line=self.line, column=self.column, value=self.value + '"', used=self.used,
-                  function=self.function, fline=self.fline, ufun=self.ufun, uline=self.uline)
+        return _F(
+            '{name}{used} {line:2}:{column:<2} "{value:40s} {function}:{fline} {ufun}:{uline}',
+            name=self.name,
+            line=self.line,
+            column=self.column,
+            value=self.value + '"',
+            used=self.used,
+            function=self.function,
+            fline=self.fline,
+            ufun=self.ufun,
+            uline=self.uline,
+        )
 
 
 class EOLComment(CommentBase):
@@ -2071,7 +2083,7 @@ class ScannedComments:
         self.unused = []
 
     def add_eol_comment(self, comment, column, line):
-        info = inspect.getframeinfo(inspect.stack()[1][0])
+        # info = inspect.getframeinfo(inspect.stack()[1][0])
         if comment.count('\n') == 1:
             assert comment[-1] == '\n'
         else:
@@ -2081,7 +2093,7 @@ class ScannedComments:
         return retval
 
     def add_blank_line(self, comment, column, line):
-        info = inspect.getframeinfo(inspect.stack()[1][0])
+        # info = inspect.getframeinfo(inspect.stack()[1][0])
         assert comment.count('\n') == 1 and comment[-1] == '\n'
         assert line not in self.comments
         self.comments[line] = retval = BlankLineComment(comment[:-1], line, column)
@@ -2089,9 +2101,9 @@ class ScannedComments:
         return retval
 
     def add_full_line_comment(self, comment, column, line):
-        info = inspect.getframeinfo(inspect.stack()[1][0])
+        # info = inspect.getframeinfo(inspect.stack()[1][0])
         assert comment.count('\n') == 1 and comment[-1] == '\n'
-        #if comment.startswith('# C12'):
+        # if comment.startswith('# C12'):
         #    raise
         # this raises in line 2127 fro 330
         self.comments[line] = retval = FullLineComment(comment[:-1], line, column)
@@ -2102,20 +2114,28 @@ class ScannedComments:
         return self.comments[idx]
 
     def __str__(self):
-        return 'ParsedComments:\n  '  + \
-        '\n  '.join((_F('{lineno:2} {x}', lineno=lineno, x=x.info()) for lineno, x in self.comments.items())) + '\n'
+        return (
+            'ParsedComments:\n  '
+            + '\n  '.join(
+                (
+                    _F('{lineno:2} {x}', lineno=lineno, x=x.info())
+                    for lineno, x in self.comments.items()
+                )
+            )
+            + '\n'
+        )
 
     def last(self):
         lineno, x = list(self.comments.items())[-1]
-        return _F('{lineno:2} {x}\n', lineno=lineno, x=x.info()) 
+        return _F('{lineno:2} {x}\n', lineno=lineno, x=x.info())
 
     def any_unprocessed(self):
         # ToDo: might want to differentiate based on lineno
         return len(self.unused) > 0
-        #for lno, comment in reversed(self.comments.items()):
+        # for lno, comment in reversed(self.comments.items()):
         #    if comment.used == ' ':
         #        return True
-        #return False
+        # return False
 
     def unprocessed(self, use=False):
         while len(self.unused) > 0:
@@ -2132,7 +2152,7 @@ class ScannedComments:
         xprintf('assign_pre', token_line, self.unused, info.function, info.lineno)
         gobbled = False
         while self.unused and self.unused[0] < token_line:
-            gobled = True
+            gobbled = True
             first = self.unused.pop(0)
             xprintf('assign_pre < ', first)
             self.comments[first].set_used()
@@ -2147,13 +2167,21 @@ class ScannedComments:
         if not isinstance(self.comments[comment_line], EOLComment):
             return
         idx = 1
-        while tokens[-idx].start_mark.line > comment_line or isinstance(tokens[-idx], ValueToken):
+        while tokens[-idx].start_mark.line > comment_line or isinstance(
+            tokens[-idx], ValueToken
+        ):
             idx += 1
         xprintf('idx1', idx)
-        if len(tokens) > idx  and isinstance(tokens[-idx], ScalarToken) and isinstance(tokens[-(idx+1)], ScalarToken):
+        if (
+            len(tokens) > idx
+            and isinstance(tokens[-idx], ScalarToken)
+            and isinstance(tokens[-(idx + 1)], ScalarToken)
+        ):
             return
         try:
-            if isinstance(tokens[-idx], ScalarToken) and isinstance(tokens[-(idx+1)], KeyToken):
+            if isinstance(tokens[-idx], ScalarToken) and isinstance(
+                tokens[-(idx + 1)], KeyToken
+            ):
                 try:
                     eol_idx = self.unused.pop(0)
                     self.comments[eol_idx].set_used()
@@ -2166,7 +2194,9 @@ class ScannedComments:
             xprintf('IndexError1')
             pass
         try:
-            if isinstance(tokens[-idx], ScalarToken) and isinstance(tokens[-(idx+1)], (ValueToken, BlockEntryToken)):
+            if isinstance(tokens[-idx], ScalarToken) and isinstance(
+                tokens[-(idx + 1)], (ValueToken, BlockEntryToken)
+            ):
                 try:
                     eol_idx = self.unused.pop(0)
                     self.comments[eol_idx].set_used()
@@ -2180,7 +2210,9 @@ class ScannedComments:
         for t in tokens:
             xprintf('tt-', t)
         xprintf('not implemented EOL', type(tokens[-idx]))
-        import sys; sys.exit(0)
+        import sys
+
+        sys.exit(0)
 
     def assign_post(self, token):
         token_line = token.start_mark.line
@@ -2188,7 +2220,7 @@ class ScannedComments:
         xprintf('assign_post', token_line, self.unused, info.function, info.lineno)
         gobbled = False
         while self.unused and self.unused[0] < token_line:
-            gobled = True
+            gobbled = True
             first = self.unused.pop(0)
             xprintf('assign_post < ', first)
             self.comments[first].set_used()
@@ -2196,16 +2228,22 @@ class ScannedComments:
         return gobbled
 
     def str_unprocessed(self):
-        return ''.join((_F('  {ind:2} {x}\n', ind=ind, x=x.info()) for ind, x in self.comments.items() if x.used == ' '))
+        return ''.join(
+            (
+                _F('  {ind:2} {x}\n', ind=ind, x=x.info())
+                for ind, x in self.comments.items()
+                if x.used == ' '
+            )
+        )
 
 
 class RoundTripScannerSC(Scanner):  # RoundTripScanner Split Comments
     def __init__(self, *arg, **kw):
         super().__init__(*arg, **kw)
         assert self.loader is not None
-        # comments isinitialised on .need_more_tokens and persist on self.loader.parsed_comments
-        # 
-        self.comments = None 
+        # comments isinitialised on .need_more_tokens and persist on
+        # self.loader.parsed_comments
+        self.comments = None
 
     def get_token(self):
         # type: () -> Any
@@ -2240,7 +2278,7 @@ class RoundTripScannerSC(Scanner):  # RoundTripScanner Split Comments
             xprintf('-x--', len(self.tokens))
             for t in self.tokens:
                 xprintf(t)
-            #xprintf(self.comments.last())
+            # xprintf(self.comments.last())
             xprintf(self.comments.str_unprocessed())
         self.comments.assign_pre(self.tokens[0])
         self.comments.assign_eol(self.tokens)
@@ -2254,7 +2292,6 @@ class RoundTripScannerSC(Scanner):  # RoundTripScanner Split Comments
         start_mark = self.reader.get_mark()
         # xprintf('current_mark', start_mark.line, start_mark.column)
         found = False
-        idx = 0
         while not found:
             while srp() == ' ':
                 srf()
@@ -2262,7 +2299,7 @@ class RoundTripScannerSC(Scanner):  # RoundTripScanner Split Comments
             if ch == '#':
                 comment_start_mark = self.reader.get_mark()
                 comment = ch
-                srf() # skipt the '#'
+                srf()  # skipt the '#'
                 while ch not in _THE_END:
                     ch = srp()
                     if ch == '\0':  # don't gobble the end-of-stream character
@@ -2275,9 +2312,13 @@ class RoundTripScannerSC(Scanner):  # RoundTripScanner Split Comments
                     srf()
                 # we have a comment
                 if start_mark.column == 0:
-                    self.comments.add_full_line_comment(comment, comment_start_mark.column, comment_start_mark.line)
+                    self.comments.add_full_line_comment(
+                        comment, comment_start_mark.column, comment_start_mark.line
+                    )
                 else:
-                    self.comments.add_eol_comment(comment, comment_start_mark.column, comment_start_mark.line)
+                    self.comments.add_eol_comment(
+                        comment, comment_start_mark.column, comment_start_mark.line
+                    )
                     comment = ""
                 # gather any blank lines or full line comments following the comment as well
                 self.scan_empty_or_full_line_comments()
@@ -2300,7 +2341,7 @@ class RoundTripScannerSC(Scanner):  # RoundTripScanner Split Comments
                     if srp() == '#':
                         # empty line followed by indented real comment
                         comment = comment.rsplit('\n', 1)[0] + '\n'
-                    end_mark = self.reader.get_mark()
+                    _ = self.reader.get_mark()  # gobble end_mark
                     return None
             else:
                 found = True
diff --git a/serializer.py b/serializer.py
index 1a78829..cc2329d 100644
--- a/serializer.py
+++ b/serializer.py
@@ -154,7 +154,10 @@ class Serializer:
         # type: (Any, Any, Any) -> None
         alias = self.anchors[node]
         if node in self.serialized_nodes:
-            self.emitter.emit(AliasEvent(alias))
+            node_style = getattr(node, 'style', None)
+            if node_style != '?':
+                node_style = None
+            self.emitter.emit(AliasEvent(alias, style=node_style))
         else:
             self.serialized_nodes[node] = True
             self.resolver.descend_resolver(parent, index)
diff --git a/tokens.py b/tokens.py
index 01cae1f..84c90cc 100644
--- a/tokens.py
+++ b/tokens.py
@@ -1,6 +1,6 @@
 # coding: utf-8
 
-from ruamel.yaml.compat import _F, nprintf
+from ruamel.yaml.compat import _F, nprintf  # NOQA
 
 if False:  # MYPY
     from typing import Text, Any, Dict, Optional, List  # NOQA
@@ -23,10 +23,12 @@ class Token:
         #               hasattr('self', key)]
         attributes = [key for key in self.__slots__ if not key.endswith('_mark')]
         attributes.sort()
-        #arguments = ', '.join(
-        #    [_F('{key!s}={gattr!r})', key=key, gattr=getattr(self, key)) for key in attributes]
-        #)
-        arguments = [_F('{key!s}={gattr!r}', key=key, gattr=getattr(self, key)) for key in attributes]
+        # arguments = ', '.join(
+        #  [_F('{key!s}={gattr!r})', key=key, gattr=getattr(self, key)) for key in attributes]
+        # )
+        arguments = [
+            _F('{key!s}={gattr!r}', key=key, gattr=getattr(self, key)) for key in attributes
+        ]
         if SHOW_LINES:
             try:
                 arguments.append('line: ' + str(self.start_mark.line))
@@ -46,7 +48,7 @@ class Token:
     def column(self, pos):
         self.start_mark.column = pos
 
-    # old style ( <= 0.17) is a TWO element list with first being the EOL 
+    # old style ( <= 0.17) is a TWO element list with first being the EOL
     # comment concatenated with following FLC/BLNK; and second being a list of FLC/BLNK
     # preceding the token
     # new style ( >= 0.17 ) is a THREE element list with the first being a list of
@@ -62,8 +64,8 @@ class Token:
         if not hasattr(self, '_comment'):
             self._comment = [None, None]
         else:
-            assert len(self._comment) == 2 # make sure it is version 0
-        #if isinstance(comment, CommentToken):
+            assert len(self._comment) == 2  # make sure it is version 0
+        # if isinstance(comment, CommentToken):
         #    if comment.value.startswith('# C09'):
         #        raise
         self._comment[0] = comment
@@ -74,7 +76,7 @@ class Token:
         if not hasattr(self, '_comment'):
             self._comment = [None, None]
         else:
-            assert len(self._comment) == 2 # make sure it is version 0
+            assert len(self._comment) == 2  # make sure it is version 0
         assert self._comment[1] is None
         self._comment[1] = comments
         return
@@ -110,10 +112,9 @@ class Token:
                 self._comment[2] = []
         self._comment[2].append(comment)
 
-
-    #def get_comment(self):
-    #    # type: () -> Any
-    #    return getattr(self, '_comment', None)
+    # def get_comment(self):
+    #     # type: () -> Any
+    #     return getattr(self, '_comment', None)
 
     @property
     def comment(self):
@@ -347,7 +348,7 @@ class CommentToken(Token):
     def __init__(self, value, start_mark=None, end_mark=None, column=None):
         # type: (Any, Any, Any) -> None
         if start_mark is None:
-            assert columns is not None
+            assert column is not None
             self._column = column
         Token.__init__(self, start_mark, None)
         self._value = value