]> git.madduck.net Git - etc/vim.git/blobdiff - black.py

madduck's git repository

Every one of the projects in this repository is available at the canonical URL git://git.madduck.net/madduck/pub/<projectpath> — see each project's metadata for the exact URL.

All patches and comments are welcome. Please squash your changes to logical commits before using git-format-patch and git-send-email to patches@git.madduck.net. If you'd read over the Git project's submission guidelines and adhered to them, I'd be especially grateful.

SSH access, as well as push access can be individually arranged.

If you use my repositories frequently, consider adding the following snippet to ~/.gitconfig and using the third clone URL listed for each project:

[url "git://git.madduck.net/madduck/"]
  insteadOf = madduck:

Native README.md support on PyPI \o/
[etc/vim.git] / black.py
index d011483747546de1b3248dff21a88b52f9ad4649..f305e8dd79e66d76168e16e06c3fc4302e6c61e1 100644 (file)
--- a/black.py
+++ b/black.py
@@ -12,7 +12,7 @@ from typing import (
     Dict, Generic, Iterable, Iterator, List, Optional, Set, Tuple, TypeVar, Union
 )
 
     Dict, Generic, Iterable, Iterator, List, Optional, Set, Tuple, TypeVar, Union
 )
 
-from attr import attrib, dataclass, Factory
+from attr import dataclass, Factory
 import click
 
 # lib2to3 fork
 import click
 
 # lib2to3 fork
@@ -21,7 +21,7 @@ from blib2to3 import pygram, pytree
 from blib2to3.pgen2 import driver, token
 from blib2to3.pgen2.parse import ParseError
 
 from blib2to3.pgen2 import driver, token
 from blib2to3.pgen2.parse import ParseError
 
-__version__ = "18.3a1"
+__version__ = "18.3a2"
 DEFAULT_LINE_LENGTH = 88
 # types
 syms = pygram.python_symbols
 DEFAULT_LINE_LENGTH = 88
 # types
 syms = pygram.python_symbols
@@ -210,8 +210,13 @@ def format_str(src_contents: str, line_length: int) -> FileContent:
                 dst_contents += str(line)
         else:
             comments.append(current_line)
                 dst_contents += str(line)
         else:
             comments.append(current_line)
-    for comment in comments:
-        dst_contents += str(comment)
+    if comments:
+        if elt.previous_defs:
+            # Separate postscriptum comments from the last module-level def.
+            dst_contents += str(empty_line)
+            dst_contents += str(empty_line)
+        for comment in comments:
+            dst_contents += str(comment)
     return dst_contents
 
 
     return dst_contents
 
 
@@ -265,7 +270,7 @@ class Visitor(Generic[T]):
 
 @dataclass
 class DebugVisitor(Visitor[T]):
 
 @dataclass
 class DebugVisitor(Visitor[T]):
-    tree_depth: int = attrib(default=0)
+    tree_depth: int = 0
 
     def visit_default(self, node: LN) -> Iterator[T]:
         indent = ' ' * (2 * self.tree_depth)
 
     def visit_default(self, node: LN) -> Iterator[T]:
         indent = ' ' * (2 * self.tree_depth)
@@ -335,10 +340,10 @@ MATH_PRIORITY = 1
 
 @dataclass
 class BracketTracker:
 
 @dataclass
 class BracketTracker:
-    depth: int = attrib(default=0)
-    bracket_match: Dict[Tuple[Depth, NodeType], Leaf] = attrib(default=Factory(dict))
-    delimiters: Dict[LeafID, Priority] = attrib(default=Factory(dict))
-    previous: Optional[Leaf] = attrib(default=None)
+    depth: int = 0
+    bracket_match: Dict[Tuple[Depth, NodeType], Leaf] = Factory(dict)
+    delimiters: Dict[LeafID, Priority] = Factory(dict)
+    previous: Optional[Leaf] = None
 
     def mark(self, leaf: Leaf) -> None:
         if leaf.type == token.COMMENT:
 
     def mark(self, leaf: Leaf) -> None:
         if leaf.type == token.COMMENT:
@@ -357,19 +362,25 @@ class BracketTracker:
                 if leaf.type == token.STRING and self.previous.type == token.STRING:
                     self.delimiters[id(self.previous)] = STRING_PRIORITY
                 elif (
                 if leaf.type == token.STRING and self.previous.type == token.STRING:
                     self.delimiters[id(self.previous)] = STRING_PRIORITY
                 elif (
-                    leaf.type == token.NAME and
-                    leaf.value == 'for' and
-                    leaf.parent and
-                    leaf.parent.type in {syms.comp_for, syms.old_comp_for}
+                    leaf.type == token.NAME
+                    and leaf.value == 'for'
+                    and leaf.parent
+                    and leaf.parent.type in {syms.comp_for, syms.old_comp_for}
                 ):
                     self.delimiters[id(self.previous)] = COMPREHENSION_PRIORITY
                 elif (
                 ):
                     self.delimiters[id(self.previous)] = COMPREHENSION_PRIORITY
                 elif (
-                    leaf.type == token.NAME and
-                    leaf.value == 'if' and
-                    leaf.parent and
-                    leaf.parent.type in {syms.comp_if, syms.old_comp_if}
+                    leaf.type == token.NAME
+                    and leaf.value == 'if'
+                    and leaf.parent
+                    and leaf.parent.type in {syms.comp_if, syms.old_comp_if}
                 ):
                     self.delimiters[id(self.previous)] = COMPREHENSION_PRIORITY
                 ):
                     self.delimiters[id(self.previous)] = COMPREHENSION_PRIORITY
+                elif (
+                    leaf.type == token.NAME
+                    and leaf.value in LOGIC_OPERATORS
+                    and leaf.parent
+                ):
+                    self.delimiters[id(self.previous)] = LOGIC_PRIORITY
         if leaf.type in OPENING_BRACKETS:
             self.bracket_match[self.depth, BRACKET[leaf.type]] = leaf
             self.depth += 1
         if leaf.type in OPENING_BRACKETS:
             self.bracket_match[self.depth, BRACKET[leaf.type]] = leaf
             self.depth += 1
@@ -389,13 +400,13 @@ class BracketTracker:
 
 @dataclass
 class Line:
 
 @dataclass
 class Line:
-    depth: int = attrib(default=0)
-    leaves: List[Leaf] = attrib(default=Factory(list))
-    comments: Dict[LeafID, Leaf] = attrib(default=Factory(dict))
-    bracket_tracker: BracketTracker = attrib(default=Factory(BracketTracker))
-    inside_brackets: bool = attrib(default=False)
-    has_for: bool = attrib(default=False)
-    _for_loop_variable: bool = attrib(default=False, init=False)
+    depth: int = 0
+    leaves: List[Leaf] = Factory(list)
+    comments: Dict[LeafID, Leaf] = Factory(dict)
+    bracket_tracker: BracketTracker = Factory(BracketTracker)
+    inside_brackets: bool = False
+    has_for: bool = False
+    _for_loop_variable: bool = False
 
     def append(self, leaf: Leaf, preformatted: bool = False) -> None:
         has_value = leaf.value.strip()
 
     def append(self, leaf: Leaf, preformatted: bool = False) -> None:
         has_value = leaf.value.strip()
@@ -432,9 +443,9 @@ class Line:
     @property
     def is_class(self) -> bool:
         return (
     @property
     def is_class(self) -> bool:
         return (
-            bool(self) and
-            self.leaves[0].type == token.NAME and
-            self.leaves[0].value == 'class'
+            bool(self)
+            and self.leaves[0].type == token.NAME
+            and self.leaves[0].value == 'class'
         )
 
     @property
         )
 
     @property
@@ -450,37 +461,37 @@ class Line:
         except IndexError:
             second_leaf = None
         return (
         except IndexError:
             second_leaf = None
         return (
-            (first_leaf.type == token.NAME and first_leaf.value == 'def') or
-            (
-                first_leaf.type == token.NAME and
-                first_leaf.value == 'async' and
-                second_leaf is not None and
-                second_leaf.type == token.NAME and
-                second_leaf.value == 'def'
+            (first_leaf.type == token.NAME and first_leaf.value == 'def')
+            or (
+                first_leaf.type == token.NAME
+                and first_leaf.value == 'async'
+                and second_leaf is not None
+                and second_leaf.type == token.NAME
+                and second_leaf.value == 'def'
             )
         )
 
     @property
     def is_flow_control(self) -> bool:
         return (
             )
         )
 
     @property
     def is_flow_control(self) -> bool:
         return (
-            bool(self) and
-            self.leaves[0].type == token.NAME and
-            self.leaves[0].value in FLOW_CONTROL
+            bool(self)
+            and self.leaves[0].type == token.NAME
+            and self.leaves[0].value in FLOW_CONTROL
         )
 
     @property
     def is_yield(self) -> bool:
         return (
         )
 
     @property
     def is_yield(self) -> bool:
         return (
-            bool(self) and
-            self.leaves[0].type == token.NAME and
-            self.leaves[0].value == 'yield'
+            bool(self)
+            and self.leaves[0].type == token.NAME
+            and self.leaves[0].value == 'yield'
         )
 
     def maybe_remove_trailing_comma(self, closing: Leaf) -> bool:
         if not (
         )
 
     def maybe_remove_trailing_comma(self, closing: Leaf) -> bool:
         if not (
-            self.leaves and
-            self.leaves[-1].type == token.COMMA and
-            closing.type in CLOSING_BRACKETS
+            self.leaves
+            and self.leaves[-1].type == token.COMMA
+            and closing.type in CLOSING_BRACKETS
         ):
             return False
 
         ):
             return False
 
@@ -508,6 +519,10 @@ class Line:
             bracket_depth = leaf.bracket_depth
             if bracket_depth == depth and leaf.type == token.COMMA:
                 commas += 1
             bracket_depth = leaf.bracket_depth
             if bracket_depth == depth and leaf.type == token.COMMA:
                 commas += 1
+                if leaf.parent and leaf.parent.type == syms.arglist:
+                    commas += 1
+                    break
+
         if commas > 1:
             self.leaves.pop()
             return True
         if commas > 1:
             self.leaves.pop()
             return True
@@ -547,8 +562,8 @@ class Line:
         appended will appear "too long" when splitting.
         """
         if not (
         appended will appear "too long" when splitting.
         """
         if not (
-            comment.type == STANDALONE_COMMENT and
-            self.bracket_tracker.any_open_brackets()
+            comment.type == STANDALONE_COMMENT
+            and self.bracket_tracker.any_open_brackets()
         ):
             return False
 
         ):
             return False
 
@@ -605,11 +620,13 @@ class EmptyLineTracker:
     """Provides a stateful method that returns the number of potential extra
     empty lines needed before and after the currently processed line.
 
     """Provides a stateful method that returns the number of potential extra
     empty lines needed before and after the currently processed line.
 
-    Note: this tracker works on lines that haven't been split yet.
+    Note: this tracker works on lines that haven't been split yet.  It assumes
+    the prefix of the first leaf consists of optional newlines.  Those newlines
+    are consumed by `maybe_empty_lines()` and included in the computation.
     """
     """
-    previous_line: Optional[Line] = attrib(default=None)
-    previous_after: int = attrib(default=0)
-    previous_defs: List[int] = attrib(default=Factory(list))
+    previous_line: Optional[Line] = None
+    previous_after: int = 0
+    previous_defs: List[int] = Factory(list)
 
     def maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:
         """Returns the number of extra empty lines before and after the `current_line`.
 
     def maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:
         """Returns the number of extra empty lines before and after the `current_line`.
@@ -618,17 +635,28 @@ class EmptyLineTracker:
         (two on module-level), as well as providing an extra empty line after flow
         control keywords to make them more prominent.
         """
         (two on module-level), as well as providing an extra empty line after flow
         control keywords to make them more prominent.
         """
+        if current_line.is_comment:
+            # Don't count standalone comments towards previous empty lines.
+            return 0, 0
+
         before, after = self._maybe_empty_lines(current_line)
         before, after = self._maybe_empty_lines(current_line)
+        before -= self.previous_after
         self.previous_after = after
         self.previous_line = current_line
         return before, after
 
     def _maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:
         self.previous_after = after
         self.previous_line = current_line
         return before, after
 
     def _maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:
-        before = 0
+        if current_line.leaves:
+            # Consume the first leaf's extra newlines.
+            first_leaf = current_line.leaves[0]
+            before = int('\n' in first_leaf.prefix)
+            first_leaf.prefix = ''
+        else:
+            before = 0
         depth = current_line.depth
         while self.previous_defs and self.previous_defs[-1] >= depth:
             self.previous_defs.pop()
         depth = current_line.depth
         while self.previous_defs and self.previous_defs[-1] >= depth:
             self.previous_defs.pop()
-            before = (1 if depth else 2) - self.previous_after
+            before = 1 if depth else 2
         is_decorator = current_line.is_decorator
         if is_decorator or current_line.is_def or current_line.is_class:
             if not is_decorator:
         is_decorator = current_line.is_decorator
         if is_decorator or current_line.is_def or current_line.is_class:
             if not is_decorator:
@@ -644,24 +672,23 @@ class EmptyLineTracker:
             newlines = 2
             if current_line.depth:
                 newlines -= 1
             newlines = 2
             if current_line.depth:
                 newlines -= 1
-            newlines -= self.previous_after
             return newlines, 0
 
         if current_line.is_flow_control:
             return before, 1
 
         if (
             return newlines, 0
 
         if current_line.is_flow_control:
             return before, 1
 
         if (
-            self.previous_line and
-            self.previous_line.is_import and
-            not current_line.is_import and
-            depth == self.previous_line.depth
+            self.previous_line
+            and self.previous_line.is_import
+            and not current_line.is_import
+            and depth == self.previous_line.depth
         ):
             return (before or 1), 0
 
         if (
         ):
             return (before or 1), 0
 
         if (
-            self.previous_line and
-            self.previous_line.is_yield and
-            (not current_line.is_yield or depth != self.previous_line.depth)
+            self.previous_line
+            and self.previous_line.is_yield
+            and (not current_line.is_yield or depth != self.previous_line.depth)
         ):
             return (before or 1), 0
 
         ):
             return (before or 1), 0
 
@@ -675,8 +702,8 @@ class LineGenerator(Visitor[Line]):
     Note: destroys the tree it's visiting by mutating prefixes of its leaves
     in ways that will no longer stringify to valid Python code on the tree.
     """
     Note: destroys the tree it's visiting by mutating prefixes of its leaves
     in ways that will no longer stringify to valid Python code on the tree.
     """
-    current_line: Line = attrib(default=Factory(Line))
-    standalone_comments: List[Leaf] = attrib(default=Factory(list))
+    current_line: Line = Factory(Line)
+    standalone_comments: List[Leaf] = Factory(list)
 
     def line(self, indent: int = 0) -> Iterator[Line]:
         """Generate a line.
 
     def line(self, indent: int = 0) -> Iterator[Line]:
         """Generate a line.
@@ -804,9 +831,10 @@ BRACKET = {token.LPAR: token.RPAR, token.LSQB: token.RSQB, token.LBRACE: token.R
 OPENING_BRACKETS = set(BRACKET.keys())
 CLOSING_BRACKETS = set(BRACKET.values())
 BRACKETS = OPENING_BRACKETS | CLOSING_BRACKETS
 OPENING_BRACKETS = set(BRACKET.keys())
 CLOSING_BRACKETS = set(BRACKET.values())
 BRACKETS = OPENING_BRACKETS | CLOSING_BRACKETS
+ALWAYS_NO_SPACE = CLOSING_BRACKETS | {token.COMMA, token.COLON, STANDALONE_COMMENT}
 
 
 
 
-def whitespace(leaf: Leaf) -> str:
+def whitespace(leaf: Leaf) -> str:  # noqa C901
     """Return whitespace prefix if needed for the given `leaf`."""
     NO = ''
     SPACE = ' '
     """Return whitespace prefix if needed for the given `leaf`."""
     NO = ''
     SPACE = ' '
@@ -814,24 +842,12 @@ def whitespace(leaf: Leaf) -> str:
     t = leaf.type
     p = leaf.parent
     v = leaf.value
     t = leaf.type
     p = leaf.parent
     v = leaf.value
-    if t == token.COLON:
-        return NO
-
-    if t == token.COMMA:
-        return NO
-
-    if t == token.RPAR:
+    if t in ALWAYS_NO_SPACE:
         return NO
 
     if t == token.COMMENT:
         return DOUBLESPACE
 
         return NO
 
     if t == token.COMMENT:
         return DOUBLESPACE
 
-    if t == STANDALONE_COMMENT:
-        return NO
-
-    if t in CLOSING_BRACKETS:
-        return NO
-
     assert p is not None, f"INTERNAL ERROR: hand-made leaf without parent: {leaf!r}"
     prev = leaf.prev_sibling
     if not prev:
     assert p is not None, f"INTERNAL ERROR: hand-made leaf without parent: {leaf!r}"
     prev = leaf.prev_sibling
     if not prev:
@@ -863,7 +879,7 @@ def whitespace(leaf: Leaf) -> str:
             if prevp.parent and prevp.parent.type == syms.subscript:
                 return NO
 
             if prevp.parent and prevp.parent.type == syms.subscript:
                 return NO
 
-        elif prevp.parent and prevp.parent.type == syms.factor:
+        elif prevp.parent and prevp.parent.type in {syms.factor, syms.star_expr}:
             return NO
 
     elif prev.type in OPENING_BRACKETS:
             return NO
 
     elif prev.type in OPENING_BRACKETS:
@@ -976,9 +992,9 @@ def whitespace(leaf: Leaf) -> str:
             return NO
 
     elif (
             return NO
 
     elif (
-        p.type == syms.listmaker or
-        p.type == syms.testlist_gexp or
-        p.type == syms.subscriptlist
+        p.type == syms.listmaker
+        or p.type == syms.testlist_gexp
+        or p.type == syms.subscriptlist
     ):
         # list interior, including unpacking
         if not prev:
     ):
         # list interior, including unpacking
         if not prev:
@@ -992,7 +1008,7 @@ def whitespace(leaf: Leaf) -> str:
         if prev.type == token.DOUBLESTAR:
             return NO
 
         if prev.type == token.DOUBLESTAR:
             return NO
 
-    elif p.type == syms.factor or p.type == syms.star_expr:
+    elif p.type in {syms.factor, syms.star_expr}:
         # unary ops
         if not prev:
             prevp = preceding_leaf(p)
         # unary ops
         if not prev:
             prevp = preceding_leaf(p)
@@ -1056,16 +1072,13 @@ def is_delimiter(leaf: Leaf) -> int:
     if leaf.type == token.COMMA:
         return COMMA_PRIORITY
 
     if leaf.type == token.COMMA:
         return COMMA_PRIORITY
 
-    if leaf.type == token.NAME and leaf.value in LOGIC_OPERATORS:
-        return LOGIC_PRIORITY
-
     if leaf.type in COMPARATORS:
         return COMPARATOR_PRIORITY
 
     if (
     if leaf.type in COMPARATORS:
         return COMPARATOR_PRIORITY
 
     if (
-        leaf.type in MATH_OPERATORS and
-        leaf.parent and
-        leaf.parent.type not in {syms.factor, syms.star_expr}
+        leaf.type in MATH_OPERATORS
+        and leaf.parent
+        and leaf.parent.type not in {syms.factor, syms.star_expr}
     ):
         return MATH_PRIORITY
 
     ):
         return MATH_PRIORITY
 
@@ -1102,7 +1115,7 @@ def generate_comments(leaf: Leaf) -> Iterator[Leaf]:
     if content and (content[0] not in {' ', '!', '#'}):
         content = ' ' + content
     is_standalone_comment = (
     if content and (content[0] not in {' ', '!', '#'}):
         content = ' ' + content
     is_standalone_comment = (
-        '\n' in before_comment or '\n' in content or leaf.type == token.DEDENT
+        '\n' in before_comment or '\n' in content or leaf.type == token.ENDMARKER
     )
     if not is_standalone_comment:
         # simple trailing comment
     )
     if not is_standalone_comment:
         # simple trailing comment
@@ -1185,11 +1198,11 @@ def left_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
     matching_bracket = None
     for leaf in line.leaves:
         if (
     matching_bracket = None
     for leaf in line.leaves:
         if (
-            current_leaves is body_leaves and
-            leaf.type in CLOSING_BRACKETS and
-            leaf.opening_bracket is matching_bracket
+            current_leaves is body_leaves
+            and leaf.type in CLOSING_BRACKETS
+            and leaf.opening_bracket is matching_bracket
         ):
         ):
-            current_leaves = tail_leaves
+            current_leaves = tail_leaves if body_leaves else head_leaves
         current_leaves.append(leaf)
         if current_leaves is head_leaves:
             if leaf.type in OPENING_BRACKETS:
         current_leaves.append(leaf)
         if current_leaves is head_leaves:
             if leaf.type in OPENING_BRACKETS:
@@ -1207,18 +1220,7 @@ def left_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
             comment_after = line.comments.get(id(leaf))
             if comment_after:
                 result.append(comment_after, preformatted=True)
             comment_after = line.comments.get(id(leaf))
             if comment_after:
                 result.append(comment_after, preformatted=True)
-    # Check if the split succeeded.
-    tail_len = len(str(tail))
-    if not body:
-        if tail_len == 0:
-            raise CannotSplit("Splitting brackets produced the same line")
-
-        elif tail_len < 3:
-            raise CannotSplit(
-                f"Splitting brackets on an empty body to save "
-                f"{tail_len} characters is not worth it"
-            )
-
+    split_succeeded_or_raise(head, body, tail)
     for result in (head, body, tail):
         if result:
             yield result
     for result in (head, body, tail):
         if result:
             yield result
@@ -1237,7 +1239,7 @@ def right_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
     for leaf in reversed(line.leaves):
         if current_leaves is body_leaves:
             if leaf is opening_bracket:
     for leaf in reversed(line.leaves):
         if current_leaves is body_leaves:
             if leaf is opening_bracket:
-                current_leaves = head_leaves
+                current_leaves = head_leaves if body_leaves else tail_leaves
         current_leaves.append(leaf)
         if current_leaves is tail_leaves:
             if leaf.type in CLOSING_BRACKETS:
         current_leaves.append(leaf)
         if current_leaves is tail_leaves:
             if leaf.type in CLOSING_BRACKETS:
@@ -1258,8 +1260,14 @@ def right_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
             comment_after = line.comments.get(id(leaf))
             if comment_after:
                 result.append(comment_after, preformatted=True)
             comment_after = line.comments.get(id(leaf))
             if comment_after:
                 result.append(comment_after, preformatted=True)
-    # Check if the split succeeded.
-    tail_len = len(str(tail).strip('\n'))
+    split_succeeded_or_raise(head, body, tail)
+    for result in (head, body, tail):
+        if result:
+            yield result
+
+
+def split_succeeded_or_raise(head: Line, body: Line, tail: Line) -> None:
+    tail_len = len(str(tail).strip())
     if not body:
         if tail_len == 0:
             raise CannotSplit("Splitting brackets produced the same line")
     if not body:
         if tail_len == 0:
             raise CannotSplit("Splitting brackets produced the same line")
@@ -1270,10 +1278,6 @@ def right_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
                 f"{tail_len} characters is not worth it"
             )
 
                 f"{tail_len} characters is not worth it"
             )
 
-    for result in (head, body, tail):
-        if result:
-            yield result
-
 
 def delimiter_split(line: Line, py36: bool = False) -> Iterator[Line]:
     """Split according to delimiters of the highest priority.
 
 def delimiter_split(line: Line, py36: bool = False) -> Iterator[Line]:
     """Split according to delimiters of the highest priority.
@@ -1303,9 +1307,9 @@ def delimiter_split(line: Line, py36: bool = False) -> Iterator[Line]:
             current_line.append(comment_after, preformatted=True)
         lowest_depth = min(lowest_depth, leaf.bracket_depth)
         if (
             current_line.append(comment_after, preformatted=True)
         lowest_depth = min(lowest_depth, leaf.bracket_depth)
         if (
-            leaf.bracket_depth == lowest_depth and
-            leaf.type == token.STAR or
-            leaf.type == token.DOUBLESTAR
+            leaf.bracket_depth == lowest_depth
+            and leaf.type == token.STAR
+            or leaf.type == token.DOUBLESTAR
         ):
             trailing_comma_safe = trailing_comma_safe and py36
         leaf_priority = delimiters.get(id(leaf))
         ):
             trailing_comma_safe = trailing_comma_safe and py36
         leaf_priority = delimiters.get(id(leaf))
@@ -1316,9 +1320,9 @@ def delimiter_split(line: Line, py36: bool = False) -> Iterator[Line]:
             current_line = Line(depth=line.depth, inside_brackets=line.inside_brackets)
     if current_line:
         if (
             current_line = Line(depth=line.depth, inside_brackets=line.inside_brackets)
     if current_line:
         if (
-            delimiter_priority == COMMA_PRIORITY and
-            current_line.leaves[-1].type != token.COMMA and
-            trailing_comma_safe
+            delimiter_priority == COMMA_PRIORITY
+            and current_line.leaves[-1].type != token.COMMA
+            and trailing_comma_safe
         ):
             current_line.append(Leaf(token.COMMA, ','))
         normalize_prefix(current_line.leaves[0])
         ):
             current_line.append(Leaf(token.COMMA, ','))
         normalize_prefix(current_line.leaves[0])
@@ -1331,10 +1335,10 @@ def is_import(leaf: Leaf) -> bool:
     t = leaf.type
     v = leaf.value
     return bool(
     t = leaf.type
     v = leaf.value
     return bool(
-        t == token.NAME and
-        (
-            (v == 'import' and p and p.type == syms.import_name) or
-            (v == 'from' and p and p.type == syms.import_from)
+        t == token.NAME
+        and (
+            (v == 'import' and p and p.type == syms.import_name)
+            or (v == 'from' and p and p.type == syms.import_from)
         )
     )
 
         )
     )
 
@@ -1344,9 +1348,6 @@ def normalize_prefix(leaf: Leaf) -> None:
     if is_import(leaf):
         spl = leaf.prefix.split('#', 1)
         nl_count = spl[0].count('\n')
     if is_import(leaf):
         spl = leaf.prefix.split('#', 1)
         nl_count = spl[0].count('\n')
-        if len(spl) > 1:
-            # Skip one newline since it was for a standalone comment.
-            nl_count -= 1
         leaf.prefix = '\n' * nl_count
         return
 
         leaf.prefix = '\n' * nl_count
         return
 
@@ -1367,9 +1368,9 @@ def is_python36(node: Node) -> bool:
                 return True
 
         elif (
                 return True
 
         elif (
-            n.type == syms.typedargslist and
-            n.children and
-            n.children[-1].type == token.COMMA
+            n.type == syms.typedargslist
+            and n.children
+            and n.children[-1].type == token.COMMA
         ):
             for ch in n.children:
                 if ch.type == token.STAR or ch.type == token.DOUBLESTAR:
         ):
             for ch in n.children:
                 if ch.type == token.STAR or ch.type == token.DOUBLESTAR:
@@ -1399,9 +1400,9 @@ def gen_python_files_in_dir(path: Path) -> Iterator[Path]:
 @dataclass
 class Report:
     """Provides a reformatting counter."""
 @dataclass
 class Report:
     """Provides a reformatting counter."""
-    change_count: int = attrib(default=0)
-    same_count: int = attrib(default=0)
-    failure_count: int = attrib(default=0)
+    change_count: int = 0
+    same_count: int = 0
+    failure_count: int = 0
 
     def done(self, src: Path, changed: bool) -> None:
         """Increment the counter for successful reformatting. Write out a message."""
 
     def done(self, src: Path, changed: bool) -> None:
         """Increment the counter for successful reformatting. Write out a message."""
@@ -1500,7 +1501,7 @@ def assert_equivalent(src: str, dst: str) -> None:
         raise AssertionError(
             f"INTERNAL ERROR: Black produced invalid code: {exc}. "
             f"Please report a bug on https://github.com/ambv/black/issues.  "
         raise AssertionError(
             f"INTERNAL ERROR: Black produced invalid code: {exc}. "
             f"Please report a bug on https://github.com/ambv/black/issues.  "
-            f"This invalid output might be helpful: {log}",
+            f"This invalid output might be helpful: {log}"
         ) from None
 
     src_ast_str = '\n'.join(_v(src_ast))
         ) from None
 
     src_ast_str = '\n'.join(_v(src_ast))
@@ -1511,7 +1512,7 @@ def assert_equivalent(src: str, dst: str) -> None:
             f"INTERNAL ERROR: Black produced code that is not equivalent to "
             f"the source.  "
             f"Please report a bug on https://github.com/ambv/black/issues.  "
             f"INTERNAL ERROR: Black produced code that is not equivalent to "
             f"the source.  "
             f"Please report a bug on https://github.com/ambv/black/issues.  "
-            f"This diff might be helpful: {log}",
+            f"This diff might be helpful: {log}"
         ) from None
 
 
         ) from None
 
 
@@ -1530,7 +1531,7 @@ def assert_stable(src: str, dst: str, line_length: int) -> None:
             f"INTERNAL ERROR: Black produced different code on the second pass "
             f"of the formatter.  "
             f"Please report a bug on https://github.com/ambv/black/issues.  "
             f"INTERNAL ERROR: Black produced different code on the second pass "
             f"of the formatter.  "
             f"Please report a bug on https://github.com/ambv/black/issues.  "
-            f"This diff might be helpful: {log}",
+            f"This diff might be helpful: {log}"
         ) from None
 
 
         ) from None