dont skip formatting #%%

Author: MarcoGorelli

CHANGES.md

@@ -10,6 +10,8 @@
 
 <!-- Changes that affect Black's stable style -->
 
+- Code cell separators `#%%` are now standardised to `# %%` (#2919)
+
 ### Preview style
 
 <!-- Changes that affect Black's preview style -->

src/black/comments.py

@@ -105,15 +105,14 @@ def list_comments(prefix: str, *, is_endmarker: bool) -> List[ProtoComment]:
 def make_comment(content: str) -> str:
     """Return a consistently formatted comment from the given `content` string.
 
-    All comments (except for "##", "#!", "#:", '#'", "#%%") should have a single
+    All comments (except for "##", "#!", "#:", '#'") should have a single
     space between the hash sign and the content.
 
     If `content` didn't start with a hash sign, one is provided.
     """
     content = content.rstrip()
     if not content:
         return "#"
-
     if content[0] == "#":
         content = content[1:]
     NON_BREAKING_SPACE = " "
@@ -123,7 +122,7 @@ def make_comment(content: str) -> str:
         and not content.lstrip().startswith("type:")
     ):
         content = " " + content[1:]  # Replace NBSP by a simple space
-    if content and content[0] not in " !:#'%":
+    if content and content[0] not in " !:#'":
         content = " " + content
     return "#" + content
 

tests/data/comments3.py

@@ -1,4 +1,6 @@
 # The percent-percent comments are Spyder IDE cells.
+# Both `#%%`` and `# %%` are accepted, so `black` standardises
+# to the latter.
 
 #%%
 def func():
@@ -44,4 +46,56 @@ def func():
     )
 
 
-#%%
+#%%
+
+# output
+
+# The percent-percent comments are Spyder IDE cells.
+# Both `#%%`` and `# %%` are accepted, so `black` standardises
+# to the latter.
+
+# %%
+def func():
+    x = """
+    a really long string
+    """
+    lcomp3 = [
+        # This one is actually too long to fit in a single line.
+        element.split("\n", 1)[0]
+        # yup
+        for element in collection.select_elements()
+        # right
+        if element is not None
+    ]
+    # Capture each of the exceptions in the MultiError along with each of their causes and contexts
+    if isinstance(exc_value, MultiError):
+        embedded = []
+        for exc in exc_value.exceptions:
+            if exc not in _seen:
+                embedded.append(
+                    # This should be left alone (before)
+                    traceback.TracebackException.from_exception(
+                        exc,
+                        limit=limit,
+                        lookup_lines=lookup_lines,
+                        capture_locals=capture_locals,
+                        # copy the set of _seen exceptions so that duplicates
+                        # shared between sub-exceptions are not omitted
+                        _seen=set(_seen),
+                    )
+                    # This should be left alone (after)
+                )
+
+    # everything is fine if the expression isn't nested
+    traceback.TracebackException.from_exception(
+        exc,
+        limit=limit,
+        lookup_lines=lookup_lines,
+        capture_locals=capture_locals,
+        # copy the set of _seen exceptions so that duplicates
+        # shared between sub-exceptions are not omitted
+        _seen=set(_seen),
+    )
+
+
+# %%