For the repro file its_science.py

def first_column1d(values):
    """First column, as a 1D array."""
    return values[:, 0]


def first_column2d(values):
    """First column, but still a 2D array."""
    return values[:, 0:1]

Running black (installed from HEAD as in #30)

$ venv-HEAD/bin/black its_science.py
reformatted its_science.py

changes the "exotic" slice argument:

diff --git a/its_science.py b/its_science.py
index f3c4a8b..3a5dba0 100644
--- a/its_science.py
+++ b/its_science.py
@@ -5,4 +5,4 @@ def first_column1d(values):
 
 def first_column2d(values):
     """First column, but still a 2D array."""
-    return values[:, 0:1]
+    return values[:,0:1]

PS @ambv This is my fourth and last issue (for now) and it's just "wrong" things I encountered when running this on a large codebase of mine. I am SOOOOO happy you have created black and look forward to evangelizing it in the community.