BUG: interval_range with float step (pandas-dev#54477)

Author: mroeschke

doc/source/whatsnew/v2.1.0.rst

@@ -737,6 +737,7 @@ Interval
 ^^^^^^^^
 - :meth:`IntervalIndex.get_indexer` and :meth:`IntervalIndex.get_indexer_nonunique` raising if ``target`` is read-only array (:issue:`53703`)
 - Bug in :class:`IntervalDtype` where the object could be kept alive when deleted (:issue:`54184`)
+- Bug in :func:`interval_range` where a float ``step`` would produce incorrect intervals from floating point artifacts (:issue:`54477`)
 
 Indexing
 ^^^^^^^^

pandas/core/indexes/interval.py

@@ -1121,19 +1121,19 @@ def interval_range(
     breaks: np.ndarray | TimedeltaIndex | DatetimeIndex
 
     if is_number(endpoint):
-        # force consistency between start/end/freq (lower end if freq skips it)
         if com.all_not_none(start, end, freq):
-            end -= (end - start) % freq
-
-        # compute the period/start/end if unspecified (at most one)
-        if periods is None:
-            periods = int((end - start) // freq) + 1
-        elif start is None:
-            start = end - (periods - 1) * freq
-        elif end is None:
-            end = start + (periods - 1) * freq
-
-        breaks = np.linspace(start, end, periods)
+            # 0.1 ensures we capture end
+            breaks = np.arange(start, end + (freq * 0.1), freq)
+        else:
+            # compute the period/start/end if unspecified (at most one)
+            if periods is None:
+                periods = int((end - start) // freq) + 1
+            elif start is None:
+                start = end - (periods - 1) * freq
+            elif end is None:
+                end = start + (periods - 1) * freq
+
+            breaks = np.linspace(start, end, periods)
         if all(is_integer(x) for x in com.not_none(start, end, freq)):
             # np.linspace always produces float output
 

pandas/tests/indexes/interval/test_interval_range.py

@@ -353,3 +353,13 @@ def test_errors(self):
         msg = "Start and end cannot both be tz-aware with different timezones"
         with pytest.raises(TypeError, match=msg):
             interval_range(start=start, end=end)
+
+    def test_float_freq(self):
+        # GH 54477
+        result = interval_range(0, 1, freq=0.1)
+        expected = IntervalIndex.from_breaks([0 + 0.1 * n for n in range(11)])
+        tm.assert_index_equal(result, expected)
+
+        result = interval_range(0, 1, freq=0.6)
+        expected = IntervalIndex.from_breaks([0, 0.6])
+        tm.assert_index_equal(result, expected)