From 20a89abdc397cb9fbe322c7c04cd661ecfe571c3 Mon Sep 17 00:00:00 2001
From: Patrick Peglar <patrick.peglar@metoffice.gov.uk>
Date: Tue, 31 Mar 2026 01:22:08 +0100
Subject: [PATCH 1/2] Make strings of date units cftime-compatible.

---
 src/cfpint/_core.py            | 10 +++++
 src/cfpint/tests/test_basic.py | 72 ++++++++++++++++++++++++++++++----
 2 files changed, 75 insertions(+), 7 deletions(-)

diff --git a/src/cfpint/_core.py b/src/cfpint/_core.py
index 2e594f3..9f98cc6 100644
--- a/src/cfpint/_core.py
+++ b/src/cfpint/_core.py
@@ -90,6 +90,16 @@ def __str__(self):
             # TODO: we really ought to have this, but see temporary test_pintunit
             # if self.calendar_string not in (None, "default"):
             #     result += f", calendar='{self.calendar_string!s}'"
+        if self.dimensionality == {"[time]": 1}:
+            # Date or time units *only* : replace time unit symbols with full names.
+            # Required for cftime compatibility of date units:  Do the same to time
+            # (period) units also, for consistency.
+            sym_names = {"d": "days", "h": "hours", "min": "minutes", "s": "seconds"}
+            for sym, name in sym_names.items():
+                if result == sym:
+                    result = name
+                elif result.startswith(sym + " "):
+                    result = result.replace(sym + " ", name + " ", 1)
         return result
 
     def __repr__(self):
diff --git a/src/cfpint/tests/test_basic.py b/src/cfpint/tests/test_basic.py
index 426f5fc..17cb122 100644
--- a/src/cfpint/tests/test_basic.py
+++ b/src/cfpint/tests/test_basic.py
@@ -1,15 +1,10 @@
+import cftime
 import pint
 import pytest
 from cf_units import Unit as CFU_Unit
 
-# from cfpint import install_defaults
 from cfpint import Unit
 
-# TODO: want to know why this didn't work
-# @pytest.fixture(scope="session")
-# def install():
-#     install_defaults()
-
 
 class TestBasicCflike:
     """Basic behaviours copied from cf_xarray.unit."""
@@ -136,7 +131,7 @@ def test_str_repr(self, calendar, method):
         kwargs = {} if calendar is None else {"calendar": calendar}
         date_unit = Unit("day since 1970", **kwargs)
         # TODO: fix this (d//days), but for now it is done in Iris ???
-        expect = "d since 1970"
+        expect = "days since 1970"
         if calendar == "365_day" and method != "str":
             expect += "', calendar='365_day"
         if method == "str":
@@ -145,3 +140,66 @@ def test_str_repr(self, calendar, method):
             expect = f"<Unit('{expect}')>"
             result = repr(date_unit)
         assert result == expect
+
+
+# Period symbols and their name expansions:  N.B. minutes are "min" not "m"
+_TIME_SYMBOLS_NAMES = {"d": "days", "h": "hours", "min": "minutes", "s": "seconds"}
+
+
+class TestTimeunitStrings:
+    """Check the special handling of times and dates by Unit.str().
+
+    Ensures that strings of date units use cftime-compatible period names,
+    and that time-period units look the same way (for consistency).
+    """
+
+    @pytest.fixture(params=list(_TIME_SYMBOLS_NAMES))
+    def period_symbol(self, request):
+        return request.param
+
+    def test_timeperiod_strs(self, period_symbol):
+        # Test that time-period names appear in time-period unit strings.
+        # Create a unit based on the pint symbol for d/h/m/s
+        unit_str = period_symbol
+        unit = Unit(unit_str)
+
+        # in all cases should have dimensions [time], and *not* be a "date"
+        assert unit.dimensionality == {"[time]": 1}
+        assert not unit.is_datelike()
+
+        # Test that str() replaces the symbol with the name.
+        result = str(unit)
+        expected = _TIME_SYMBOLS_NAMES[period_symbol]
+        assert result == expected
+
+    def test_dateunit_conversion(self, period_symbol):
+        # Test that time-period names appear in date unit strings.
+        # Create a unit based on the pint symbol for d/h/m/s
+        unit_str = period_symbol + " since 2000-01-01"
+
+        # construct the unit
+        unit = Unit(unit_str)
+
+        # in all cases should have dimensions [time], and be a "date"
+        # TODO: one day, 'date' may be coded as a separate *dimension* ?
+        assert unit.dimensionality == {"[time]": 1}
+        assert unit.is_datelike()
+
+        # Test the expected string repr
+        result = str(unit)
+        # Expected content has a standardised name in place of the symbol.
+        expected = _TIME_SYMBOLS_NAMES[period_symbol] + " since 2000-01-01"
+        assert result == expected
+
+    def test_dateunit_cftime_compatible(self, period_symbol):
+        # Check that date unit strings are valid cftime units.
+
+        # Create a unit based on the pint symbol for d/h/m/s
+        unit_in = period_symbol + " since 2000-01-01"
+
+        # convert to a unit string
+        unit_out = str(Unit(unit_in))
+
+        # Check that the date unit is compatible with cftime
+        date = cftime.num2date(0.0, str(unit_out))
+        assert date == cftime.datetime(2000, 1, 1)

From cee1cbda770355e4fb40bd0beba4e222eaa10f6c Mon Sep 17 00:00:00 2001
From: Patrick Peglar <patrick.peglar@metoffice.gov.uk>
Date: Tue, 31 Mar 2026 01:22:51 +0100
Subject: [PATCH 2/2] Temporarily avoid line-length clash between flake8 and
 black.

---
 .flake8 | 2 ++
 1 file changed, 2 insertions(+)
 create mode 100644 .flake8

diff --git a/.flake8 b/.flake8
new file mode 100644
index 0000000..2bcd70e
--- /dev/null
+++ b/.flake8
@@ -0,0 +1,2 @@
+[flake8]
+max-line-length = 88