From 32ef14501575aee447256546373a9f4e587e22e5 Mon Sep 17 00:00:00 2001
From: Jody Klymak <jklymak@gmail.com>
Date: Mon, 20 Jul 2020 14:36:32 -0700
Subject: [PATCH] FIX: undeprecate and udate num2epoch/epoch2num

---
 .../deprecations/17983-JMK.rst                |  8 ++++
 lib/matplotlib/dates.py                       | 38 +++++++++++++++----
 lib/matplotlib/tests/test_dates.py            | 12 ++++++
 3 files changed, 51 insertions(+), 7 deletions(-)
 create mode 100644 doc/api/next_api_changes/deprecations/17983-JMK.rst

diff --git a/doc/api/next_api_changes/deprecations/17983-JMK.rst b/doc/api/next_api_changes/deprecations/17983-JMK.rst
new file mode 100644
index 000000000000..4559b9919e6a
--- /dev/null
+++ b/doc/api/next_api_changes/deprecations/17983-JMK.rst
@@ -0,0 +1,8 @@
+Reverted deprecation of `~.dates.num2epoch` and `~.dates.epoch2num`
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These two functions were deprecated in 3.3.0, and did not return
+an accurate Matplotlib datenum relative to the new Matplotlib epoch
+handling (`~.dates.get_epoch` and :rc:`date.epoch`).  This version
+reverts the deprecation and fixes those functions to work with
+`~.dates.get_epoch`. 
diff --git a/lib/matplotlib/dates.py b/lib/matplotlib/dates.py
index 131eac48093c..2dd2a0e9fb79 100644
--- a/lib/matplotlib/dates.py
+++ b/lib/matplotlib/dates.py
@@ -1750,21 +1750,45 @@ def _get_interval(self):
         return self._interval
 
 
-@cbook.deprecated("3.3")
 def epoch2num(e):
     """
-    Convert an epoch or sequence of epochs to the new date format,
-    that is days since 0001.
+    Convert UNIX time to days since Matplotlib epoch.
+
+    Parameters
+    ----------
+    e : list of floats
+        Time in seconds since 1970-01-01.
+
+    Returns
+    -------
+    `numpy.array`
+        Time in days since Matplotlib epoch (see `~.dates.get_epoch()`).
     """
-    return EPOCH_OFFSET + np.asarray(e) / SEC_PER_DAY
+
+    dt = (np.datetime64('1970-01-01T00:00:00', 's') -
+          np.datetime64(get_epoch(), 's')).astype(float)
+
+    return (dt + np.asarray(e)) / SEC_PER_DAY
 
 
-@cbook.deprecated("3.3")
 def num2epoch(d):
     """
-    Convert days since 0001 to epoch.  *d* can be a number or sequence.
+    Convert days since Matplotlib epoch to UNIX time.
+
+    Parameters
+    ----------
+    d : list of floats
+        Time in days since Matplotlib epoch (see `~.dates.get_epoch()`).
+
+    Returns
+    -------
+    `numpy.array`
+        Time in seconds since 1970-01-01.
     """
-    return (np.asarray(d) - EPOCH_OFFSET) * SEC_PER_DAY
+    dt = (np.datetime64('1970-01-01T00:00:00', 's') -
+          np.datetime64(get_epoch(), 's')).astype(float)
+
+    return np.asarray(d) * SEC_PER_DAY - dt
 
 
 @cbook.deprecated("3.2")
diff --git a/lib/matplotlib/tests/test_dates.py b/lib/matplotlib/tests/test_dates.py
index 47634befc013..a446d3fd3c5c 100644
--- a/lib/matplotlib/tests/test_dates.py
+++ b/lib/matplotlib/tests/test_dates.py
@@ -998,3 +998,15 @@ def test_change_interval_multiples():
     fig.canvas.draw()
     assert ax.get_xticklabels()[0].get_text() == 'Jan 15 2020'
     assert ax.get_xticklabels()[1].get_text() == 'Feb 01 2020'
+
+
+def test_epoch2num():
+    mdates._reset_epoch_test_example()
+    mdates.set_epoch('0000-12-31')
+    assert mdates.epoch2num(86400) == 719164.0
+    assert mdates.num2epoch(719165.0) == 86400 * 2
+    # set back to the default
+    mdates._reset_epoch_test_example()
+    mdates.set_epoch('1970-01-01T00:00:00')
+    assert mdates.epoch2num(86400) == 1.0
+    assert mdates.num2epoch(2.0) == 86400 * 2