ENH: add rcParam for ConciseDate and interval_multiples

doc/users/next_whats_new/rcparams_dates.rst

@@ -0,0 +1,31 @@
+New rcParams for dates: set converter and whether to use interval_multiples
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The new :rc:`date.converter` allows toggling between
+`matplotlib.dates.DateConverter` and `matplotlib.dates.ConciseDateConverter`
+using the strings 'auto' and 'concise' respectively.
+
+The new :rc:`date.interval_multiples` allows toggling between the dates
+locator trying to pick ticks at set intervals (i.e. day 1 and 15 of the
+month), versus evenly spaced ticks that start where ever the
+timeseries starts:
+
+.. plot::
+    :include-source: True
+
+    import matplotlib.pyplot as plt
+    import numpy as np
+
+    dates = np.arange('2001-01-10', '2001-05-23', dtype='datetime64[D]')
+    y = np.sin(dates.astype(float) / 10)
+    fig, axs = plt.subplots(nrows=2, constrained_layout=True)
+
+    plt.rcParams['date.converter'] = 'concise'
+    plt.rcParams['date.interval_multiples'] = True
+    ax = axs[0]
+    ax.plot(dates, y)
+
+    plt.rcParams['date.converter'] = 'auto'
+    plt.rcParams['date.interval_multiples'] = False
+    ax = axs[1]
+    ax.plot(dates, y)

lib/matplotlib/dates.py

@@ -1834,8 +1834,11 @@ class DateConverter(units.ConversionInterface):
     The 'unit' tag for such data is None or a tzinfo instance.
     """
 
-    @staticmethod
-    def axisinfo(unit, axis):
+    def __init__(self, *, interval_multiples=True):
+        self._interval_multiples = interval_multiples
+        super().__init__()
+
+    def axisinfo(self, unit, axis):
         """
         Return the `~matplotlib.units.AxisInfo` for *unit*.
 
@@ -1844,7 +1847,8 @@ def axisinfo(unit, axis):
         """
         tz = unit
 
-        majloc = AutoDateLocator(tz=tz)
+        majloc = AutoDateLocator(tz=tz,
+                                 interval_multiples=self._interval_multiples)
         majfmt = AutoDateFormatter(majloc, tz=tz)
         datemin = datetime.date(2000, 1, 1)
         datemax = datetime.date(2010, 1, 1)
@@ -1886,17 +1890,19 @@ class ConciseDateConverter(DateConverter):
     # docstring inherited
 
     def __init__(self, formats=None, zero_formats=None, offset_formats=None,
-                 show_offset=True):
+                 show_offset=True, *, interval_multiples=True):
         self._formats = formats
         self._zero_formats = zero_formats
         self._offset_formats = offset_formats
         self._show_offset = show_offset
+        self._interval_multiples = interval_multiples
         super().__init__()
 
     def axisinfo(self, unit, axis):
         # docstring inherited
         tz = unit
-        majloc = AutoDateLocator(tz=tz)
+        majloc = AutoDateLocator(tz=tz,
+                                 interval_multiples=self._interval_multiples)
         majfmt = ConciseDateFormatter(majloc, tz=tz, formats=self._formats,
                                       zero_formats=self._zero_formats,
                                       offset_formats=self._offset_formats,
@@ -1907,6 +1913,42 @@ def axisinfo(self, unit, axis):
                               default_limits=(datemin, datemax))
 
 
-units.registry[np.datetime64] = DateConverter()
-units.registry[datetime.date] = DateConverter()
-units.registry[datetime.datetime] = DateConverter()
+class _rcParam_helper:
+    """
+    This helper class is so that we can set the converter for dates
+    via the validator for the rcParams `date.converter` and
+    `date.interval_multiples`.  Never instatiated.
+    """
+
+    conv_st = 'auto'
+    int_mult = True
+
+    @classmethod
+    def set_converter(cls, s):
+        """Called by validator for rcParams date.converter"""
+        cls.conv_st = s
+        cls.register_converters()
+
+    @classmethod
+    def set_int_mult(cls, b):
+        """Called by validator for rcParams date.interval_multiples"""
+        cls.int_mult = b
+        cls.register_converters()
+
+    @classmethod
+    def register_converters(cls):
+        """
+        Helper to register the date converters when rcParams `date.converter`
+        and `date.interval_multiples` are changed.  Called by the helpers
+        above.
+        """
+        if cls.conv_st == 'concise':
+            converter = ConciseDateConverter
+        else:
+            converter = DateConverter
+
+        interval_multiples = cls.int_mult
+        convert = converter(interval_multiples=interval_multiples)
+        units.registry[np.datetime64] = convert
+        units.registry[datetime.date] = convert
+        units.registry[datetime.datetime] = convert

lib/matplotlib/rcsetup.py

@@ -20,6 +20,7 @@
 import operator
 import os
 import re
+import sys
 
 import numpy as np
 
@@ -174,6 +175,23 @@ def validate_bool_maybe_none(b):
         raise ValueError('Could not convert "%s" to bool' % b)
 
 
+def _validate_date_converter(s):
+    s = validate_string(s)
+    mdates = sys.modules.get("matplotlib.dates")
+    if mdates:
+        mdates._rcParam_helper.set_converter(s)
+
+
+def _validate_date_int_mult(s):
+    if s is None:
+        return
+    s = validate_bool(s)
+    # only do this if dates is already imported...
+    mdates = sys.modules.get("matplotlib.dates")
+    if mdates:
+        mdates._rcParam_helper.set_int_mult(s)
+
+
 def _validate_tex_preamble(s):
     if s is None or s == 'None':
         cbook.warn_deprecated(
@@ -1271,13 +1289,19 @@ def _convert_validator_spec(key, conv):
     "date.autoformatter.second":      validate_string,
     "date.autoformatter.microsecond": validate_string,
 
+    # 'auto', 'concise', 'auto-noninterval'
+    'date.converter': _validate_date_converter,
+    # for auto date locator, choose interval_multiples
+    'date.interval_multiples': _validate_date_int_mult,
+
     # legend properties
     "legend.fancybox": validate_bool,
     "legend.loc": _ignorecase([
         "best",
         "upper right", "upper left", "lower left", "lower right", "right",
         "center left", "center right", "lower center", "upper center",
         "center"]),
+
     # the number of points in the legend line
     "legend.numpoints":      validate_int,
     # the number of points in the legend line for scatter

lib/matplotlib/tests/test_dates.py

@@ -958,3 +958,41 @@ def test_warn_notintervals():
                               mdates.date2num(dates[-1]))
     with pytest.warns(UserWarning, match="AutoDateLocator was unable") as rec:
         locs = locator()
+
+
+def test_change_converter():
+    plt.rcParams['date.converter'] = 'concise'
+    dates = np.arange('2020-01-01', '2020-05-01', dtype='datetime64[D]')
+    fig, ax = plt.subplots()
+
+    ax.plot(dates, np.arange(len(dates)))
+    fig.canvas.draw()
+    assert ax.get_xticklabels()[0].get_text() == 'Jan'
+    assert ax.get_xticklabels()[1].get_text() == '15'
+
+    plt.rcParams['date.converter'] = 'auto'
+    fig, ax = plt.subplots()
+
+    ax.plot(dates, np.arange(len(dates)))
+    fig.canvas.draw()
+    assert ax.get_xticklabels()[0].get_text() == 'Jan 01 2020'
+    assert ax.get_xticklabels()[1].get_text() == 'Jan 15 2020'
+
+
+def test_change_interval_multiples():
+    plt.rcParams['date.interval_multiples'] = False
+    dates = np.arange('2020-01-10', '2020-05-01', dtype='datetime64[D]')
+    fig, ax = plt.subplots()
+
+    ax.plot(dates, np.arange(len(dates)))
+    fig.canvas.draw()
+    assert ax.get_xticklabels()[0].get_text() == 'Jan 10 2020'
+    assert ax.get_xticklabels()[1].get_text() == 'Jan 24 2020'
+
+    plt.rcParams['date.interval_multiples'] = 'True'
+    fig, ax = plt.subplots()
+
+    ax.plot(dates, np.arange(len(dates)))
+    fig.canvas.draw()
+    assert ax.get_xticklabels()[0].get_text() == 'Jan 15 2020'
+    assert ax.get_xticklabels()[1].get_text() == 'Feb 01 2020'

matplotlibrc.template

@@ -442,10 +442,13 @@
 #date.autoformatter.minute:      %d %H:%M
 #date.autoformatter.second:      %H:%M:%S
 #date.autoformatter.microsecond: %M:%S.%f
-
 ## The reference date for Matplotlib's internal date representation
 ## See https://matplotlib.org/examples/ticks_and_spines/date_precision_and_epochs.py
 #date.epoch: 1970-01-01T00:00:00
+## 'auto', 'concise':
+#date.converter:                  auto
+## For auto converter whether to use interval_multiples:
+#date.interval_multiples:         True
 
 ## ***************************************************************************
 ## * TICKS                                                                   *