matplotlib · konmenel · Jan 17, 2025 · Jan 18, 2025 · Jan 27, 2025 · Jan 27, 2025
diff --git a/ci/mypy-stubtest-allowlist.txt b/ci/mypy-stubtest-allowlist.txt
@@ -4,7 +4,6 @@ matplotlib\.tests(\..*)?
 matplotlib\.pylab(\..*)?
 matplotlib\._.*
 matplotlib\.rcsetup\._listify_validator
-matplotlib\.rcsetup\._validate_linestyle
 matplotlib\.ft2font\.Glyph
 matplotlib\.testing\.jpl_units\..*
 matplotlib\.sphinxext(\..*)?

diff --git a/doc/users/next_whats_new/new_rcparams_grid_options.rst b/doc/users/next_whats_new/new_rcparams_grid_options.rst
@@ -0,0 +1,33 @@
+Separate styling options for major/minor grid line in rcParams
+--------------------------------------------------------------
+
+Using :rc:`grid.major.*` or :rc:`grid.minor.*` will overwrite the value in
+:rc:`grid.*` for the major and minor gridlines, respectively.
+
+.. plot::
+    :include-source: true
+    :alt: Modifying the gridlines using the new options `rcParams`
+
+    import matplotlib as mpl
+    import matplotlib.pyplot as plt
+
+
+    # Set visibility for major and minor gridlines
+    mpl.rcParams["axes.grid"] = True
+    mpl.rcParams["ytick.minor.visible"] = True
+    mpl.rcParams["xtick.minor.visible"] = True
+    mpl.rcParams["axes.grid.which"] = "both"
+
+    # Using old old values to set both major and minor properties
+    mpl.rcParams["grid.color"] = "red"
+    mpl.rcParams["grid.linewidth"] = 1
+
+    # Overwrite some values for major and minor separately
+    mpl.rcParams["grid.major.color"] = "black"
+    mpl.rcParams["grid.major.linewidth"] = 2
+    mpl.rcParams["grid.minor.linestyle"] = ":"
+    mpl.rcParams["grid.minor.alpha"] = 0.6
+
+    plt.plot([0, 1], [0, 1])
+
+    plt.show()
diff --git a/lib/matplotlib/__init__.py b/lib/matplotlib/__init__.py
@@ -1348,11 +1348,18 @@ def is_interactive():
     return rcParams['interactive']
 
 
-def _val_or_rc(val, rc_name):
+def _val_or_rc(val, *rc_names):
     """
-    If *val* is None, return ``mpl.rcParams[rc_name]``, otherwise return val.
+    If *val* is None, the first not-None value in ``mpl.rcParams[rc_names[i]]``.
+    If all are None returns ``mpl.rcParams[rc_names[-1]]``.
     """
-    return val if val is not None else rcParams[rc_name]
+    if val is not None:
+        return val
+
+    for rc_name in rc_names[:-1]:
+        if rcParams[rc_name] is not None:
+            return rcParams[rc_name]
+    return rcParams[rc_names[-1]]
 
 
 def _init_tests():

diff --git a/lib/matplotlib/axis.py b/lib/matplotlib/axis.py
@@ -124,16 +124,41 @@ def __init__(
                 zorder = mlines.Line2D.zorder
         self._zorder = zorder
 
-        grid_color = mpl._val_or_rc(grid_color, "grid.color")
-        grid_linestyle = mpl._val_or_rc(grid_linestyle, "grid.linestyle")
-        grid_linewidth = mpl._val_or_rc(grid_linewidth, "grid.linewidth")
+        grid_color = (
+            mpl._val_or_rc(
+                grid_color,
+                f"grid.{major_minor}.color",
+                "grid.color",
+            )
+        )
+        grid_linestyle = (
+            mpl._val_or_rc(
+                grid_linestyle,
+                f"grid.{major_minor}.linestyle",
+                "grid.linestyle",
+            )
+        )
+        grid_linewidth = (
+            mpl._val_or_rc(
+                grid_linewidth,
+                f"grid.{major_minor}.linewidth",
+                "grid.linewidth",
+            )
+        )
         if grid_alpha is None and not mcolors._has_alpha_channel(grid_color):
             # alpha precedence: kwarg > color alpha > rcParams['grid.alpha']
             # Note: only resolve to rcParams if the color does not have alpha
             # otherwise `grid(color=(1, 1, 1, 0.5))` would work like
             #   grid(color=(1, 1, 1, 0.5), alpha=rcParams['grid.alpha'])
             # so the that the rcParams default would override color alpha.
-            grid_alpha = mpl.rcParams["grid.alpha"]
+            grid_alpha = (
+                # grid_alpha is None so we can use the first key
+                mpl._val_or_rc(
+                    mpl.rcParams[f"grid.{major_minor}.alpha"],
+                    "grid.alpha",
+                )
+            )
+
         grid_kw = {k[5:]: v for k, v in kwargs.items() if k != "rotation_mode"}
 
         self.tick1line = mlines.Line2D(

diff --git a/lib/matplotlib/mpl-data/matplotlibrc b/lib/matplotlib/mpl-data/matplotlibrc
@@ -538,6 +538,16 @@
 #grid.linewidth: 0.8        # in points
 #grid.alpha:     1.0        # transparency, between 0.0 and 1.0
 
+#grid.major.color:     None # If None defaults to grid.color
+#grid.major.linestyle: None # If None defaults to grid.linestyle
+#grid.major.linewidth: None # If None defaults to grid.linewidth
+#grid.major.alpha:     None # If None defaults to grid.alpha
+
+#grid.minor.color:     None # If None defaults to grid.color
+#grid.minor.linestyle: None # If None defaults to grid.linestyle
+#grid.minor.linewidth: None # If None defaults to grid.linewidth
+#grid.minor.alpha:     None # If None defaults to grid.alpha
+
 
 ## ***************************************************************************
 ## * LEGEND                                                                  *

diff --git a/lib/matplotlib/rcsetup.py b/lib/matplotlib/rcsetup.py
@@ -368,6 +368,12 @@ def validate_color(s):
     raise ValueError(f'{s!r} does not look like a color arg')
 
 
+def validate_color_or_None(s):
+    if s is None or cbook._str_equal(s, "None"):
+        return None
+    return validate_color(s)
+
+
 validate_colorlist = _listify_validator(
     validate_color, allow_stringlist=True, doc='return a list of colorspecs')
 
@@ -522,6 +528,13 @@ def _is_iterable_not_string_like(x):
     raise ValueError(f"linestyle {ls!r} is not a valid on-off ink sequence.")
 
 
+def _validate_linestyle_or_None(ls):
+    if ls is None or cbook._str_equal(ls, "None"):
+        return None
+
+    return _validate_linestyle(ls)
+
+
 validate_fillstyle = ValidateInStrings(
     'markers.fillstyle', ['full', 'left', 'right', 'bottom', 'top', 'none'])
 
@@ -1248,6 +1261,16 @@ def _convert_validator_spec(key, conv):
     "grid.linewidth":    validate_float,     # in points
     "grid.alpha":        validate_float,
 
+    "grid.major.color":        validate_color_or_None,  # grid color
+    "grid.major.linestyle":    _validate_linestyle_or_None,  # solid
+    "grid.major.linewidth":    validate_float_or_None,     # in points
+    "grid.major.alpha":        validate_float_or_None,
+
+    "grid.minor.color":        validate_color_or_None,  # grid color
+    "grid.minor.linestyle":    _validate_linestyle_or_None,  # solid
+    "grid.minor.linewidth":    validate_float_or_None,     # in points
+    "grid.minor.alpha":        validate_float_or_None,
+
     ## figure props
     # figure title
     "figure.titlesize":   validate_fontsize,

diff --git a/lib/matplotlib/rcsetup.pyi b/lib/matplotlib/rcsetup.pyi
@@ -51,6 +51,7 @@ def validate_color_or_auto(s: Any) -> ColorType | Literal["auto"]: ...
 def _validate_color_or_edge(s: Any) -> ColorType | Literal["edge"]: ...
 def validate_color_for_prop_cycle(s: Any) -> ColorType: ...
 def validate_color(s: Any) -> ColorType: ...
+def validate_color_or_None(s: Any) -> ColorType | None: ...
 def validate_colorlist(s: Any) -> list[ColorType]: ...
 def _validate_color_or_linecolor(
     s: Any,
@@ -139,7 +140,8 @@ def validate_fillstylelist(
     s: Any,
 ) -> list[Literal["full", "left", "right", "bottom", "top", "none"]]: ...
 def validate_markevery(s: Any) -> MarkEveryType: ...
-def _validate_linestyle(s: Any) -> LineStyleType: ...
+def _validate_linestyle(ls: Any) -> LineStyleType: ...
+def _validate_linestyle_or_None(ls: Any) -> LineStyleType | None: ...
 def validate_markeverylist(s: Any) -> list[MarkEveryType]: ...
 def validate_bbox(s: Any) -> Literal["tight", "standard"] | None: ...
 def validate_sketch(s: Any) -> None | tuple[float, float, float]: ...

diff --git a/lib/matplotlib/tests/test_axis.py b/lib/matplotlib/tests/test_axis.py
@@ -67,3 +67,31 @@ def test_get_tick_position_tick_params():
                    right=True, labelright=True, left=False, labelleft=False)
     assert ax.xaxis.get_ticks_position() == "top"
     assert ax.yaxis.get_ticks_position() == "right"
+
+
+def test_grid_rcparams():
+    """Tests that `grid.major/minor.*` overwrites `grid.*` in rcParams."""
+    plt.rcParams.update({
+        "axes.grid": True, "axes.grid.which": "both",
+        "ytick.minor.visible": True, "xtick.minor.visible": True,
+    })
+    def_linewidth = plt.rcParams["grid.linewidth"]
+    def_linestyle = plt.rcParams["grid.linestyle"]
+    def_alpha = plt.rcParams["grid.alpha"]
+
+    plt.rcParams.update({
+        "grid.color": "gray", "grid.minor.color": "red",
+        "grid.major.linestyle": ":", "grid.major.linewidth": 2,
+        "grid.minor.alpha": 0.6,
+    })
+    _, ax = plt.subplots()
+    ax.plot([0, 1])
+
+    assert ax.xaxis.get_major_ticks()[0].gridline.get_color() == "gray"
+    assert ax.xaxis.get_minor_ticks()[0].gridline.get_color() == "red"
+    assert ax.xaxis.get_major_ticks()[0].gridline.get_linewidth() == 2
+    assert ax.xaxis.get_minor_ticks()[0].gridline.get_linewidth() == def_linewidth
+    assert ax.xaxis.get_major_ticks()[0].gridline.get_linestyle() == ":"
+    assert ax.xaxis.get_minor_ticks()[0].gridline.get_linestyle() == def_linestyle
+    assert ax.xaxis.get_major_ticks()[0].gridline.get_alpha() == def_alpha
+    assert ax.xaxis.get_minor_ticks()[0].gridline.get_alpha() == 0.6