From 7d5d5b649c7876425aaa33b15eceeb182e138b2a Mon Sep 17 00:00:00 2001
From: Vikash Kumar <vikashsio793@gmail.com>
Date: Sat, 28 Mar 2026 08:10:13 +0530
Subject: [PATCH 01/12] ENH: Support partial figsize with None (#31400)

---
 lib/matplotlib/figure.py            | 16 ++++++++++++++++
 lib/matplotlib/tests/test_figure.py | 28 ++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/lib/matplotlib/figure.py b/lib/matplotlib/figure.py
index 501b3e32ebf4..b55c85af6417 100644
--- a/lib/matplotlib/figure.py
+++ b/lib/matplotlib/figure.py
@@ -2627,6 +2627,15 @@ def __init__(self,
         frameon = mpl._val_or_rc(frameon, 'figure.frameon')
 
         figsize = _parse_figsize(figsize, dpi)
+        width, height = figsize
+        if width is None and height is None:
+            raise ValueError("Only one of width or height can be None")
+        default_width, default_height = mpl.rcParams["figure.figsize"]
+        if width is None:
+            width = default_width
+        if height is None:
+            height = default_height
+        figsize = (width, height)
 
         if not np.isfinite(figsize).all() or (np.array(figsize) < 0).any():
             raise ValueError('figure size must be positive finite not '
@@ -3155,6 +3164,13 @@ def set_size_inches(self, w, h=None, forward=True):
         """
         if h is None:  # Got called with a single pair as argument.
             w, h = w
+        if w is None and h is None:
+            raise ValueError("Only one of width or height can be None")
+        default_width, default_height = mpl.rcParams["figure.figsize"]
+        if w is None:
+            w = default_width
+        if h is None:
+            h = default_height
         size = np.array([w, h])
         if not np.isfinite(size).all() or (size < 0).any():
             raise ValueError(f'figure size must be positive finite not {size}')
diff --git a/lib/matplotlib/tests/test_figure.py b/lib/matplotlib/tests/test_figure.py
index bb358fa6269f..cd72933a1d82 100644
--- a/lib/matplotlib/tests/test_figure.py
+++ b/lib/matplotlib/tests/test_figure.py
@@ -1883,6 +1883,34 @@ def test_figsize(figsize, figsize_inches):
     assert tuple(fig.get_size_inches()) == figsize_inches
 
 
+def test_figsize_partial_none():
+    default_w, default_h = mpl.rcParams["figure.figsize"]
+
+    fig = plt.figure(figsize=(None, 4))
+    w, h = fig.get_size_inches()
+    assert w == default_w
+    assert h == 4
+    plt.close(fig)
+
+    fig = plt.figure(figsize=(6, None))
+    w, h = fig.get_size_inches()
+    assert w == 6
+    assert h == default_h
+    plt.close(fig)
+
+    fig = plt.figure()
+    fig.set_size_inches(None, 4)
+    w, h = fig.get_size_inches()
+    assert w == default_w
+    assert h == 4
+    plt.close(fig)
+
+
+def test_figsize_both_none():
+    with pytest.raises(ValueError, match="Only one of width or height can be None"):
+        plt.figure(figsize=(None, None))
+
+
 def test_figsize_invalid_unit():
     with pytest.raises(ValueError, match="Invalid unit 'um'"):
         plt.figure(figsize=(6, 4, "um"))

From 1e23dd1b4285405d840e9f848b79664531f51d3f Mon Sep 17 00:00:00 2001
From: Vikash Kumar <vikashsio793@gmail.com>
Date: Sat, 28 Mar 2026 17:56:17 +0530
Subject: [PATCH 02/12] ENH: disallow None in Figure.set_size_inches

---
 lib/matplotlib/figure.py            | 22 +++++++++++++---------
 lib/matplotlib/tests/test_figure.py | 22 +++++++++++++---------
 2 files changed, 26 insertions(+), 18 deletions(-)

diff --git a/lib/matplotlib/figure.py b/lib/matplotlib/figure.py
index b55c85af6417..8b41d64af4d8 100644
--- a/lib/matplotlib/figure.py
+++ b/lib/matplotlib/figure.py
@@ -2629,7 +2629,9 @@ def __init__(self,
         figsize = _parse_figsize(figsize, dpi)
         width, height = figsize
         if width is None and height is None:
-            raise ValueError("Only one of width or height can be None")
+            raise ValueError(
+                "figsize=(None, None) is invalid; at least one of width or "
+                "height must be provided")
         default_width, default_height = mpl.rcParams["figure.figsize"]
         if width is None:
             width = default_width
@@ -3163,14 +3165,16 @@ def set_size_inches(self, w, h=None, forward=True):
         To transform from pixels to inches divide by `Figure.dpi`.
         """
         if h is None:  # Got called with a single pair as argument.
-            w, h = w
-        if w is None and h is None:
-            raise ValueError("Only one of width or height can be None")
-        default_width, default_height = mpl.rcParams["figure.figsize"]
-        if w is None:
-            w = default_width
-        if h is None:
-            h = default_height
+            try:
+                w, h = w
+            except (TypeError, ValueError):
+                raise ValueError(
+                    "Figure.set_size_inches does not accept None; provide "
+                    "both width and height explicitly") from None
+        if w is None or h is None:
+            raise ValueError(
+                "Figure.set_size_inches does not accept None; provide both "
+                "width and height explicitly")
         size = np.array([w, h])
         if not np.isfinite(size).all() or (size < 0).any():
             raise ValueError(f'figure size must be positive finite not {size}')
diff --git a/lib/matplotlib/tests/test_figure.py b/lib/matplotlib/tests/test_figure.py
index cd72933a1d82..e15010eb8f28 100644
--- a/lib/matplotlib/tests/test_figure.py
+++ b/lib/matplotlib/tests/test_figure.py
@@ -1898,19 +1898,23 @@ def test_figsize_partial_none():
     assert h == default_h
     plt.close(fig)
 
-    fig = plt.figure()
-    fig.set_size_inches(None, 4)
-    w, h = fig.get_size_inches()
-    assert w == default_w
-    assert h == 4
-    plt.close(fig)
-
-
 def test_figsize_both_none():
-    with pytest.raises(ValueError, match="Only one of width or height can be None"):
+    with pytest.raises(ValueError,
+                       match=r"figsize=\(None, None\) is invalid"):
         plt.figure(figsize=(None, None))
 
 
+@pytest.mark.parametrize("width, height", [
+    (None, 3),
+    (6, None),
+])
+def test_set_size_inches_rejects_none(width, height):
+    fig = Figure()
+    with pytest.raises(ValueError,
+                       match=r"Figure\.set_size_inches does not accept None"):
+        fig.set_size_inches(width, height)
+
+
 def test_figsize_invalid_unit():
     with pytest.raises(ValueError, match="Invalid unit 'um'"):
         plt.figure(figsize=(6, 4, "um"))

From 3e4ceb56161bf2b8571f4c22bf23e5d2b4d39c96 Mon Sep 17 00:00:00 2001
From: Vikash Kumar <163628932+Vikash-Kumar-23@users.noreply.github.com>
Date: Sun, 29 Mar 2026 19:54:40 +0530
Subject: [PATCH 03/12] Update lib/matplotlib/figure.py

Co-authored-by: Tim Hoffmann <2836374+timhoffm@users.noreply.github.com>
---
 lib/matplotlib/figure.py | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/lib/matplotlib/figure.py b/lib/matplotlib/figure.py
index 8b41d64af4d8..ef90f244df6b 100644
--- a/lib/matplotlib/figure.py
+++ b/lib/matplotlib/figure.py
@@ -3165,16 +3165,6 @@ def set_size_inches(self, w, h=None, forward=True):
         To transform from pixels to inches divide by `Figure.dpi`.
         """
         if h is None:  # Got called with a single pair as argument.
-            try:
-                w, h = w
-            except (TypeError, ValueError):
-                raise ValueError(
-                    "Figure.set_size_inches does not accept None; provide "
-                    "both width and height explicitly") from None
-        if w is None or h is None:
-            raise ValueError(
-                "Figure.set_size_inches does not accept None; provide both "
-                "width and height explicitly")
         size = np.array([w, h])
         if not np.isfinite(size).all() or (size < 0).any():
             raise ValueError(f'figure size must be positive finite not {size}')

From 251786cb8cf207fbfb27cc9df16684941d92e9ec Mon Sep 17 00:00:00 2001
From: Vikash Kumar <163628932+Vikash-Kumar-23@users.noreply.github.com>
Date: Sun, 29 Mar 2026 19:54:52 +0530
Subject: [PATCH 04/12] Update lib/matplotlib/tests/test_figure.py

Co-authored-by: Tim Hoffmann <2836374+timhoffm@users.noreply.github.com>
---
 lib/matplotlib/tests/test_figure.py | 11 -----------
 1 file changed, 11 deletions(-)

diff --git a/lib/matplotlib/tests/test_figure.py b/lib/matplotlib/tests/test_figure.py
index e15010eb8f28..59c778163553 100644
--- a/lib/matplotlib/tests/test_figure.py
+++ b/lib/matplotlib/tests/test_figure.py
@@ -1904,17 +1904,6 @@ def test_figsize_both_none():
         plt.figure(figsize=(None, None))
 
 
-@pytest.mark.parametrize("width, height", [
-    (None, 3),
-    (6, None),
-])
-def test_set_size_inches_rejects_none(width, height):
-    fig = Figure()
-    with pytest.raises(ValueError,
-                       match=r"Figure\.set_size_inches does not accept None"):
-        fig.set_size_inches(width, height)
-
-
 def test_figsize_invalid_unit():
     with pytest.raises(ValueError, match="Invalid unit 'um'"):
         plt.figure(figsize=(6, 4, "um"))

From 42f1478197f780cac0f6269cf9f1c8788440475a Mon Sep 17 00:00:00 2001
From: Vikash Kumar <163628932+Vikash-Kumar-23@users.noreply.github.com>
Date: Sun, 29 Mar 2026 19:55:02 +0530
Subject: [PATCH 05/12] Update lib/matplotlib/tests/test_figure.py

Co-authored-by: Tim Hoffmann <2836374+timhoffm@users.noreply.github.com>
---
 lib/matplotlib/tests/test_figure.py | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/lib/matplotlib/tests/test_figure.py b/lib/matplotlib/tests/test_figure.py
index 59c778163553..bcb8454d5a9e 100644
--- a/lib/matplotlib/tests/test_figure.py
+++ b/lib/matplotlib/tests/test_figure.py
@@ -1888,9 +1888,7 @@ def test_figsize_partial_none():
 
     fig = plt.figure(figsize=(None, 4))
     w, h = fig.get_size_inches()
-    assert w == default_w
-    assert h == 4
-    plt.close(fig)
+    assert w, h == default_w, 4
 
     fig = plt.figure(figsize=(6, None))
     w, h = fig.get_size_inches()

From 9131eea7b89aadb7726180caf34652fc3dc71efc Mon Sep 17 00:00:00 2001
From: Vikash Kumar <163628932+Vikash-Kumar-23@users.noreply.github.com>
Date: Sun, 29 Mar 2026 19:55:13 +0530
Subject: [PATCH 06/12] Update lib/matplotlib/tests/test_figure.py

Co-authored-by: Tim Hoffmann <2836374+timhoffm@users.noreply.github.com>
---
 lib/matplotlib/tests/test_figure.py | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/lib/matplotlib/tests/test_figure.py b/lib/matplotlib/tests/test_figure.py
index bcb8454d5a9e..027f9a09a152 100644
--- a/lib/matplotlib/tests/test_figure.py
+++ b/lib/matplotlib/tests/test_figure.py
@@ -1892,9 +1892,7 @@ def test_figsize_partial_none():
 
     fig = plt.figure(figsize=(6, None))
     w, h = fig.get_size_inches()
-    assert w == 6
-    assert h == default_h
-    plt.close(fig)
+    assert w, h == 6, default_h
 
 def test_figsize_both_none():
     with pytest.raises(ValueError,

From 4e7e12628b52238a70252b260c20535876bfc941 Mon Sep 17 00:00:00 2001
From: Vikash Kumar <vikashsio793@gmail.com>
Date: Sun, 29 Mar 2026 20:24:59 +0530
Subject: [PATCH 07/12] ENH: parse partial None figsize in _parse_figsize

---
 lib/matplotlib/figure.py            | 48 +++++++++++++++++++----------
 lib/matplotlib/tests/test_figure.py |  5 +--
 2 files changed, 34 insertions(+), 19 deletions(-)

diff --git a/lib/matplotlib/figure.py b/lib/matplotlib/figure.py
index ef90f244df6b..63cb8d8610d4 100644
--- a/lib/matplotlib/figure.py
+++ b/lib/matplotlib/figure.py
@@ -2627,17 +2627,6 @@ def __init__(self,
         frameon = mpl._val_or_rc(frameon, 'figure.frameon')
 
         figsize = _parse_figsize(figsize, dpi)
-        width, height = figsize
-        if width is None and height is None:
-            raise ValueError(
-                "figsize=(None, None) is invalid; at least one of width or "
-                "height must be provided")
-        default_width, default_height = mpl.rcParams["figure.figsize"]
-        if width is None:
-            width = default_width
-        if height is None:
-            height = default_height
-        figsize = (width, height)
 
         if not np.isfinite(figsize).all() or (np.array(figsize) < 0).any():
             raise ValueError('figure size must be positive finite not '
@@ -3165,6 +3154,16 @@ def set_size_inches(self, w, h=None, forward=True):
         To transform from pixels to inches divide by `Figure.dpi`.
         """
         if h is None:  # Got called with a single pair as argument.
+            try:
+                w, h = w
+            except (TypeError, ValueError):
+                raise ValueError(
+                    "Figure.set_size_inches does not accept None; provide "
+                    "both width and height explicitly") from None
+        if w is None or h is None:
+            raise ValueError(
+                "Figure.set_size_inches does not accept None; provide both "
+                "width and height explicitly")
         size = np.array([w, h])
         if not np.isfinite(size).all() or (size < 0).any():
             raise ValueError(f'figure size must be positive finite not {size}')
@@ -3773,25 +3772,40 @@ def _parse_figsize(figsize, dpi):
     """
     num_parts = len(figsize)
     if num_parts == 2:
-        return figsize
+        x, y = figsize
     elif num_parts == 3:
         x, y, unit = figsize
         if unit == 'in':
             pass
         elif unit == 'cm':
-            x /= 2.54
-            y /= 2.54
+            if x is not None:
+                x /= 2.54
+            if y is not None:
+                y /= 2.54
         elif unit == 'px':
-            x /= dpi
-            y /= dpi
+            if x is not None:
+                x /= dpi
+            if y is not None:
+                y /= dpi
         else:
             raise ValueError(
                 f"Invalid unit {unit!r} in 'figsize'; "
                 "supported units are 'in', 'cm', 'px'"
             )
-        return x, y
     else:
         raise ValueError(
             "Invalid figsize format, expected (x, y) or (x, y, unit) but got "
             f"{figsize!r}"
         )
+
+    if x is None and y is None:
+        raise ValueError(
+            "figsize=(None, None) is invalid; at least one of width or "
+            "height must be provided")
+
+    default_width, default_height = mpl.rcParams["figure.figsize"]
+    if x is None:
+        x = default_width
+    if y is None:
+        y = default_height
+    return x, y
diff --git a/lib/matplotlib/tests/test_figure.py b/lib/matplotlib/tests/test_figure.py
index 027f9a09a152..0e793a6e7671 100644
--- a/lib/matplotlib/tests/test_figure.py
+++ b/lib/matplotlib/tests/test_figure.py
@@ -1888,11 +1888,12 @@ def test_figsize_partial_none():
 
     fig = plt.figure(figsize=(None, 4))
     w, h = fig.get_size_inches()
-    assert w, h == default_w, 4
+    assert (w, h) == (default_w, 4)
 
     fig = plt.figure(figsize=(6, None))
     w, h = fig.get_size_inches()
-    assert w, h == 6, default_h
+    assert (w, h) == (6, default_h)
+
 
 def test_figsize_both_none():
     with pytest.raises(ValueError,

From be08eaa0a453d9f09d9ba0de87cd63d0ef2dcb79 Mon Sep 17 00:00:00 2001
From: Vikash Kumar <vikashsio793@gmail.com>
Date: Mon, 30 Mar 2026 17:51:53 +0530
Subject: [PATCH 08/12] Simplify set_size_inches argument handling

---
 lib/matplotlib/figure.py | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/lib/matplotlib/figure.py b/lib/matplotlib/figure.py
index 63cb8d8610d4..21f6f8c00fe8 100644
--- a/lib/matplotlib/figure.py
+++ b/lib/matplotlib/figure.py
@@ -3154,12 +3154,7 @@ def set_size_inches(self, w, h=None, forward=True):
         To transform from pixels to inches divide by `Figure.dpi`.
         """
         if h is None:  # Got called with a single pair as argument.
-            try:
-                w, h = w
-            except (TypeError, ValueError):
-                raise ValueError(
-                    "Figure.set_size_inches does not accept None; provide "
-                    "both width and height explicitly") from None
+            w, h = w
         if w is None or h is None:
             raise ValueError(
                 "Figure.set_size_inches does not accept None; provide both "

From 86830f0ea79000d99ff8a56c46418e760c38f0ec Mon Sep 17 00:00:00 2001
From: Vikash Kumar <vikashsio793@gmail.com>
Date: Mon, 30 Mar 2026 18:25:36 +0530
Subject: [PATCH 09/12] DOC: document partial None support for figsize

---
 doc/release/next_whats_new/partial_figsize_none.rst | 12 ++++++++++++
 lib/matplotlib/figure.py                            |  4 ++++
 lib/matplotlib/pyplot.py                            |  4 ++++
 3 files changed, 20 insertions(+)
 create mode 100644 doc/release/next_whats_new/partial_figsize_none.rst

diff --git a/doc/release/next_whats_new/partial_figsize_none.rst b/doc/release/next_whats_new/partial_figsize_none.rst
new file mode 100644
index 000000000000..37c3c9b2f547
--- /dev/null
+++ b/doc/release/next_whats_new/partial_figsize_none.rst
@@ -0,0 +1,12 @@
+Partial ``None`` support for ``figsize`` at figure creation
+------------------------------------------------------------
+
+Figure creation now accepts a single ``None`` in ``figsize``.
+Passing ``(None, h)`` uses the default width from :rc:`figure.figsize`, and
+passing ``(w, None)`` uses the default height.
+Passing ``(None, None)`` is invalid and raises a `ValueError`.
+
+For example::
+
+    import matplotlib.pyplot as plt
+    fig = plt.figure(figsize=(None, 4))
diff --git a/lib/matplotlib/figure.py b/lib/matplotlib/figure.py
index 21f6f8c00fe8..29c10c51fef3 100644
--- a/lib/matplotlib/figure.py
+++ b/lib/matplotlib/figure.py
@@ -2492,6 +2492,10 @@ def __init__(self,
             - a tuple ``(width, height)``, which is interpreted in inches, i.e. as
               ``(width, height, "in")``.
 
+            One of *width* or *height* may be ``None``; the missing value is
+            taken from :rc:`figure.figsize`. Passing ``(None, None)`` is not
+            allowed and raises a `ValueError`.
+
         dpi : float, default: :rc:`figure.dpi`
             Dots per inch.
 
diff --git a/lib/matplotlib/pyplot.py b/lib/matplotlib/pyplot.py
index 483bc031336c..014f0696b43d 100644
--- a/lib/matplotlib/pyplot.py
+++ b/lib/matplotlib/pyplot.py
@@ -947,6 +947,10 @@ def figure(
           "px".
         - a tuple ``(x, y)``, which is interpreted as ``(x, y, "inch")``.
 
+        One of *width* or *height* may be ``None``; the missing value is taken
+        from :rc:`figure.figsize`. Passing ``(None, None)`` is not allowed and
+        raises a `ValueError`.
+
     dpi : float, default: :rc:`figure.dpi`
         The resolution of the figure in dots-per-inch.
 

From d731bd44d93c1287a2b6a21d034d7cccfd56f492 Mon Sep 17 00:00:00 2001
From: Vikash Kumar <163628932+Vikash-Kumar-23@users.noreply.github.com>
Date: Tue, 31 Mar 2026 05:35:34 +0530
Subject: [PATCH 10/12] Update
 doc/release/next_whats_new/partial_figsize_none.rst

Co-authored-by: Tim Hoffmann <2836374+timhoffm@users.noreply.github.com>
---
 doc/release/next_whats_new/partial_figsize_none.rst | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/doc/release/next_whats_new/partial_figsize_none.rst b/doc/release/next_whats_new/partial_figsize_none.rst
index 37c3c9b2f547..43bd3e34cc73 100644
--- a/doc/release/next_whats_new/partial_figsize_none.rst
+++ b/doc/release/next_whats_new/partial_figsize_none.rst
@@ -1,5 +1,5 @@
-Partial ``None`` support for ``figsize`` at figure creation
-------------------------------------------------------------
+Partial ``figsize`` specification at figure creation
+----------------------------------------------------
 
 Figure creation now accepts a single ``None`` in ``figsize``.
 Passing ``(None, h)`` uses the default width from :rc:`figure.figsize`, and

From cf868b9820eee3ff9b176e89a379875723cec4cf Mon Sep 17 00:00:00 2001
From: Vikash Kumar <163628932+Vikash-Kumar-23@users.noreply.github.com>
Date: Tue, 31 Mar 2026 05:35:53 +0530
Subject: [PATCH 11/12] Update lib/matplotlib/figure.py

Co-authored-by: Tim Hoffmann <2836374+timhoffm@users.noreply.github.com>
---
 lib/matplotlib/figure.py | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/lib/matplotlib/figure.py b/lib/matplotlib/figure.py
index 29c10c51fef3..ad0206e0db5c 100644
--- a/lib/matplotlib/figure.py
+++ b/lib/matplotlib/figure.py
@@ -2492,9 +2492,8 @@ def __init__(self,
             - a tuple ``(width, height)``, which is interpreted in inches, i.e. as
               ``(width, height, "in")``.
 
-            One of *width* or *height* may be ``None``; the missing value is
-            taken from :rc:`figure.figsize`. Passing ``(None, None)`` is not
-            allowed and raises a `ValueError`.
+            One of *width* or *height* may be ``None``; the respective value is
+            taken from :rc:`figure.figsize`.
 
         dpi : float, default: :rc:`figure.dpi`
             Dots per inch.

From c1653cffde70916599fcf2b6bb0a66fdad213303 Mon Sep 17 00:00:00 2001
From: Vikash Kumar <163628932+Vikash-Kumar-23@users.noreply.github.com>
Date: Tue, 31 Mar 2026 05:36:11 +0530
Subject: [PATCH 12/12] Update lib/matplotlib/pyplot.py

Co-authored-by: Tim Hoffmann <2836374+timhoffm@users.noreply.github.com>
---
 lib/matplotlib/pyplot.py | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/lib/matplotlib/pyplot.py b/lib/matplotlib/pyplot.py
index 014f0696b43d..ed7821ca1b27 100644
--- a/lib/matplotlib/pyplot.py
+++ b/lib/matplotlib/pyplot.py
@@ -947,9 +947,8 @@ def figure(
           "px".
         - a tuple ``(x, y)``, which is interpreted as ``(x, y, "inch")``.
 
-        One of *width* or *height* may be ``None``; the missing value is taken
-        from :rc:`figure.figsize`. Passing ``(None, None)`` is not allowed and
-        raises a `ValueError`.
+        One of *width* or *height* may be ``None``; the respective value is taken
+        from :rc:`figure.figsize`.
 
     dpi : float, default: :rc:`figure.dpi`
         The resolution of the figure in dots-per-inch.