feat: support matplotlib pylab interface in solara server

This makes code that 'just works' in the notebook also work in solara
server.

solara/components/matplotlib.py

@@ -14,31 +14,44 @@ def FigureMatplotlib(
 ):
     """Display a matplotlib figure.
 
-    We recomment not to use the pyplot interface, but rather to create a figure directly, e.g:
 
-    ```python
-    import reacton
-    import solara as sol
+    ## Example
+
+    ```solara
+    import solara
     from matplotlib.figure import Figure
 
     @solara.component
     def Page():
-        # do this instead of plt.figure()
         fig = Figure()
         ax = fig.subplots()
         ax.plot([1, 2, 3], [1, 4, 9])
         return solara.FigureMatplotlib(fig)
-
     ```
 
-    You should also avoid drawing using the pyplot interface, as it is not thread-safe. If you do use it,
-    your drawing might be corrupted due to another thread/user drawing at the same time.
-
     When running under solara-server, we by default configure the same 'inline' backend as in the Jupyter notebook.
 
     For performance reasons, you might want to pass in a list of dependencies that indicate when
     the figure changed, to avoid re-rendering it on every render.
 
+    ## Example using pyplot
+
+    Note that it is also possible to use the pyplot interface, but be sure to close the figure not to leak memory.
+
+    ```solara
+    import solara
+    import matplotlib.pyplot as plt
+
+    @solara.component
+    def Page():
+        plt.figure()
+        plt.plot([1, 2, 3], [1, 4, 9])
+        plt.show()
+        plt.close()
+    ```
+
+    Note that the figure is not the same size using the pyplot interface, due to the default figure size being different.
+
 
     ## Arguments
 

solara/server/app.py

@@ -15,7 +15,7 @@
 
 import solara
 
-from . import kernel_context, reload, settings
+from . import kernel_context, patch, reload, settings
 from .kernel import Kernel
 from .utils import pdb_guard
 
@@ -68,6 +68,9 @@ def __init__(self, name, default_app_name="Page"):
         with dummy_kernel_context:
             app = self._execute()
 
+        # We now ran the app, now we can check for patches that require heavy imports
+        patch.patch_heavy_imports()
+
         self._first_execute_app = app
         reload.reloader.root_path = self.directory
         if self.type == AppType.MODULE:
@@ -198,6 +201,9 @@ def run(self):
                     self._first_execute_app = None
                     self._first_execute_app = self._execute()
                     print("Re-executed app", self.name)  # noqa
+                    # We now ran the app again, might contain new imports
+                    patch.patch_heavy_imports()
+
         return self._first_execute_app
 
     def on_file_change(self, name):

solara/server/patch.py

@@ -1,3 +1,4 @@
+import functools
 import logging
 import os
 import pdb
@@ -198,6 +199,16 @@ def __len__(self):
     def __setitem__(self, key, value):
         self._get_context_dict().__setitem__(key, value)
 
+    # support OrderedDict API for matplotlib
+    def move_to_end(self, key, last=True):
+        assert last, "only last=True is supported"
+        item = self.pop(key)
+        self[key] = item
+
+    # matplotlib assumes .values() returns a list
+    def values(self):
+        return list(self._get_context_dict().values())
+
 
 class context_dict_widgets(context_dict):
     def _get_context_dict(self) -> dict:
@@ -315,6 +326,42 @@ def patch_ipyreact():
     ipyreact.importmap._update_import_map = lambda: None
 
 
+def once(f):
+    called = False
+    return_value = None
+
+    @functools.wraps(f)
+    def wrapper():
+        nonlocal called
+        nonlocal return_value
+        if called:
+            return return_value
+        called = True
+        return_value = f()
+        return return_value
+
+    return wrapper
+
+
+@once
+def patch_matplotlib():
+    import matplotlib._pylab_helpers
+
+    prev = matplotlib._pylab_helpers.Gcf.figs
+    matplotlib._pylab_helpers.Gcf.figs = context_dict_user("matplotlib.pylab.figure_managers", prev)  # type: ignore
+
+    def cleanup():
+        matplotlib._pylab_helpers.Gcf.figs = prev
+
+    return cleanup
+
+
+def patch_heavy_imports():
+    # patches that we only want to do if a package is imported, because they may slow down startup
+    if "matplotlib" in sys.modules:
+        patch_matplotlib()
+
+
 def patch():
     global _patched
     global global_widgets_dict

tests/unit/matplotlib_test.py

@@ -1,6 +1,9 @@
-import solara
 from matplotlib.figure import Figure
 
+import solara
+import solara.server.patch
+from solara.server import kernel
+
 
 @solara.component
 def Page():
@@ -14,3 +17,36 @@ def Page():
 def test_render():
     box, rc = solara.render(Page(), handle_error=False)
     assert len(box.children) == 1
+
+
+def test_pylab(no_kernel_context):
+    cleanup = solara.server.patch.patch_matplotlib()
+    try:
+        kernel_1 = kernel.Kernel()
+        context_1 = solara.server.kernel_context.VirtualKernelContext(id="1", kernel=kernel_1, session_id="session-1")
+        kernel_2 = kernel.Kernel()
+        context_2 = solara.server.kernel_context.VirtualKernelContext(id="2", kernel=kernel_2, session_id="session-1")
+        import matplotlib.pyplot as plt
+        from matplotlib._pylab_helpers import Gcf
+
+        assert len(Gcf.get_all_fig_managers()) == 0
+        plt.figure()
+        assert len(Gcf.get_all_fig_managers()) == 1
+        with context_1:
+            assert len(Gcf.get_all_fig_managers()) == 0
+            plt.figure()
+            assert len(Gcf.get_all_fig_managers()) == 1
+        assert len(Gcf.get_all_fig_managers()) == 1
+        with context_2:
+            assert len(Gcf.get_all_fig_managers()) == 0
+            plt.figure()
+            assert len(Gcf.get_all_fig_managers()) == 1
+            plt.figure()
+            assert len(Gcf.get_all_fig_managers()) == 2
+        with context_1:
+            assert len(Gcf.get_all_fig_managers()) == 1
+
+    finally:
+        cleanup()
+        context_1.close()
+        context_2.close()