feat: select matplotlib inline backend by default in server

We do this by checking if the env var 'MPLBACKEND' is not set, and if so, we set it to
module://matplotlib_inline.backend_inline

solara/components/matplotlib.py

@@ -34,8 +34,7 @@ def Page():
     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.
 
-    If you still must use pyplot to create the figure, make sure you call `plt.switch_backend("agg")`
-    before creating the figure, to avoid starting an interactive backend.
+    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.

solara/server/patch.py

@@ -1,4 +1,5 @@
 import logging
+import os
 import pdb
 import sys
 import threading
@@ -25,6 +26,7 @@
 if patch_display is not None and sys.platform != "emscripten":
     patch_display()
 ipywidget_version_major = int(ipywidgets.__version__.split(".")[0])
+ipykernel_version_major = int(ipykernel.__version__.split(".")[0])
 
 
 class FakeIPython:
@@ -331,6 +333,13 @@ def patch():
     else:
         patch_ipyreact()
 
+    if "MPLBACKEND" not in os.environ:
+        if ipykernel_version_major < 6:
+            # changed in https://github.com/ipython/ipykernel/pull/591
+            os.environ["MPLBACKEND"] = "ipykernel.pylab.backend_inline"
+        else:
+            os.environ["MPLBACKEND"] = "module://matplotlib_inline.backend_inline"
+
     # the ipyvue.Template module cannot be accessed like ipyvue.Template
     # because the import in ipvue overrides it
     template_mod = sys.modules["ipyvue.Template"]

solara/website/components/notebook.py

@@ -11,11 +11,6 @@
 import solara.toestand
 from solara.components.markdown import ExceptionGuard
 
-if solara._using_solara_server():
-    from matplotlib import pyplot as plt
-
-    plt.switch_backend("agg")
-
 HERE = Path(__file__).parent
 
 

solara/website/pages/examples/general/live_update.py

@@ -5,9 +5,6 @@
 
 import solara
 
-# ensure that an interactive backend doesn't start when plotting with matplotlib
-plt.switch_backend("agg")
-
 
 @solara.component
 def Page():