fix: dont use mpl backend when running as a script (#1089)

* fix: dont use mpl backend when running as script

* add bugs smoke

marimo/_output/formatters/matplotlib_formatters.py

@@ -13,12 +13,16 @@ def package_name() -> str:
     def register(self) -> None:
         import matplotlib  # type: ignore
 
-        from marimo._runtime.context import get_global_context
+        from marimo._runtime.context import (
+            get_global_context,
+            runtime_context_installed,
+        )
 
         get_global_context().set_mpl_installed(True)
         from marimo._output import mpl  # noqa: F401
 
-        matplotlib.use("module://marimo._output.mpl")
+        if runtime_context_installed():
+            matplotlib.use("module://marimo._output.mpl")
 
         import base64
         import io

marimo/_runtime/context.py

@@ -141,3 +141,12 @@ def get_context() -> RuntimeContext:
     if _THREAD_LOCAL_CONTEXT.runtime_context is None:
         raise ContextNotInitializedError
     return _THREAD_LOCAL_CONTEXT.runtime_context
+
+
+def runtime_context_installed() -> bool:
+    try:
+        get_context()
+    except ContextNotInitializedError:
+        return False
+    else:
+        return True

marimo/_smoke_tests/bugs/1086.py

@@ -0,0 +1,21 @@
+# Copyright 2024 Marimo. All rights reserved.
+import marimo
+
+__generated_with = "0.3.10"
+app = marimo.App()
+
+
+@app.cell
+def __():
+    import matplotlib.pyplot as plt
+    import numpy as np
+
+    plt.plot(np.arange(52))
+
+    # better to do plt.gca(), but discovered this translating script
+    plt.show()
+    return np, plt
+
+
+if __name__ == "__main__":
+    app.run()