Use env variable to configure matplotlib backend

e2e_playwright/lazy_loaded_modules.py

@@ -24,6 +24,7 @@
     "altair",
     "graphviz",
     "watchdog",
+    "matplotlib",
     "pandas",
     "pyarrow",
     "streamlit.emojis",
@@ -33,7 +34,6 @@
     # TODO(lukasmasuch): Lazy load more packages:
     # "streamlit.hello",
     # "numpy",
-    # "matplotlib",
     # "plotly",
     # "pillow",
 ]

e2e_playwright/lazy_loaded_modules_test.py

@@ -20,6 +20,6 @@
 def test_lazy_loaded_modules_are_not_imported(app: Page):
     """Test that lazy loaded modules are not imported when the page is loaded."""
     markdown_elements = app.get_by_test_id("stMarkdown")
-    expect(markdown_elements).to_have_count(13)
+    expect(markdown_elements).to_have_count(14)
     for element in markdown_elements.all():
         expect(element).to_have_text(re.compile(r".*not loaded.*"))

lib/streamlit/__init__.py

@@ -44,6 +44,18 @@
 
 # IMPORTANT: Prefix with an underscore anything that the user shouldn't see.
 
+
+# Set Matplotlib backend to avoid a crash.
+# The default Matplotlib backend crashes Python on OSX when run on a thread
+# that's not the main thread, so here we set a safer backend as a fix.
+# This fix is OS-independent. We didn't see a good reason to make this
+# Mac-only. Consistency within Streamlit seemed more important.
+# This needs to run before any other import of matplotlib could happen.
+import os as _os
+
+_os.environ["MPLBACKEND"] = "Agg"
+
+
 # Must be at the top, to avoid circular dependency.
 from streamlit import logger as _logger
 from streamlit import config as _config

lib/streamlit/testing/v1/app_test.py

@@ -82,12 +82,9 @@
 )
 from streamlit.testing.v1.local_script_runner import LocalScriptRunner
 from streamlit.util import HASHLIB_KWARGS
-from streamlit.web.bootstrap import _fix_matplotlib_crash
 
 TMP_DIR = tempfile.TemporaryDirectory()
 
-_fix_matplotlib_crash()
-
 
 class AppTest:
     """

lib/streamlit/web/bootstrap.py

@@ -12,13 +12,16 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from __future__ import annotations
+
 import asyncio
 import os
 import signal
 import sys
 from pathlib import Path
-from typing import Any, Dict, List
+from typing import Any, Dict, Final, List
 
+# TODO(lukasmasuch): Lazy-load this module:
 import click
 
 from streamlit import (
@@ -38,9 +41,9 @@
 from streamlit.watcher import report_watchdog_availability, watch_dir, watch_file
 from streamlit.web.server import Server, server_address_is_unix_socket, server_util
 
-LOGGER = get_logger(__name__)
+_LOGGER: Final = get_logger(__name__)
 
-NEW_VERSION_TEXT = """
+NEW_VERSION_TEXT: Final = """
   %(new_version)s
 
   See what's new at https://discuss.streamlit.io/c/announcements
@@ -62,7 +65,7 @@
 
 
 def _set_up_signal_handler(server: Server) -> None:
-    LOGGER.debug("Setting up signal handler")
+    _LOGGER.debug("Setting up signal handler")
 
     def signal_handler(signal_number, stack_frame):
         # The server will shut down its threads and exit its loop.
@@ -85,35 +88,6 @@ def _fix_sys_path(main_script_path: str) -> None:
     sys.path.insert(0, os.path.dirname(main_script_path))
 
 
-def _fix_matplotlib_crash() -> None:
-    """Set Matplotlib backend to avoid a crash.
-
-    The default Matplotlib backend crashes Python on OSX when run on a thread
-    that's not the main thread, so here we set a safer backend as a fix.
-    Users can always disable this behavior by setting the config
-    runner.fixMatplotlib = false.
-
-    This fix is OS-independent. We didn't see a good reason to make this
-    Mac-only. Consistency within Streamlit seemed more important.
-    """
-    if config.get_option("runner.fixMatplotlib"):
-        try:
-            # TODO: a better option may be to set
-            #  os.environ["MPLBACKEND"] = "Agg". We'd need to do this towards
-            #  the top of __init__.py, before importing anything that imports
-            #  pandas (which imports matplotlib). Alternately, we could set
-            #  this environment variable in a new entrypoint defined in
-            #  setup.py. Both of these introduce additional trickiness: they
-            #  need to run without consulting streamlit.config.get_option,
-            #  because this would import streamlit, and therefore matplotlib.
-            import matplotlib
-
-            matplotlib.use("Agg")
-        except ImportError:
-            # Matplotlib is not installed. No need to do anything.
-            pass
-
-
 def _fix_tornado_crash() -> None:
     """Set default asyncio policy to be compatible with Tornado 6.
 
@@ -168,7 +142,7 @@ def _on_server_start(server: Server) -> None:
     try:
         secrets.load_if_toml_exists()
     except Exception as ex:
-        LOGGER.error(f"Failed to load secrets.toml file", exc_info=ex)
+        _LOGGER.error(f"Failed to load secrets.toml file", exc_info=ex)
 
     def maybe_open_browser():
         if config.get_option("server.headless"):
@@ -402,7 +376,6 @@ def run(
     This starts a blocking asyncio eventloop.
     """
     _fix_sys_path(main_script_path)
-    _fix_matplotlib_crash()
     _fix_tornado_crash()
     _fix_sys_argv(main_script_path, args)
     _fix_pydeck_mapbox_api_warning()

lib/tests/streamlit/streamlit_test.py

@@ -21,6 +21,8 @@
 import tempfile
 import unittest
 
+import matplotlib
+
 import streamlit as st
 from streamlit import __version__
 
@@ -48,6 +50,25 @@ def test_get_option(self):
         # This is set in lib/tests/conftest.py to False
         self.assertEqual(False, st.get_option("browser.gatherUsageStats"))
 
+    def test_matplotlib_uses_agg(self):
+        """Test that Streamlit uses the 'Agg' backend for matplotlib."""
+        ORIG_PLATFORM = sys.platform
+
+        for platform in ["darwin", "linux2"]:
+            sys.platform = platform
+
+            self.assertEqual(matplotlib.get_backend().lower(), "agg")
+            self.assertEqual(os.environ.get("MPLBACKEND").lower(), "agg")
+
+            # Force matplotlib to use a different backend
+            matplotlib.use("pdf", force=True)
+            self.assertEqual(matplotlib.get_backend().lower(), "pdf")
+
+            # Reset the backend to 'Agg'
+            matplotlib.use("agg", force=True)
+            self.assertEqual(matplotlib.get_backend().lower(), "agg")
+        sys.platform = ORIG_PLATFORM
+
     def test_public_api(self):
         """Test that we don't accidentally remove (or add) symbols
         to the public `st` API.

lib/tests/streamlit/web/bootstrap_test.py

@@ -18,7 +18,6 @@
 from unittest import IsolatedAsyncioTestCase
 from unittest.mock import Mock, patch
 
-import matplotlib
 import pytest
 
 from streamlit import config
@@ -31,27 +30,6 @@
 from tests.testutil import patch_config_options, should_skip_pydantic_tests
 
 
-class BootstrapTest(unittest.TestCase):
-    @patch("streamlit.web.bootstrap.asyncio.run", Mock())
-    @patch("streamlit.web.bootstrap.Server", Mock())
-    @patch("streamlit.web.bootstrap._install_pages_watcher", Mock())
-    def test_fix_matplotlib_crash(self):
-        """Test that bootstrap.run sets the matplotlib backend to
-        "Agg".
-        """
-        # TODO: Find a proper way to mock sys.platform
-        ORIG_PLATFORM = sys.platform
-
-        for platform in ["darwin", "linux2"]:
-            sys.platform = platform
-
-            matplotlib.use("pdf", force=True)
-            bootstrap.run("/not/a/script", "", [], {})
-            self.assertEqual("agg", matplotlib.get_backend().lower())
-
-        sys.platform = ORIG_PLATFORM
-
-
 class BootstrapPydanticFixTest(unittest.TestCase):
     def pydantic_model_definition(self):
         from pydantic import BaseModel, root_validator, validator
@@ -451,7 +429,7 @@ def test_load_secrets(self, mock_load_secrets):
 
     @patch("streamlit.web.bootstrap.asyncio.get_running_loop", Mock())
     @patch("streamlit.web.bootstrap._maybe_print_static_folder_warning", Mock())
-    @patch("streamlit.web.bootstrap.LOGGER.error")
+    @patch("streamlit.web.bootstrap._LOGGER.error")
     @patch("streamlit.web.bootstrap.secrets.load_if_toml_exists")
     def test_log_secret_load_error(self, mock_load_secrets, mock_log_error):
         """If secrets throws an error on startup, we catch and log it."""