Avoid importing IPython if notebook cells do not contain magics

CHANGES.md

@@ -30,6 +30,8 @@
 
 <!-- Changes that improve Black's performance. -->
 
+- Avoid importing `IPython` if notebook cells do not contain magics (#3782)
+
 ### Output
 
 <!-- Changes to Black's terminal output and error messages -->

src/black/__init__.py

@@ -668,7 +668,7 @@ def get_sources(
                 p = Path(f"{STDIN_PLACEHOLDER}{str(p)}")
 
             if p.suffix == ".ipynb" and not jupyter_dependencies_are_installed(
-                verbose=verbose, quiet=quiet
+                warn=verbose or not quiet
             ):
                 continue
 

src/black/files.py

@@ -384,7 +384,7 @@ def gen_python_files(
 
         elif child.is_file():
             if child.suffix == ".ipynb" and not jupyter_dependencies_are_installed(
-                verbose=verbose, quiet=quiet
+                warn=verbose or not quiet
             ):
                 continue
             include_match = include.search(normalized_path) if include else True

src/black/handle_ipynb_magics.py

@@ -6,6 +6,7 @@
 import secrets
 import sys
 from functools import lru_cache
+from importlib.util import find_spec
 from typing import Dict, List, Optional, Tuple
 
 if sys.version_info >= (3, 10):
@@ -56,25 +57,17 @@ class Replacement:
 
 
 @lru_cache
-def jupyter_dependencies_are_installed(*, verbose: bool, quiet: bool) -> bool:
-    try:
-        # isort: off
-        # tokenize_rt is less commonly installed than IPython
-        # and IPython is expensive to import
-        import tokenize_rt  # noqa:F401
-        import IPython  # noqa:F401
-
-        # isort: on
-    except ModuleNotFoundError:
-        if verbose or not quiet:
-            msg = (
-                "Skipping .ipynb files as Jupyter dependencies are not installed.\n"
-                'You can fix this by running ``pip install "black[jupyter]"``'
-            )
-            out(msg)
-        return False
-    else:
-        return True
+def jupyter_dependencies_are_installed(*, warn: bool) -> bool:
+    installed = (
+        find_spec("tokenize_rt") is not None and find_spec("IPython") is not None
+    )
+    if not installed and warn:
+        msg = (
+            "Skipping .ipynb files as Jupyter dependencies are not installed.\n"
+            'You can fix this by running ``pip install "black[jupyter]"``'
+        )
+        out(msg)
+    return installed
 
 
 def remove_trailing_semicolon(src: str) -> Tuple[str, bool]:

tests/test_ipynb.py

@@ -440,17 +440,13 @@ def test_cache_isnt_written_if_no_jupyter_deps_single(
     nb = get_case_path("jupyter", "notebook_trailing_newline.ipynb")
     tmp_nb = tmp_path / "notebook.ipynb"
     tmp_nb.write_bytes(nb.read_bytes())
-    monkeypatch.setattr(
-        "black.jupyter_dependencies_are_installed", lambda verbose, quiet: False
-    )
+    monkeypatch.setattr("black.jupyter_dependencies_are_installed", lambda warn: False)
     result = runner.invoke(
         main, [str(tmp_path / "notebook.ipynb"), f"--config={EMPTY_CONFIG}"]
     )
     assert "No Python files are present to be formatted. Nothing to do" in result.output
     jupyter_dependencies_are_installed.cache_clear()
-    monkeypatch.setattr(
-        "black.jupyter_dependencies_are_installed", lambda verbose, quiet: True
-    )
+    monkeypatch.setattr("black.jupyter_dependencies_are_installed", lambda warn: True)
     result = runner.invoke(
         main, [str(tmp_path / "notebook.ipynb"), f"--config={EMPTY_CONFIG}"]
     )
@@ -466,13 +462,13 @@ def test_cache_isnt_written_if_no_jupyter_deps_dir(
     tmp_nb = tmp_path / "notebook.ipynb"
     tmp_nb.write_bytes(nb.read_bytes())
     monkeypatch.setattr(
-        "black.files.jupyter_dependencies_are_installed", lambda verbose, quiet: False
+        "black.files.jupyter_dependencies_are_installed", lambda warn: False
     )
     result = runner.invoke(main, [str(tmp_path), f"--config={EMPTY_CONFIG}"])
     assert "No Python files are present to be formatted. Nothing to do" in result.output
     jupyter_dependencies_are_installed.cache_clear()
     monkeypatch.setattr(
-        "black.files.jupyter_dependencies_are_installed", lambda verbose, quiet: True
+        "black.files.jupyter_dependencies_are_installed", lambda warn: True
     )
     result = runner.invoke(main, [str(tmp_path), f"--config={EMPTY_CONFIG}"])
     assert "reformatted" in result.output