cache extract_lambda_source

hypothesis-python/RELEASE.rst

@@ -0,0 +1,3 @@
+RELEASE_TYPE: patch
+
+This patch fixes a significant slowdown when using the :func:`~hypothesis.stateful.precondition` decorator in some cases, due to expensive repr formatting internally (:issue:`3963`).

hypothesis-python/src/hypothesis/internal/reflection.py

@@ -21,7 +21,7 @@
 import textwrap
 import types
 import warnings
-from functools import partial, wraps
+from functools import lru_cache, partial, wraps
 from io import StringIO
 from keyword import iskeyword
 from random import _inst as global_random_instance
@@ -303,6 +303,7 @@ def visit_Lambda(self, node):
 SPACE_PRECEDES_CLOSE_BRACKET = re.compile(r" \)")
 
 
+@lru_cache(maxsize=1024)
 def extract_lambda_source(f):
     """Extracts a single lambda expression from the string source. Returns a
     string indicating an unknown body if it gets confused in any way.

hypothesis-python/tests/cover/test_reflection.py

@@ -541,12 +541,10 @@ def test_required_args(target, args, kwargs, expected):
     assert required_args(target, args, kwargs) == expected
 
 
-# fmt: off
-pi = "π"; is_str_pi = lambda x: x == pi  # noqa: E702
-# fmt: on
-
-
 def test_can_handle_unicode_identifier_in_same_line_as_lambda_def():
+    # fmt: off
+    pi = "π"; is_str_pi = lambda x: x == pi  # noqa: E702
+    # fmt: on
     assert get_pretty_function_description(is_str_pi) == "lambda x: x == pi"
 
 
@@ -567,6 +565,9 @@ def test_does_not_crash_on_utf8_lambda_without_encoding(monkeypatch):
     # has to fall back to assuming it's ASCII.
 
     monkeypatch.setattr(reflection, "detect_encoding", None)
+    # fmt: off
+    pi = "π"; is_str_pi = lambda x: x == pi  # noqa: E702
+    # fmt: on
     assert get_pretty_function_description(is_str_pi) == "lambda x: <unknown>"