validators: avoid urllib.request at import-time

jsonschema/benchmarks/import_benchmark.py

@@ -0,0 +1,31 @@
+"""
+A benchmark which measures the import time of jsonschema
+"""
+
+import subprocess
+import sys
+
+
+def import_time(loops):
+    total_us = 0
+    for _ in range(loops):
+        p = subprocess.run(  # noqa: S603 (arguments are static)
+            [sys.executable, "-X", "importtime", "-c", "import jsonschema"],
+            stderr=subprocess.PIPE,
+            stdout=subprocess.DEVNULL,
+            check=True,
+        )
+
+        line = p.stderr.splitlines()[-1]
+        field = line.split(b"|")[-2].strip()
+        us = int(field)  # microseconds
+        total_us += us
+
+    # pyperf expects seconds
+    return total_us / 1_000_000.0
+
+if __name__ == "__main__":
+    from pyperf import Runner
+    runner = Runner()
+
+    runner.bench_time_func("Import time (cumulative)", import_time)

jsonschema/tests/test_validators.py

@@ -2379,11 +2379,9 @@ def fake_urlopen(url):
             self.assertEqual(url, "http://bar")
             yield BytesIO(json.dumps(schema).encode("utf8"))
 
-        self.addCleanup(setattr, validators, "urlopen", validators.urlopen)
-        validators.urlopen = fake_urlopen
-
-        with self.resolver.resolving(ref) as resolved:
-            pass
+        with mock.patch("urllib.request.urlopen", new=fake_urlopen):  # noqa: SIM117
+            with self.resolver.resolving(ref) as resolved:
+                pass
         self.assertEqual(resolved, 12)
 
     def test_it_retrieves_local_refs_via_urlopen(self):

jsonschema/validators.py

@@ -9,7 +9,6 @@
 from operator import methodcaller
 from typing import TYPE_CHECKING
 from urllib.parse import unquote, urldefrag, urljoin, urlsplit
-from urllib.request import urlopen
 from warnings import warn
 import contextlib
 import json
@@ -1225,6 +1224,7 @@ def resolve_remote(self, uri):
             result = requests.get(uri).json()
         else:
             # Otherwise, pass off to urllib and assume utf-8
+            from urllib.request import urlopen
             with urlopen(uri) as url:  # noqa: S310
                 result = json.loads(url.read().decode("utf-8"))