env: only import packaging wherever required

PR #395

Co-authored-by: Ravi Teja Gannavarapu <raviteja@clevertap.com>

src/build/env.py

@@ -15,9 +15,6 @@
 from types import TracebackType
 from typing import Callable, Iterable, List, Optional, Tuple, Type
 
-import packaging.requirements
-import packaging.version
-
 import build
 
 
@@ -62,6 +59,8 @@ def install(self, requirements: Iterable[str]) -> None:
 
 @functools.lru_cache(maxsize=None)
 def _should_use_virtualenv() -> bool:
+    import packaging.requirements
+
     # virtualenv might be incompatible if it was installed separately
     # from build. This verifies that virtualenv and all of its
     # dependencies are installed as specified by build.
@@ -254,6 +253,8 @@ def _create_isolated_env_venv(path: str) -> Tuple[str, str]:
     """
     import venv
 
+    import packaging.version
+
     venv.EnvBuilder(with_pip=True, symlinks=_fs_supports_symlink()).create(path)
     executable, script_dir, purelib = _find_executable_and_scripts(path)
 

tests/test_env.py

@@ -112,7 +112,7 @@ def test_isolated_env_log(mocker, caplog, package_test_flit):
         ('INFO', 'Installing packages in isolated environment... (something)'),
     ]
     if sys.version_info >= (3, 8):  # stacklevel
-        assert [(record.lineno) for record in caplog.records] == [105, 103, 194]
+        assert [(record.lineno) for record in caplog.records] == [105, 102, 193]
 
 
 @pytest.mark.isolated