BLD: Lazy load f2py test utilities

These are only used during testing. It's fine to load it while running the test
because actually running the test can't be done while cross compiling.

Part of changes to support #17620 to prevent importing numpy during builds to support cross-compilation

1 files changed, 30 insertions, 4 deletions

diff --git a/numpy/f2py/__init__.py b/numpy/f2py/__init__.py
index 949bac0ff..328045c07 100644
--- a/numpy/f2py/__init__.py
+++ b/numpy/f2py/__init__.py
@@ -9,7 +9,6 @@ import subprocess
 import os
 
 from . import f2py2e
-from . import f2py_testing
 from . import diagnose
 
 run_main = f2py2e.run_main
@@ -113,6 +112,33 @@ def compile(source,
             os.remove(fname)
     return status
 
-from numpy._pytesttester import PytestTester
-test = PytestTester(__name__)
-del PytestTester
+
+if sys.version_info[:2] >= (3, 7):
+    # module level getattr is only supported in 3.7 onwards
+    # https://www.python.org/dev/peps/pep-0562/
+    def __getattr__(attr):
+
+        # Avoid importing things that aren't needed for building
+        # which might import the main numpy module
+        if attr == "f2py_testing":
+            import numpy.f2py.f2py_testing as f2py_testing
+            return f2py_testing
+
+        elif attr == "test":
+            from numpy._pytesttester import PytestTester
+            test = PytestTester(__name__)
+            return test
+
+        else:
+            raise AttributeError("module {!r} has no attribute "
+                                 "{!r}".format(__name__, attr))
+
+    def __dir__():
+        return list(globals().keys() | {"f2py_testing", "test"})
+
+else:
+    from . import f2py_testing
+
+    from numpy._pytesttester import PytestTester
+    test = PytestTester(__name__)
+    del PytestTester