ENH: add `numpy.f2py.get_include` function

This is useful for similar reasons as `numpy.get_include`,
see https://github.com/numpy/numpy/issues/14960#issuecomment-846460159

2 files changed, 62 insertions, 7 deletions

diff --git a/numpy/f2py/__init__.py b/numpy/f2py/__init__.py
index 07ab6cd7d..4f6938ed2 100644
--- a/numpy/f2py/__init__.py
+++ b/numpy/f2py/__init__.py
@@ -2,7 +2,7 @@
 """Fortran to Python Interface Generator.
 
 """
-__all__ = ['run_main', 'compile', 'f2py_testing']
+__all__ = ['run_main', 'compile', 'get_include', 'f2py_testing']
 
 import sys
 import subprocess
@@ -122,6 +122,53 @@ def compile(source,
         return cp.returncode
 
 
+def get_include():
+    """
+    Return the directory that contains the fortranobject.c and .h files.
+
+    .. note::
+
+        This function is not needed when building an extension with
+        `numpy.distutils` directly from ``.f`` and/or ``.pyf`` files
+        in one go.
+
+    Python extension modules built with f2py-generated code need to use
+    ``fortranobject.c`` as a source file, and include the ``fortranobject.h``
+    header. This function can be used to obtain the directory containing
+    both of these files.
+
+    Returns
+    -------
+    include_path : str
+        Absolute path to the directory containing ``fortranobject.c`` and
+        ``fortranobject.h``.
+
+    Notes
+    -----
+    .. versionadded:: 1.22.0
+
+    Unless the build system you are using has specific support for f2py,
+    building a Python extension using a ``.pyf`` signature file is a two-step
+    process. For a module ``mymod``:
+
+        - Step 1: run ``python -m numpy.f2py mymod.pyf --quiet``. This
+          generates ``_mymodmodule.c`` and (if needed)
+          ``_fblas-f2pywrappers.f`` files next to ``mymod.pyf``.
+        - Step 2: build your Python extension module. This requires the
+          following source files:
+
+              - ``_mymodmodule.c``
+              - ``_mymod-f2pywrappers.f`` (if it was generated in step 1)
+              - ``fortranobject.c``
+
+    See Also
+    --------
+    numpy.get_include : function that returns the numpy include directory
+
+    """
+    return os.path.join(os.path.dirname(__file__), 'src')
+
+
 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/
diff --git a/numpy/f2py/tests/test_regression.py b/numpy/f2py/tests/test_regression.py
index a1b772069..b91499e4a 100644
--- a/numpy/f2py/tests/test_regression.py
+++ b/numpy/f2py/tests/test_regression.py
@@ -25,23 +25,31 @@ class TestIntentInOut(util.F2PyTest):
         x = np.arange(3, dtype=np.float32)
         self.module.foo(x)
         assert_equal(x, [3, 1, 2])
- 
+
 
 class TestNumpyVersionAttribute(util.F2PyTest):
     # Check that th attribute __f2py_numpy_version__ is present
     # in the compiled module and that has the value np.__version__.
     sources = [_path('src', 'regression', 'inout.f90')]
-    
+
     @pytest.mark.slow
     def test_numpy_version_attribute(self):
-        
+
         # Check that self.module has an attribute named "__f2py_numpy_version__"
-        assert_(hasattr(self.module, "__f2py_numpy_version__"), 
+        assert_(hasattr(self.module, "__f2py_numpy_version__"),
                 msg="Fortran module does not have __f2py_numpy_version__")
-        
+
         # Check that the attribute __f2py_numpy_version__ is a string
         assert_(isinstance(self.module.__f2py_numpy_version__, str),
                 msg="__f2py_numpy_version__ is not a string")
-        
+
         # Check that __f2py_numpy_version__ has the value numpy.__version__
         assert_string_equal(np.__version__, self.module.__f2py_numpy_version__)
+
+
+def test_include_path():
+    incdir = np.f2py.get_include()
+    fnames_in_dir = os.listdir(incdir)
+    for fname in ('fortranobject.c', 'fortranobject.h'):
+        assert fname in fnames_in_dir
+