F2PY test suite#

F2PY’s test suite is present in the directory numpy/f2py/tests. Its aim is to ensure that Fortran language features are correctly translated to Python. For example, the user can specify starting and ending indices of arrays in Fortran. This behaviour is translated to the generated CPython library where the arrays strictly start from 0 index.

The directory of the test suite looks like the following:

./tests/
├── __init__.py
├── src
│   ├── abstract_interface
│   ├── array_from_pyobj
│   ├── // ... several test folders
│   └── string
├── test_abstract_interface.py
├── test_array_from_pyobj.py
├── // ... several test files
├── test_symbolic.py
└── util.py

Files starting with test_ contain tests for various aspects of f2py from parsing Fortran files to checking modules’ documentation. src directory contains the Fortran source files upon which we do the testing. util.py contains utility functions for building and importing Fortran modules during test time using a temporary location.

Adding a test#

F2PY’s current test suite predates pytest and therefore does not use fixtures. Instead, the test files contain test classes that inherit from F2PyTest class present in util.py.

class F2PyTest:
    code = None
    sources = None
    options = []
    skip = []
    only = []
    suffix = ".f"
    module = None
    module_name = None

This class many helper functions for parsing and compiling test source files. Its child classes can override its sources data member to provide their own source files. This superclass will then compile the added source files upon object creation andtheir functions will be appended to self.module data member. Thus, the child classes will be able to access the fortran functions specified in source file by calling self.module.[fortran_function_name].

Example#

Consider the following subroutines, contained in a file named add-test.f

        subroutine addb(k)
          real(8), intent(inout) :: k(:)
          k=k+1
        endsubroutine

        subroutine addc(w,k)
          real(8), intent(in) :: w(:)
          real(8), intent(out) :: k(size(w))
          k=w+1
        endsubroutine

The first routine addb simply takes an array and increases its elements by 1. The second subroutine addc assigns a new array k with elements greater that the elements of the input array w by 1.

A test can be implemented as follows:

class TestAdd(util.F2PyTest):
    sources = [util.getpath("add-test.f")]

    def test_module(self):
        k = np.array([1, 2, 3], dtype=np.float64)
        w = np.array([1, 2, 3], dtype=np.float64)
        self.module.subb(k)
        assert np.allclose(k, w + 1)
        self.module.subc([w, k])
        assert np.allclose(k, w + 1)

We override the sources data member to provide the source file. The source files are compiled and subroutines are attached to module data member when the class object is created. The test_module function calls the subroutines and tests their results.

Advanced F2PY use cases

F2PY and Windows