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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def is_macos_gfortran(f90_compiler):
 """Checks if the current build is ``gfortran`` on macOS. Args: f90_compiler (numpy.distutils.fcompiler.FCompiler):
 A Fortran compiler instance. Returns: bool: Only :data:`True` if * Current OS is macOS (checked via ``sys.platform``). * ``f90_compiler`` corresponds to ``gfortran``. """

    # NOTE: NumPy may not be installed, but we don't want **this** module to
    #       cause an import failure.
    from numpy.distutils.fcompiler import gnu

    # Only macOS.
    if sys.platform != MAC_OS:
        return False

    # Only ``gfortran``.
    if not isinstance(f90_compiler, gnu.Gnu95FCompiler):
        return False

    return True