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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 calf(self, spec):
 """ Typical safe usage is this, which sets everything that could be problematic up. Requires the filename which everything will be produced to. """


        if not isinstance(spec, Spec):
            raise TypeError('spec must be of type Spec')

        if not spec.get(BUILD_DIR):
            tempdir = realpath(mkdtemp())
            spec.advise(CLEANUP, shutil.rmtree, tempdir)
            build_dir = join(tempdir, 'build')
            mkdir(build_dir)
            spec[BUILD_DIR] = build_dir
        else:
            build_dir = self.realpath(spec, BUILD_DIR)
            if not isdir(build_dir):
                logger.error("build_dir '%s' is not a directory", build_dir)
                raise_os_error(errno.ENOTDIR, build_dir)

        self.realpath(spec, EXPORT_TARGET)

        # Finally, handle setup which may set up the deferred advices,
        # as all the toolchain (and its runtime and/or its parent
        # runtime and related toolchains) spec advises should have been
        # done.
        spec.handle(SETUP)

        try:
            process = ('prepare', 'compile', 'assemble', 'link', 'finalize')
            for p in process:
                spec.handle('before_' + p)
                getattr(self, p)(spec)
                spec.handle('after_' + p)
            spec.handle(SUCCESS)
        except ToolchainCancel:
            # quietly handle the issue and move on out of here.
            pass
        finally:
            spec.handle(CLEANUP)