build the scripts and return a string

def build(self):
        """build the scripts and return a string"""

        if not self.embed:
            mkdir_recursive(self.output_directory)

        # get list of script files in build order
        self.build_order = remove_dups(
            reduce(lambda a, b: a + glob.glob(b),
                   self.build_targets,
                   []))
        self.build_order_output = [self.out_path_of(t)
                                   for (t) in self.build_order]
        self.path_mapping = dict(zip(
            self.build_order,
            self.build_order_output))

        self.compiled_scripts = {}
        exceptions, values = partition(
            lambda x: isinstance(x, Exception),
            [self.compile_and_process(target)
             for target in self.build_order])

        self.compiled_scripts.update(dict(values))

        saneExceptions, insaneExceptions = partition(
            lambda x: isinstance(x, TaskExecutionException),
            exceptions)

        if len(insaneExceptions) != 0:
            raise insaneExceptions[0]

        if len(exceptions) != 0:
            raise TaskExecutionException(
                "Precompiler Errors (%s):" % type(self).__name__,
                "\n".join([
                    x.header + "\n    " +
                    x.message.replace("\n", "\n    ")
                    for x in exceptions]))

        return self.collect_output()