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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 _write_expressiontool(step_dir, name, inputs, outputs, expression, parallel):
 """Create an ExpressionTool output for the given inputs """

    out_file = os.path.join(step_dir, "%s.cwl" % name)
    out = {"class": "ExpressionTool",
           "cwlVersion": "v1.0",
           "requirements": [{"class": "InlineJavascriptRequirement"}],
           "inputs": [],
           "outputs": [],
           "expression": expression}
    out = _add_inputs_to_tool(inputs, out, parallel)
    out = _add_outputs_to_tool(outputs, out)
    _tool_to_file(out, out_file)
    return os.path.join("steps", os.path.basename(out_file))