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<chapter>
    <title>Script Component Usage</title>
    <sect1>
        <title>Synopsis</title>
        <para>The Script component allows the execution of a self-written script. Currently, two
            script languages are supported:<itemizedlist>
                <listitem>
                    <para>Python: must be installed on the executing system</para>
                </listitem>
                <listitem>
                    <para><ulink url="http://www.jython.org/">Jython</ulink>: a Java implementation
                        of Python.</para>
                </listitem>
            </itemizedlist></para>
    </sect1>
    <sect1>
        <title>Rationale</title>
        <para>Based on the selection, the component uses a natively installed Python version or the
            Java implementation Jython. This approach was selected on purpose because many users use
            their own specific modules and want to use Python for this, others are satisfied with
            the standard Python operations and need a faster implementation which is Jython.</para>
        <para>Limitations:</para>
        <para>Only single file scripts are allowed, because the user's script contents are converted
            into a temporary "wrapped" script, executed in the executor’s temporary directory. It's
            currently not possible to copy satellite files like modules or input data files to the
            directory, where the script is residing.</para>
        <para>The execution speed of the Python implementation is limited by the initial start-up
            time of the Python interpreter (or virtual machine, just-in-time compiler). Each script
            execution first wraps the user script into a temporary script file, then starts the
            Python executable in a new process and after that, processes the output bindings.</para>
        <para>Advantages of native Python: <itemizedlist>
                <listitem>
                    <para>100% binary compatibility </para>
                </listitem>
                <listitem>
                    <para>Exotic setups are supported automatically, including third-party modules,
                        binary libraries, <code>cpython</code> and so on. Users gain the benefit of
                        using additionally installed Python modules like
                            <code>&lt;&lt;numpy>></code>, <code>&lt;&lt;scipy>></code> or
                            <code>&lt;&lt;mysqldb>></code></para>
                </listitem>
                <listitem>
                    <para>Self-compiled Python interpreters with binary extensions can be
                        used</para>
                </listitem>
                <listitem>
                    <para>- No problems with library indexing as e.g. in Jython</para>
                </listitem>
            </itemizedlist></para>
    </sect1>
    <sect1>
        <title>Usage</title>
            <sect2>
                <title>Script API</title>
                <para>For interacting with RCE in the script execution, there is an API. All methods
                of this API are listed <link linkend="scriptApiReference">here</link>.</para>
                    <para><emphasis role="bold">How to use the script API:</emphasis></para>
                <para>Define your inputs and outputs in the Inputs/Outputs tab of the Properties
                view (appearing for the selected Script component on double click). Write your
                script in the Script tab (in the same Properties view). You can either do it in the
                text box or in a separate text editor by clicking on the button “Open in Editor”.
                For interacting with RCE from a script, there is a module called "RCE". To get an
                overview of all RCE API methods, look at<link linkend="scriptApiReference"> the
                    script API detailed description</link> The most important methods there are
                reading inputs and writing outputs. For reading an input, call the
                method<programlisting>RCE.read_input(String input_name)</programlisting>or<programlisting>RCE.read_input(String input_name, default value)</programlisting>You
                can write outputs within your script
                with<programlisting>RCE.write_output(String output_name, OutputDataType value)</programlisting>Thereby,
                the type (OutputDataType) of the value must fit the data type of the output (as
                defined in the tab Inputs/Outputs). File and Directory are represented by the
                absolute file paths.<note>
                    <para>The module RCE uses is already imported in the script during
                        execution.</para>
                </note></para>
            <para>Examples:</para>
            <para>If you like to double an incoming value (x is an input of type Integer and y an
                output of type
                Integer):<programlisting>RCE.write_output("y", RCE.read_input(2 * x))</programlisting>If
                you like to access an incoming file (f_in is an input of type
                File):<programlisting>file = open(RCE.read_input("f_in"),"r")</programlisting>If you
                like to send a file to an output (f_out is an output of type
                File):<programlisting>absolute_file_path = /home/user_1/my_file.txt
RCE.write_output("f_out", absolute_file_path)</programlisting>
                If an output is not needed any more (e.g. you want to end an inner loop), you can
                close an output using the
                command:<programlisting>RCE.close_output(String output_name)</programlisting>Example:<programlisting>RCE.close_output(“y”)</programlisting>The
                following components will get the finished signal.</para>
            <para>If a script fails because of some invalid parameters sent by a Parametric Study or
                Optimizer component, you can send a "not a value" signal to your output(s). It
                indicates, that the script failed because of invalid parameters and did not fail at
                all. This signal is ignored by most of the components, only the Parametric Study and
                the Optimizer component handle this signal. For sending it, use
                <programlisting>RCE.write_not_a_value_output(String outputname)</programlisting>For
                the other API methods refer to the example workflow "Script_with_all_API_methods.wf"
                from the workflow examples project.</para>
            </sect2>
        <sect2>
            <title>Script component states</title>
            <para>The Script component can keep its state from one run to another. Use the API to
                write and read state variables. The values are stored in a Python dictionary. They
                must be compatible with the RCE data types. Script components of nested loops are
                resetted if the nested loop has been terminated. Resetting a script component in a
                nested loop also resets its state map.</para>
        </sect2>
        <sect2>
            <title>Python Executable</title>
            <para>If Python was chosen as script language, the path to the Python executable must be
                chosen before as workflow start (in the second page of the workflow execution
                dialog). It must be done for every Script component of the workflow. If they all
                should use the same Python interpreter, the “Apply to all” button helps.</para>
        </sect2>
    </sect1>
    <sect1>
        <title><anchor id="scriptApiReference"/>Script API Reference</title>
        <informaltable frame="none">
            <tgroup cols="2">
                <colspec colname="c1" colnum="1" colwidth="1.0*"/>
                <colspec colname="c2" colnum="2" colwidth="1.0*"/>
                <thead>
                    <row>
                        <entry>Method</entry>
                        <entry>Description</entry>
                    </row>
                </thead>
                <tbody>
                    <row>
                            <entry><code>def RCE.close_all_outputs ( )</code>
                        </entry>
                        <entry>Closes all outputs that are known in RCE.</entry>
                    </row>
                    <row>
                            <entry><code>def RCE.close_output ( name )</code>
                        </entry>
                        <entry>Closes the RCE output with the given name</entry>
                    </row>
                    <row>
                            <entry><code>def RCE.fail ( reason )</code></entry>
                        <entry>Fails the RCE component with the given reason</entry>
                    </row>
                    <row>
                            <entry><code>def RCE.get_execution_count ( )</code>
                        </entry>
                        <entry>Returns the current execution count of the RCE component</entry>
                    </row>
                    <row>
                            <entry><code>def RCE.get_input_names_with_datum ( )</code>
                        </entry>
                        <entry>Returns all input names that have got a data value from RCE.</entry>
                    </row>
                    <row>
                            <entry><code>def RCE.get_output_names ( )</code></entry>
                        <entry>Returns the read names of all outputs from RCE</entry>
                    </row>
                    <row>
                            <entry><code>def RCE.get_state_dict ( ) </code></entry>
                        <entry>Returns the current state dictionary</entry>
                    </row>
                    <row>
                        <entry><code>def RCE.getallinputs ( )</code></entry>
                        <entry>Gets a dictionary with all inputs from RCE</entry>
                    </row>
                    <row>
                        <entry><code>def RCE.read_input ( name ) </code></entry>
                        <entry>Gets the value for the given input name or an error, if the input is
                            not there (e.g. not required and it got no value)</entry>
                    </row>
                    <row>
                        <entry><code>def RCE.read_input ( name , defaultvalue ) </code></entry>
                        <entry>Gets the value for the given input name or returns the default value
                            if there is no input connected and the input not required</entry>
                    </row>
                    <row>
                        <entry><code>def RCE.read_state_variable ( name ) </code></entry>
                        <entry>Reads the given state variables value, if it exists, else None is
                            returned</entry>
                    </row>
                    <row>
                        <entry><code>def RCE.read_state_variable ( name, defaultvalue
                            )</code></entry>
                        <entry>Reads the given state variables value, if it exists, else a the
                            default value is returned and stored in the dictionary</entry>
                    </row>
                    <row>
                        <entry><code>def RCE.write_not_a_value_output ( name ) </code></entry>
                        <entry>Sets the given output to "not a value" data type</entry>
                    </row>
                    <row>
                        <entry><code>def RCE.write_output ( name, value )</code></entry>
                        <entry>Sets the given value to the output "name" which will be read from
                            RCE</entry>
                    </row>
                    <row>
                        <entry><code>def RCE.write_state_variable ( name, value )</code></entry>
                        <entry>Writes a variable name in the dictionary for the components
                            state</entry>
                    </row>
                </tbody>
            </tgroup>
        </informaltable>
    </sect1>
</chapter>
