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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 export_select_fields_csv_action( description="Export selected objects as CSV file", fields=None, exclude=None, header=True):
 """ This function returns an export csv action 'fields' is a list of tuples denoting the field and label to be exported. Labels make up the header row of the exported file if header=True. fields=[ ('field1', 'label1'), ('field2', 'label2'), ('field3', 'label3'), ] 'exclude' is a flat list of fields to exclude. If 'exclude' is passed, 'fields' will not be used. Either use 'fields' or 'exclude.' exclude=['field1', 'field2', field3] 'header' is whether or not to output the column names as the first row From: http://djangosnippets.org/snippets/2712/ Which is in turn based on: http://djangosnippets.org/snippets/2020/ """

    def export_as_csv(modeladmin, request, queryset):
        """
        Generic csv export admin action.
        based on http://djangosnippets.org/snippets/1697/
        """
        opts = modeladmin.model._meta
        field_names = [field.name for field in opts.fields]
        labels = []
        if exclude:
            field_names = [v for v in field_names if v not in exclude]
        elif fields:
            field_names = [k for k, v in fields if k in field_names]
            labels = [v for k, v in fields if k in field_names]

        response = HttpResponse(mimetype='text/csv')
        response['Content-Disposition'] = ('attachment; filename=%s.csv'
                                           % unicode(opts).replace('.', '_'))

        writer = csv.writer(response)
        if header:
            if labels:
                writer.writerow(labels)
            else:
                writer.writerow(field_names)
        for obj in queryset:
            writer.writerow([unicode(getattr(obj, field)).encode('utf-8')
                            for field in field_names])
        return response
    export_as_csv.short_description = description
    return export_as_csv