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## title = Writing a Simple Action Client (Python)
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## description = This tutorial covers using the action_client library to create a Fibonacci simple action client in Python.
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<<IncludeCSTemplate(TutorialCSHeaderTemplate)>>

<<TableOfContents(4)>>

The code and examples used in this tutorial can be found in the [[actionlib_tutorials]] package.  You may want to read about the [[actionlib]] package before starting this tutorial.

== The Code ==

The following code can be found in [[https://github.com/ros/common_tutorials/blob/hydro-devel/actionlib_tutorials/scripts/fibonacci_client.py|actionlib_tutorials repository]], and implements a simple python action client for the [[http://docs.ros.org/api/actionlib_tutorials/html/classfibonacci__server_1_1FibonacciAction.html|fibonacci action]].

{{{
#!python block=action
#! /usr/bin/env python

import rospy
from __future__ import print_function

# Brings in the SimpleActionClient
import actionlib

# Brings in the messages used by the fibonacci action, including the
# goal message and the result message.
import actionlib_tutorials.msg

def fibonacci_client():
    # Creates the SimpleActionClient, passing the type of the action
    # (FibonacciAction) to the constructor.
    client = actionlib.SimpleActionClient('fibonacci', actionlib_tutorials.msg.FibonacciAction)

    # Waits until the action server has started up and started
    # listening for goals.
    client.wait_for_server()

    # Creates a goal to send to the action server.
    goal = actionlib_tutorials.msg.FibonacciGoal(order=20)

    # Sends the goal to the action server.
    client.send_goal(goal)

    # Waits for the server to finish performing the action.
    client.wait_for_result()

    # Prints out the result of executing the action
    return client.get_result()  # A FibonacciResult

if __name__ == '__main__':
    try:
        # Initializes a rospy node so that the SimpleActionClient can
        # publish and subscribe over ROS.
        rospy.init_node('fibonacci_client_py')
        result = fibonacci_client()
        print("Result:", ', '.join([str(n) for n in result.sequence]))
    except rospy.ROSInterruptException:
        print("program interrupted before completion", file=sys.stderr)
}}}

== The Code, explained ==

<<CodeRef(action,11,11)>>

The action specification generates several messages for sending goals, receiving feedback, etc...  This line imports the generated messages.

<<CodeRef(action,16,16)>>

The action client and server communicate over a set of topics, described in [[actionlib/DetailedDescription|the actionlib protocol]].  The action name describes the namespace containing these topics, and the action specification message describes what messages should be passed along these topics.

<<CodeRef(action,20,20)>>

Sending goals before the action server comes up would be useless.  This line waits until we are connected to the action server.

<<CodeRef(action,22,26)>>

Creates a goal and sends it to the action server.

<<CodeRef(action,28,32)>>

The action server will process the goal and eventually terminate.  We want the result from the termination, but we wait until the server has finished with the goal.

== Running the Client ==

Before running the client, we assume `roscore` ans Action server are already running from [[actionlib_tutorials/Tutorials/Writing a Simple Action Server using the Execute Callback (Python)#Compiling|previous page]].

Start the client.  It will start up, send a goal to the server, wait for the goal to complete, and then exit.

{{{
$ rosrun actionlib_tutorials fibonacci_client.py
}}}

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