After learning the fourth lesson of Mr. Gu Yue’s ROS, I started the keyboard control of the robot and reported this error in the launch file. The following is the error content:
process[mbot_teleop-1]: started with pid [4942]
File "/home/zxf/catkin_ws/src/mbot_teleop/scripts/mbot_teleop.py", line 78
print msg
^
SyntaxError: Missing parentheses in call to 'print'. Did you mean print(msg)?
[mbot_teleop-1] process has died [pid 4942, exit code 1, cmd /home/zxf/catkin_ws/src/mbot_teleop/scripts/mbot_teleop.py __name:=mbot_teleop __log:=/home/zxf/.ros/log/4e9341ca-0155-11ec-8ec5-cf95496c0738/mbot_teleop-1.log].
log file: /home/zxf/.ros/log/4e9341ca-0155-11ec-8ec5-cf95496c0738/mbot_teleop-1*.log
I searched the Internet and found that it was because of the version of python2. X was incompatible with the version of python3. X. The reason for the error lies in the print output syntax. A simple example is hello ROS
python2.x
print "hello ROS"
Output: hello ROS
print 'hello ROS'
Output: hello ROS
print ('hello ROS')
Output: hello ROS
print ("hello ROS")
Output: hello ROS
The above four methods can be applied in Python 2. X, but not necessarily in Python 3. X
python3.x
print("hello ROS")
Output: hello ROS
print(hello ROS)
Output: hello ROS
I use Ubuntu 20.04, so it is the Python 3 version, which is different from that used by Gu Yue, so I need to modify ~/catkin_ws/src/mbot_teleop/scripts/mbot_ Teleop.py file
#!/usr/bin/env python
# -*- coding: utf-8 -*-
import rospy
from geometry_msgs.msg import Twist
import sys, select, termios, tty
msg = """
Control mbot!
---------------------------
Moving around:
u i o
j k l
m , .
q/z : increase/decrease max speeds by 10%
w/x : increase/decrease only linear speed by 10%
e/c : increase/decrease only angular speed by 10%
space key, k : force stop
anything else : stop smoothly
CTRL-C to quit
"""
moveBindings = {
'i':(1,0),
'o':(1,-1),
'j':(0,1),
'l':(0,-1),
'u':(1,1),
',':(-1,0),
'.':(-1,1),
'm':(-1,-1),
}
speedBindings={
'q':(1.1,1.1),
'z':(.9,.9),
'w':(1.1,1),
'x':(.9,1),
'e':(1,1.1),
'c':(1,.9),
}
def getKey():
tty.setraw(sys.stdin.fileno())
rlist, _, _ = select.select([sys.stdin], [], [], 0.1)
if rlist:
key = sys.stdin.read(1)
else:
key = ''
termios.tcsetattr(sys.stdin, termios.TCSADRAIN, settings)
return key
speed = .2
turn = 1
def vels(speed,turn):
return "currently:\tspeed %s\tturn %s " % (speed,turn)
if __name__=="__main__":
settings = termios.tcgetattr(sys.stdin)
rospy.init_node('mbot_teleop')
pub = rospy.Publisher('/cmd_vel', Twist, queue_size=5)
x = 0
th = 0
status = 0
count = 0
acc = 0.1
target_speed = 0
target_turn = 0
control_speed = 0
control_turn = 0
try:
print(msg)
print(vels(speed,turn))
while(1):
key = getKey()
if key in moveBindings.keys():
x = moveBindings[key][0]
th = moveBindings[key][1]
count = 0
elif key in speedBindings.keys():
speed = speed * speedBindings[key][0]
turn = turn * speedBindings[key][1]
count = 0
print(vels(speed,turn))
if (status == 14):
print(msg)
status = (status + 1) % 15
elif key == ' ' or key == 'k' :
x = 0
th = 0
control_speed = 0
control_turn = 0
else:
count = count + 1
if count > 4:
x = 0
th = 0
if (key == '\x03'):
break
target_speed = speed * x
target_turn = turn * th
if target_speed > control_speed:
control_speed = min( target_speed, control_speed + 0.02 )
elif target_speed < control_speed:
control_speed = max( target_speed, control_speed - 0.02 )
else:
control_speed = target_speed
if target_turn > control_turn:
control_turn = min( target_turn, control_turn + 0.1 )
elif target_turn < control_turn:
control_turn = max( target_turn, control_turn - 0.1 )
else:
control_turn = target_turn
twist = Twist()
twist.linear.x = control_speed;
twist.linear.y = 0;
twist.linear.z = 0
twist.angular.x = 0;
twist.angular.y = 0;
twist.angular.z = control_turn
pub.publish(twist)
except:
print(e)
finally:
twist = Twist()
twist.linear.x = 0; twist.linear.y = 0; twist.linear.z = 0
twist.angular.x = 0; twist.angular.y = 0; twist.angular.z = 0
pub.publish(twist)
termios.tcsetattr(sys.stdin, termios.TCSADRAIN, settings)
It is probably to add () to the print output statement on lines 78, 79, 93, 95 and 141.
