Question

我是python和ros的新手，我现在有一个小问题。我确信这对我来说是一个简单的错误，但我无法弄明白。

我搜索并发现了类似的情况，但我不确定如何实现我的代码中其他答案的解决方案。

请忽略我的代码中没有直接导致问题的任何“困惑”。我只需要这个项目尽快运行。

#!/usr/bin/env python

import rospy
from geometry_msgs.msg import Twist, Vector3Stamped
from math import radians
from sensor_msgs.msg import NavSatFix
import geometry_msgs.msg
import time
import numpy

global distance
global pub
global dest_lat
global dest_long
global move_cmd
global turn_cmd
global bearing
global heading
global initial_bearing
global cur_lat
global prev_lat
global cur_long
global prev_long

bearing = 0

################################################################################
lat_dest = 30.210406
#                                                   DESTINATION COORDINATES
long_dest = -92.022914
################################################################################

move_cmd = Twist()
turn_cmd = Twist()

def nav_dist(navsat):
    R = 6373000        # Radius of the earth in m
    cur_lat = navsat.latitude
    cur_long = navsat.longitude
    dLat = cur_lat - lat_dest
    dLon = cur_long - long_dest
    x = dLon * numpy.cos((lat_dest+cur_lat)/2)
    distance = numpy.sqrt(x**2 + dLat**2) * R
    return distance


def bearing():
    if (bearing == 0):
        bearing = initial_bearing
        return bearing
    else:
        bearing = calculate_bearing(cur_lat, prev_lat, cur_long, prev_long)
        return bearing


def calculate_bearing(lat1, lat2, long1, long2):
    dLon = long2 - long1
    y = np.sin(dLon) * np.cos(lat2)
    x = np.cos(lat1)*np.sin(lat2) - np.sin(lat1)*np.cos(lat2)*np.cos(dLon)
    bearing = (np.rad2deg(np.arctan2(y, x)) + 360) % 360
    return bearing

def calculate_nav_angle(lat1, lat_dest, long1, long_dest):
    dLon = long_dest - long1
    y = np.sin(dLon) * np.cos(lat_dest)
    x = np.cos(lat1)*np.sin(lat_dest) - np.sin(lat1)*np.cos(lat_dest)*np.cos(dLon)
    heading = (np.rad2deg(np.arctan2(y, x)) + 360) % 360
    return heading

def navigate(distance, nav_angle):
    turn_cmd.angular.z = radians(bearing - heading)
    move_cmd.linear.x = distance
    pub.publish(turn_cmd)
    time.sleep(.01)
    pub.publish(move_cmd)
    time.sleep(.001)

    prev_long = cur_long
    prev_lat = cur_lat

###############################################################################################

#################################    callbacks and run    #################################

###############################################################################################

def call_nav(navsat):
    rospy.loginfo("Latitude: %s", navsat.latitude)      #Print GPS co-or to terminal
    rospy.loginfo("Longitude: %s", navsat.longitude)
    nav_dist(navsat)
    time.sleep(.001)


def call_bear(bearing):
    rospy.loginfo("Bearing: %s", bearing.vector)            #Print mag reading for bearing
    x = -bearing.vector.y
    y = bearing.vector.z
    initial_bearing = numpy.arctan2(y, x)
    return initial_bearing

def run():
    pub = rospy.Publisher('/husky_velocity_controller/cmd_vel', Twist)
    rospy.Subscriber("/imu_um6/mag", Vector3Stamped, call_bear)
    rospy.Subscriber("/gps/fix", NavSatFix, call_nav)
    rospy.init_node('navigate_that_husky')

    rospy.spin()

if __name__ == '__main__':
    run()
    navigate(distance, nav_angle)

这是错误

Traceback (most recent call last):
  File "NewTest.py", line 111, in <module>
    navigate(distance, nav_angle)
NameError: global name 'distance' is not defined

我该如何解决这个问题？我感谢任何帮助。

Answer 1

在您的函数中，您将全局变量distance重新定义为本地变量

Answer 2

在python中，global不会将变量标记为全局变量; global进入函数内部以允许函数修改变量。

例如：

def eggs():
    x = 5 #<- local variable
    print(x)

x = 10 #<- top-level variable
eggs() #<- prints 5
print(x) #<- prints 10 because the function doesn't touch the top-level variable

然而：

def eggs():
    global x
    x = 5 #<- modify the top level variable
    print(x)

x = 10 #<- top-level variable
eggs() #<- prints 5
print(x) #<- prints 5 because now the function can modify the top-level veriable

未定义全局名称“距离”

2 个答案: