Python返回无效语法E

Question

我正在用raspberry-pi编写一个简单的python程序，对python编程还很陌生。我定义了一个名为GetMessage的函数，它没有参数，返回一个我称之为data的变量，但是我得到了一个错误

File "Raspberry_pi.py", line 39

return none

    ^

SyntaxError: invalid syntax

import os
import glob
import time
import RPi.GPIO as GPIO
from math import *
from bluetooth import *
from RPIO import PWM

os.system('sudo hciconfig hci0 pisca')
os.system('sudo hciconfig hci0 name "De Quadcoptur"')
servo = PWM.Servo()
StartSpin()

server_sock=BluetoothSocket( RFCOMM )
server_sock.bind(("",PORT_ANY))
server_sock.listen(1)

port = server_sock.getsockname()[1]

GetMessage()
DecodeInput()

uuid = "94f39d29-7d6d-437d-973b-fba39e49d4ee"
def GetMessage():
    advertise_service( server_sock, "XT1032", #phone bluetooth name
        service_id = uuid,
        service_classes = [ uuid, SERIAL_PORT_CLASS ],
        profiles = [ SERIAL_PORT_PROFILE ],
        #protocols = [ OBEX_UUID ]
        )
    client_sock, client_info = server_sock.accept()

    try:
            data = client_sock.recv(1024)
            if len(data) == 0: break
            print "received [%s]" % data
            client_sock.close()
            server_sock.close()
    except IOError:
        pass

        break
    return data


def StartSpin():
    # Set servo on GPIO17 to 1200µs (1.2ms)
    servo.set_servo(17, 1000)
    servo.set_servo(18, 1000)
    servo.set_servo(19, 1000)
    servo.set_servo(20, 1000)
    time.sleep(1)
    servo.stop_servo(17)
    servo.stop_servo(18)
    servo.stop_servo(19)
    servo.stop_servo(20)
    #Check if more pulses is faster
    time.sleep(2000)
    PWM.add_channel_pulse(0, 17, start = 1000, width = 100)
    PWM.add_channel_pulse(0, 17, start = 1000, width = 100)
    PWM.add_channel_pulse(0, 17, start = 1000, width = 100)
    PWM.add_channel_pulse(0, 17, start = 1000, width = 100)
    PWM.add_channel_pulse(0, 17, start = 1000, width = 100)
    servo.stop_servo(17)
    servo.stop_servo(18)
    servo.stop_servo(19)
    servo.stop_servo(20)
    return None

def DecodeInput():
    data = GetMessage()
    if(data == 'start')
        StartSpin()
        return 0
    else if(data[0] == 'U')
        data.strip('U')
        UpPower = int(data)
        SetUpPower(UpPower)
    else if(data[0] == 'P')
        data.strip('P')
        PitchPower = int(data)
        SetPitchPower
    else
        data.strip('P')
        RollPower = int(data)
    SetPower(UpPower, PitchPower, RollPower)
    return None

def SetPower(UpPower, PitchPower, RollPower):
    #Make Arbitrary Values
    Motor1Power = UpPower #Front Left
    Motor2Power = UpPower #Front Right
    Motor3Power = UpPower #Back  Left
    Motor4Power = UpPower #Back  Right
    PitchPower = PitchPower /2
    RollPower = RollPower /2
    if(PitchPower < 25)
        Motor1Power = Motor1Power + abs(25-PitchPower)
        Motor2Power = Motor1Power + abs(25-PitchPower)
    else
        Motor3Power = Motor3Power + (PitchPower-25)
        Motor4Power = Motor4Power + (PitchPower-25)
    if(RollPower < 25)
        Motor1Power = Motor1Power + abs(25-RollPower)
        Motor3Power = Motor3Power + abs(25-RollPower)
    else
        Motor2Power = Motor2Power + (RollPower - 25)
        Motor4Power = Motor4Power + (RollPower - 25)

是什么导致了这个错误？我该如何修复它？

编辑：我已经将数据定义为全局变量，现在的错误是

File "Raspberry_pi.py", line 39

return data

    ^

SyntaxError: invalid syntax

Answer 1

一旦修复冒号，您可能会遇到GetMessage语法的问题。除非在循环中，否则不能break。如果要从异常返回，则不需要pass调用。一个例子（从您的代码中简化）说明了这个方法如何能够（应该？）看：

def GetMessage():
    data = None

    try:
        data = [1,2]
        if len(data) == 0: 
            return None
    except IOError:
        return None

    return data

很明显，您需要用自己的代码替换方法的大部分，并确定是否真的要从放breaks的位置的函数中return

Answer 2

代码中有许多语法问题。由于SyntaxError异常（在解释器不理解代码语法时引发）的性质，错误消息可能无法将正确的行标识为问题的根源。

我看到的第一个语法错误是您在GetMessage函数中使用break，而它没有在循环中。break语句只在for或while块中有用，而在其他地方（在本例中是在except块中）使用它是语法错误。

下一组错误与缺少冒号有关。DecodeInput和SetPower中的每个条件分支在条件之后都需要有一个冒号：if condition1:、elif condition2:、else:

使用else if而不是elif也是一个错误（如果在else:之后添加冒号、换行符和额外的缩进级别，然后使用单独的if语句，则可以使其正常工作，但这会浪费空间）。

还有一些额外的问题，但它们不是语法错误。例如，在定义函数之前，您是从顶层代码调用它们的，而DecodeInput有一个与裸表达式SetPower对应的行，它没有任何有用的功能（您可能想用一些参数调用SetPower）。

希望这能让你走上正轨。