Roboclaw实例报AttributeError:无_port属性问题求助（Python2.7环境）

Let's tackle this issue step by step— I've dealt with similar Python 2.7/3 compatibility headaches with Roboclaw scripts before, so here's what's going on and how to fix it without breaking your Raspbian system.

First, that AttributeError is telling you the Roboclaw class instance doesn't have a _port attribute when it tries to write to the serial port. This usually happens from one of two things: either you're not initializing the Roboclaw object correctly, or the Python 2.7 script isn't playing nice with your environment (even if you're using Python 2.7).

Step 1: Make Sure You're Running the Script with Python 2.7 #

The official Roboclaw script is built for Python 2.7, so double-check you're invoking it with the right interpreter. On Raspbian Stretch, python might still point to Python 2.7, but it's safer to be explicit:

python2 roboclaw_simplepwm.py

If you accidentally run it with python3, you'll hit compatibility issues right away—even if you installed python3-serial.

Step 2: Verify Roboclaw Initialization in Your Script #

Take a look at how you're setting up the Roboclaw object. You need to properly initialize it with the correct serial port path (like /dev/ttyACM0 or /dev/ttyUSB0) and open the port before sending commands. Here's the correct pattern:

from roboclaw import Roboclaw

# Initialize with your serial port and baud rate (default is 38400)
rc = Roboclaw("/dev/ttyACM0", 38400)
# Critical: Open the port to create the _port attribute
rc.Open()

# Now send your command
address = 0x80  # Default Roboclaw address
rc.ForwardM1(address, 32)

If you skip rc.Open() or initialize the Roboclaw object incorrectly, the _port attribute won't be created, leading to that error.

Step 3: Check the Roboclaw Class's __init__ Method #

Open up the roboclaw.py file and look at the __init__ method. It should be creating the serial port instance and assigning it to self._port. If that line is missing or broken, add it:

import serial

class Roboclaw:
    def __init__(self, port, baudrate=38400, timeout=0.1):
        # This line is critical— it creates the _port attribute
        self._port = serial.Serial(port, baudrate, timeout=timeout)
        # Rest of the original __init__ code follows...

Some older versions of the Roboclaw script might have this setup in the Open() method instead, but if it's not properly assigning to self._port, you'll get the error.

Step 4: Fix Serial Port Permissions (Common Gotcha) #

Even if you have python-serial installed, your user might not have permission to access the serial port. Add yourself to the dialout group to fix this:

sudo usermod -a -G dialout $USER

You'll need to log out and log back in for this change to take effect.

Step 5: Optional: Make the Script Python 3 Compatible #

If you really want to use Python 3 instead of sticking with 2.7, you can modify the Roboclaw script to handle Python 3's bytes/string differences:

• Replace any chr(address) calls with bytes([address]) (since Python 3 serial writes require bytes, not strings)
• Update print statements to use parentheses (e.g., print("Command sent") instead of print "Command sent")
• Adjust any serial read operations to decode bytes to strings if needed

For example, modify the _sendcommand method in roboclaw.py:

def _sendcommand(self, address, cmd):
    self._port.write(bytes([address]))
    self._port.write(bytes([cmd]))

Don't Uninstall System Python! #

You were right to hold off on uninstalling Python versions—Raspbian/Debian relies heavily on Python for package management, so removing system Python will break your OS. Instead, use a virtual environment to isolate your Python 2.7 setup:

# Install virtualenv for Python 2.7
sudo apt-get install python-virtualenv
# Create a dedicated Python 2.7 environment
virtualenv -p python2.7 roboclaw_env
# Activate the environment
source roboclaw_env/bin/activate
# Install pyserial inside the environment
pip install pyserial
# Run your script here
python roboclaw_simplepwm.py
# Deactivate when finished
deactivate

This keeps your system Python untouched while giving you a clean environment for the Roboclaw script.

内容的提问来源于stack exchange，提问作者ecorrales