为什么从 MATLAB 调用此 python 脚本时无法正常工作？

Question

I am using a python script to control a stepper motor which drives a translation stage.
The stage has two limit switches, one near the motor, which sits on the bottom, and one away from the motor (top).
I reference the motor at the limit switch near the motor, which sets the internal stepcount of the controller to 0 at that location.

I however, want the default 0 position to always be at the top. So depending on which point I choose as reference, I have to recalculate the stepcount before sending it to the controller.

Like so:

 if self.__reference_point == 'near':
            steps = steps - 50000

When I call the function move_absolute(0) the motor then always moves to the top.

However, if I call this script from MATLAB with

lt = py.lt_control.LT('COM4');
lt.do_referencing();
lt.move_absolute(0);

the stage moves back to the bottom. So it seems the conversion of the stepcount fails somehow.
Why is that?
I have python 3.7.8 x64 installed.
The stepper controller is a nanotec SMCI33-1, if that is useful.

Here is most of the python file, i removed irrelevant functions.

import serial
import time
from decimal import Decimal
import signal

class MotorNotReferencedError(Exception):
    def __init__(self):
        super().__init__('Motor not referenced! Please call do_referencing()!')

class LT(object):
    
    def __init__(self, portname, reference='near', com_timeout=1):
        """
        Create a new motor control object.

        :param portname: The Port for the serial connection (e.g. 'COM4' for Windows, '/dev/ttyS1' for Linux)
        :param reference: Which limit switch will be used for referencing the motor, far means away from motor, near means near, coordinates are positive away from reference
        :param com_timeout: Timeout in sek for serial port
        """
        signal.signal(signal.SIGINT, self.sig_handler)
        signal.signal(signal.SIGTERM, self.sig_handler)
        self.__serial_port = serial.Serial(portname, 115200, timeout=com_timeout)
        self.__debug = False
        self.__substeps = 8 #does not do anything right now, for future
        self.__reference_point = reference
        self.__reference_changed = False
        self.__status = 1
        self.__positioning_error = 0
        self.setup_defaults()
        if not self.is_referenced():
            print('Referencing is required!')

    def __delete__(self, instance):
        if self.__serial_port:
            self.__serial_port.close()

    def __del__(self):
        if self.__serial_port:
            self.__serial_port.close()

    def sig_handler(self, sig, fr):
        self.stop()
        print('Keyboard Interrupt: Motor stopped!')

    def close(self):
        self.__serial_port.close()

    def query(self, message):
        """
        Send a message to the controller with newline char and reads response.

        :param message: The message to send, should be in proper syntax
        :returns: The response without newline
        :rtype: String
        """
        msg = message + '\r'
        if self.__debug: print(message)
        self.__serial_port.write(msg.encode())
        ans = self.__serial_port.read_until(b'\r').decode('utf-8')
        if len(ans) == 0:
            raise TimeoutError
        else:
            if self.__debug: print(ans.strip())
            return ans.strip()

    def is_referenced(self):
        """
        Check whether the motor is referenced.

        This is necessary after every loss of power to the controller
        :returns: True if motor is referenced
        :rtype: Boolean
        """
        ans = self.query('#1:is_referenced')
        if ans[-1] == '1' and not self.__reference_changed:
            return True
        else:
            return False

    def setup_defaults(self):
        self.command('#1g8') # microstepping, 8 microsteps per step
    
    def command(self, message):
        """
        Send commands to controller. Check if write was successful.

        This is simply a query wrapper that does a validity check on the commandsand checks the response of the controller. 

        :param message: Query like string, following the proper syntax
        :returns: True if operation was successful, else False
        :rtype: Boolean
        """
        ans = self.query(message)
        if ans[-1] == '?':
            return False
        else:
            return True

    def fetch_status(self):
        """
        Fetch status from controller, extract integer value, save positioning error and state to internal variable for later use.
        
        :returns: The status value
        :rtype: int
        .. seealso:: is_control_ready(), has_position_error()
        """
        #extract int value and mask only useful 4 bits
        tmp = self.query('#1$')[-3:]
        tmp = int(tmp)
        self.__status = tmp & 0xF
        #self.__status = int(self.query('#1$')[-3:]) & 0xF
        self.__positioning_error = (self.__status & 0b0100) >> 2
        return self.__status

    def is_control_ready(self):
        """
        Check if the control is ready for movement
        :returns: True if control is ready
        :rtype: Boolean
        """
        ans = self.fetch_status()
        if ans & 1:
            return True
        else:
            return False

    def has_positioning_error(self):
        """
        Check control if a positioning error has occured since last clear_positioning_error()
        :returns: True if a positioning error has occured
        :rtype: Boolean
        .. seealso:: clear_position_error
        """
        self.fetch_status()
        if self.__positioning_error:
            return True
        else:
            return False

    def clear_positioning_error(self, reset_position=False):
        """
        Clear the positioning error to reenable movement.

        :param reset_postiton: False (default): Absolute position does not change, True: Set current absolute position to 0
        """
        self.__positioning_error = 0
        if reset_position:
            self.query('#1D0')#1C')
            ans = ans[2:] # extract position
            self.query('#1D' + ans) # clear error and set position

    def steps_to_mm(self, steps):
        """
        Converts the number of steps to distance in millimeters

        :param steps: The number of steps
        :returns: The distance in millimeters
        """
        steps_per_turn = self.__substeps * 200
        return (1.25/steps_per_turn) * steps

    def mm_to_steps(self, mm):
        """
        Converts the distance in millimeters to number of steps

        :param mm: The distance in millimeters
        :returns: The number of steps
        """
        steps_per_turn = self.__substeps * 200
        return int(round(Decimal((steps_per_turn/1.25) * mm)))

    def wait_movement(self):
        """
        Wait for movement ot finish.
        """
        while not self.is_control_ready():
                time.sleep(0.1)       
        if self.has_positioning_error():
            # in endschalter gelaufen
            # reset position
            self.clear_positioning_error()
            print('Movement ended prematurely, limit switch engaged!')

    def stop(self):
        """
        Immediately stops the motor
        """
        self.command('#1S')

    def set_reference_point(self, reference):
        """
        Redefine the reference point.

        :param reference: Which limit switch will be used for referencing the motor, 'far' means away from motor, 'near' means near, coordinates are positive away from reference
        """
        self.__reference_point = reference
        self.__reference_changed = True
        print('Please reference motor again!')

    def do_referencing(self):
        """
        Reference the motor to the limit switch defined by the reference
        point.
        """
        self.command('#1p4')
        self.command('#1l5154') # endschalterverhalten auf r�ckw�rts vom schalter runterfahren
        if self.__reference_point == 'near':
            self.command('#1d1')
        else:
            self.command('#1d0')
        self.command('#1o4000')
        self.command('#1A')
        self.wait_movement()
        self.__reference_changed = False
        
    def move_relative(self, steps, speed=4000):
        """Move the Stage relative to its current position.

        :param steps: number of steps to travel, max 50000
        steps < 0: Movement towards reference
        steps > 0: Movemento away from reference
        :param speed: Speed in steps/s (max 16000)
        """
        if abs(steps) > 50000:
            print("Relative Movement: Too many steps!")
            return
        if self.__reference_point == 'far':
            self.command('#1d1')
        else:
            self.command('#1d0')
        self.command('#1o' + str(speed))
        self.command('#1s' + str(steps))
        self.command('#1A')
        self.wait_movement()

    def move_absolute(self, steps, speed=4000):
        """Move the Stage to absolute position, 0 is opposite of motor.

        :param steps: Absolute position between 0 and 50000
        :param speed: Speed in steps/s
        """
        if not self.is_referenced():
            raise MotorNotReferencedError
        if abs(steps) > 50000:
            print('Absolute Movement: Too many steps!')
            return
        print("" + str(steps))
        if not self.__reference_point == 'far':
            steps = steps - 50000
        print("" + str(steps))
        self.command('#1p2')
        self.command('#1o' + str(speed))
        self.command('#1s' + str(steps))
        self.command('#1A')
        self.wait_movement()

    def move_relative_mm(self, distance_mm, speed=3):
        """Move the Stage relative to its current position.

        :param distance_mm: travel distance in millimeters
         < 0: Movement away from motor
         > 0: Movement towards motor
        :param speed: Speed in mm/s
        """
        steps = self.mm_to_steps(distance_mm)
        speed = self.mm_to_steps(speed)
        self.move_relative(steps, speed)

    def move_absolute_mm(self, position_mm, speed=3):
        """Move the Stage to absolute position, 0 ist limit switch opposite of motor.

        :param position_mm: Absolute position between 0 and 39
        :param speed: Speed in mm/s
        """
        if not self.is_referenced():
            raise MotorNotReferencedError
        steps = self.mm_to_steps(position_mm)
        speed = self.mm_to_steps(speed)
        self.move_absolute(steps, speed)

    def get_position(self):
        """Return absolute position in steps.

        :returns: absolute position in steps
        """
        real_pos = int(self.query('#1C')[2:])
        if self.__reference_point == 'far':
            disp_pos = real_pos
        else:
            disp_pos = real_pos + 50000
        return disp_pos

Answer 1

So it seems, that str(steps) returns the floating point representation '0.0' when called from MATLAB, where it needs to be an integer '0' to work.

Changing it to str(int(steps)) fixed the problem.
But its strange that the normal python interpreter didn't have a problem with that.

As Cris Luengo pointed out: when calling lt.move_absolute(0) from MATLAB, the 0 is a floating point number. This is the difference to calling the same expression from a python command line.