Please help me to convert a function from vb to python

[Bokka]

Hello everyone! So far I have always programmed with visual basic, but I happened to have to convert my code into python. I would need if somebody can convert this function from vb to python (2.7):

Sub Modbus_CRC(strInput As String) As String 
    Dim RetCRC As String
    Dim RetStr As String
   
    Dim CRCREG As Int
    Dim MVAL As Int
   
    Dim R As Short
    Dim I As Short
    Dim A As Int
    Dim B As Int
   
    CRCREG = 0xFFFF

    For R = 0 To strInput.Length - 1 Step 2
        RetStr = strInput.SubString2(R, R + 2)
        MVAL = Bit.ParseInt(RetStr, 16)
       
        CRCREG = Bit.Xor(CRCREG, MVAL)
        CRCREG = Bit.And(CRCREG, 0xFFFF)

        For I = 1 To 8 Step 1
            If Bit.And(CRCREG, 0x01) = 1 Then
                CRCREG = Bit.Xor(Bit.UnsignedShiftRight(CRCREG, 1), 0xA001)
                CRCREG = Bit.And(CRCREG, 0xFFFF)
            Else
                CRCREG = Bit.UnsignedShiftRight(CRCREG, 1)
                CRCREG = Bit.And(CRCREG, 0xFFFF)
            End If
        Next
    Next

    A = Bit.And(CRCREG, 0xFF)
    B = Bit.And(CRCREG, 0xFF00)
    A = A * 256
    B = B / 256

    If (A + B) < 16 Then
        RetCRC = "000" & (A + B)
    Else If (A + B) < 256 Then
        RetCRC = "00" & Bit.ToHexString(A + B)
    Else If (A + B) < 4096 Then
        RetCRC = "0" & Bit.ToHexString(A + B)
    Else
        RetCRC = Bit.ToHexString(A + B)
    End If
   
    Return RetCRC.ToUpperCase
End Sub

If someone can do it, thanks in advance!!!

[micseydel]

You're probably going to have a hard time getting someone to do that for you. If you give it a try, we'd be enthusiastic to help you learn Python, though. You'll get the best result if you keep snippets (especially of non-Python) to 5-10 lines tops.

[Bokka]

You're probably going to have a hard time getting someone to do that for you. If you give it a try, we'd be enthusiastic to help you learn Python, though. You'll get the best result if you keep snippets (especially of non-Python) to 5-10 lines tops.

Thanks for the reply! But I can't find the button for edit my post now....

[micseydel]

There's no need to edit your post, just add a new one to this thread with your Python questions :)

[Bokka]

I have that code, but I get a generic "Syntax error", I can't understand where I wrong...

def calc(data):
        crc_table=[0x0000,0xC0C1,0xC181,0x0140,0xC301,0x03C0,0x0280,0xC241,0xC601,0x06C0,0x0780,0xC741,0x0500,0xC5C1,0xC481,0x0440,0xCC01,0x0CC0,0x0D80,0xCD41,0x0F00,0xCFC1,0xCE81,0x0E40,0x0A00,0xCAC1,0xCB81,0x0B40,0xC901,0x09C0,0x0880,0xC841,0xD801,0x18C0,0x1980,0xD941,0x1B00,0xDBC1,0xDA81,0x1A40,0x1E00,0xDEC1,0xDF81,0x1F40,0xDD01,0x1DC0,0x1C80,0xDC41,0x1400,0xD4C1,0xD581,0x1540,0xD701,0x17C0,0x1680,0xD641,0xD201,0x12C0,0x1380,0xD341,0x1100,0xD1C1,0xD081,0x1040,0xF001,0x30C0,0x3180,0xF141,0x3300,0xF3C1,0xF281,0x3240,0x3600,0xF6C1,0xF781,0x3740,0xF501,0x35C0,0x3480,0xF441,0x3C00,0xFCC1,0xFD81,0x3D40,0xFF01,0x3FC0,0x3E80,0xFE41,0xFA01,0x3AC0,0x3B80,0xFB41,0x3900,0xF9C1,0xF881,0x3840,0x2800,0xE8C1,0xE981,0x2940,0xEB01,0x2BC0,0x2A80,0xEA41,0xEE01,0x2EC0,0x2F80,0xEF41,0x2D00,0xEDC1,0xEC81,0x2C40,0xE401,0x24C0,0x2580,0xE541,0x2700,0xE7C1,0xE681,0x2640,0x2200,0xE2C1,0xE381,0x2340,0xE101,0x21C0,0x2080,0xE041,0xA001,0x60C0,0x6180,0xA141,0x6300,0xA3C1,0xA281,0x6240,0x6600,0xA6C1,0xA781,0x6740,0xA501,0x65C0,0x6480,0xA441,0x6C00,0xACC1,0xAD81,0x6D40,0xAF01,0x6FC0,0x6E80,0xAE41,0xAA01,0x6AC0,0x6B80,0xAB41,0x6900,0xA9C1,0xA881,0x6840,0x7800,0xB8C1,0xB981,0x7940,0xBB01,0x7BC0,0x7A80,0xBA41,0xBE01,0x7EC0,0x7F80,0xBF41,0x7D00,0xBDC1,0xBC81,0x7C40,0xB401,0x74C0,0x7580,0xB541,0x7700,0xB7C1,0xB681,0x7640,0x7200,0xB2C1,0xB381,0x7340,0xB101,0x71C0,0x7080,0xB041,0x5000,0x90C1,0x9181,0x5140,0x9301,0x53C0,0x5280,0x9241,0x9601,0x56C0,0x5780,0x9741,0x5500,0x95C1,0x9481,0x5440,0x9C01,0x5CC0,0x5D80,0x9D41,0x5F00,0x9FC1,0x9E81,0x5E40,0x5A00,0x9AC1,0x9B81,0x5B40,0x9901,0x59C0,0x5880,0x9841,0x8801,0x48C0,0x4980,0x8941,0x4B00,0x8BC1,0x8A81,0x4A40,0x4E00,0x8EC1,0x8F81,0x4F40,0x8D01,0x4DC0,0x4C80,0x8C41,0x4400,0x84C1,0x8581,0x4540,0x8701,0x47C0,0x4680,0x8641,0x8201,0x42C0,0x4380,0x8341,0x4100,0x81C1,0x8081,0x4040]
        

        crc_hi=0xFF
        crc_lo=0xFF

        for w in data:
                index=crc_lo ^ ord(w)
                crc_val=crc_table[index]
                crc_temp=crc_val/256
                crc_val_low=crc_val-(crc_temp*256)
                crc_lo=crc_val_low ^ crc_hi
                crc_hi=crc_temp

        crc=crc_hi*256 +crc_lo
        print (crc)
        return crc

[ichabod801]

I'm not getting a syntax error. I am getting a type error, but that may be because I don't understand what your data looks like.

Please rerun it with a small set of data. Then show use the data you used, and the complete error message you get.

[Bokka]

I'm not getting a syntax error. I am getting a type error, but that may be because I don't understand what your data looks like.

Please rerun it with a small set of data. Then show use the data you used, and the complete error message you get.

I need to create a function for calculate the CRC16 of a string.

For example, for the string:

11 01 00 03 00 0C

The CRC calculated must be

CE9F (CE High, 9F Low)

And for the string


11 01 02 CD 0B

The result of the CRC must be

6D 68

I'm trying to make some steps, but I am far away from the results....


This is what I do in python:

Python 2.7.13 (v2.7.13:a06454b1afa1, Dec 17 2016, 20:42:59) [MSC v.1500 32 bit (Intel)] on win32
Type "copyright", "credits" or "license()" for more information.
>>> def calc(data):
            crc_table=[0x0000,0xC0C1,0xC181,0x0140,0xC301,0x03C0,0x0280,0xC241,0xC601,0x06C0,0x0780,0xC741,0x0500,0xC5C1,0xC481,0x0440,0xCC01,0x0CC0,0x0D80,0xCD41,0x0F00,0xCFC1,0xCE81,0x0E40,0x0A00,0xCAC1,0xCB81,0x0B40,0xC901,0x09C0,0x0880,0xC841,0xD801,0x18C0,0x1980,0xD941,0x1B00,0xDBC1,0xDA81,0x1A40,0x1E00,0xDEC1,0xDF81,0x1F40,0xDD01,0x1DC0,0x1C80,0xDC41,0x1400,0xD4C1,0xD581,0x1540,0xD701,0x17C0,0x1680,0xD641,0xD201,0x12C0,0x1380,0xD341,0x1100,0xD1C1,0xD081,0x1040,0xF001,0x30C0,0x3180,0xF141,0x3300,0xF3C1,0xF281,0x3240,0x3600,0xF6C1,0xF781,0x3740,0xF501,0x35C0,0x3480,0xF441,0x3C00,0xFCC1,0xFD81,0x3D40,0xFF01,0x3FC0,0x3E80,0xFE41,0xFA01,0x3AC0,0x3B80,0xFB41,0x3900,0xF9C1,0xF881,0x3840,0x2800,0xE8C1,0xE981,0x2940,0xEB01,0x2BC0,0x2A80,0xEA41,0xEE01,0x2EC0,0x2F80,0xEF41,0x2D00,0xEDC1,0xEC81,0x2C40,0xE401,0x24C0,0x2580,0xE541,0x2700,0xE7C1,0xE681,0x2640,0x2200,0xE2C1,0xE381,0x2340,0xE101,0x21C0,0x2080,0xE041,0xA001,0x60C0,0x6180,0xA141,0x6300,0xA3C1,0xA281,0x6240,0x6600,0xA6C1,0xA781,0x6740,0xA501,0x65C0,0x6480,0xA441,0x6C00,0xACC1,0xAD81,0x6D40,0xAF01,0x6FC0,0x6E80,0xAE41,0xAA01,0x6AC0,0x6B80,0xAB41,0x6900,0xA9C1,0xA881,0x6840,0x7800,0xB8C1,0xB981,0x7940,0xBB01,0x7BC0,0x7A80,0xBA41,0xBE01,0x7EC0,0x7F80,0xBF41,0x7D00,0xBDC1,0xBC81,0x7C40,0xB401,0x74C0,0x7580,0xB541,0x7700,0xB7C1,0xB681,0x7640,0x7200,0xB2C1,0xB381,0x7340,0xB101,0x71C0,0x7080,0xB041,0x5000,0x90C1,0x9181,0x5140,0x9301,0x53C0,0x5280,0x9241,0x9601,0x56C0,0x5780,0x9741,0x5500,0x95C1,0x9481,0x5440,0x9C01,0x5CC0,0x5D80,0x9D41,0x5F00,0x9FC1,0x9E81,0x5E40,0x5A00,0x9AC1,0x9B81,0x5B40,0x9901,0x59C0,0x5880,0x9841,0x8801,0x48C0,0x4980,0x8941,0x4B00,0x8BC1,0x8A81,0x4A40,0x4E00,0x8EC1,0x8F81,0x4F40,0x8D01,0x4DC0,0x4C80,0x8C41,0x4400,0x84C1,0x8581,0x4540,0x8701,0x47C0,0x4680,0x8641,0x8201,0x42C0,0x4380,0x8341,0x4100,0x81C1,0x8081,0x4040]
            crc_hi=0xFF
            crc_lo=0xFF
            for w in data:
            index=crc_lo ^ ord(w)
            crc_val=crc_table[index]
            crc_temp=crc_val/256
            crc_val_low=crc_val - (crc_temp * 256)
            crc_lo = crc_val_low ^ crc_hi
            crc_hi = crc_temp
        crc=crc_hi*256 + crc_lo
        return crc

    
>>> calc (11010003000C)
SyntaxError: invalid syntax
>>> calc
<function calc at 0x02F02C70>
>>> calc 11 01 00 03 00 0C
SyntaxError: invalid syntax
>>> 

[buran]

do you NEED to write your own function? why not check available packages on PyPi. It look like at least 3 packages provide crc16 implementation

[Bokka]

do you NEED to write your own function? why not check available packages on PyPi. It look like at least 3 packages provide crc16 implementation

Yes, I prefer to have a function writed by me

[buran]

if you call it like this

calc ('11010003000C')

your function returns '3601'

One of the packages I testes - PyCRC calculates it as 3191

>>> from PyCRC.CRC16 import CRC16
>>> print CRC16().calculate('11010003000C')
3191
>>>

both not what you expect

CE9F