Translating VB code into Python

Question

I have the following VB function, converted from a German Excel macro:

Function GetChecksumme(identNr As Integer) As BitArray 
    Dim Z1 As Integer ' {Hilfsz„hler 1}
    Dim Checksumme As New BitArray(27)
    Dim DoCoZahl As Long
    Dim Result As New BitArray(6)

    DoCoZahl = identNr
    'Zeit fuer diesen Schritt starten:}
    'Checksumme berechnen:}
    'False = logisch 0, True = logisch 1}
    '1. Schritt: Das Array 'CheckSumme' mit 26 Nullen auffuellen:}
    For Z1 = 1 To 26
        Checksumme(Z1) = False
    Next Z1
    '2. Schritt: DotCode-Zahl in duale Darstellung umrechnen und}
    'links von den rechten 6 Nullen einschreiben:}
    Z1 = 21
    Do While DoCoZahl > 0
        Z1 = Z1 - 1
        If (DoCoZahl Mod 2) = 0 Then
            Checksumme(Z1) = False
        End If
        If (DoCoZahl Mod 2) = 1 Then
            Checksumme(Z1) = True
        End If
        DoCoZahl = DoCoZahl \ 2
    Loop
    '3. Schritt: Solange XOR-Operation durchfhren, bis}
    'die Check-Summe ermittelt ist:}
    Do
        'Den ersten '1er' von links suchen:}
        Z1 = 0
        Do
            Z1 = Z1 + 1
        Loop Until ((Checksumme(Z1) = True) Or (Z1 > 20))
        'Ab dieser Stelle mit Maske 1 0 0 0 1 1 1 logisch XOR-verknpfen:}
        'Bit mit 1 XOR-verknpfen -> Ergebnis ist das negierte Bit.}
        'Bit mit 0 XOR-verknpfen -> Ergebnis ist das Bit.}
        If Z1 <= 20 Then
            Checksumme(Z1) = Not Checksumme(Z1)
            Checksumme(Z1 + 4) = Not Checksumme(Z1 + 4)
            Checksumme(Z1 + 5) = Not Checksumme(Z1 + 5)
            Checksumme(Z1 + 6) = Not Checksumme(Z1 + 6)
        End If
    Loop Until Z1 >= 20
    'Zeit fr diesen Schritt stoppen:}


    Result(0) = Checksumme(26)
    Result(1) = Checksumme(25)
    Result(2) = Checksumme(24)
    Result(3) = Checksumme(23)
    Result(4) = Checksumme(22)
    Result(5) = Checksumme(21)

    Return result

End Function

I've been asked to convert it for an in house project. I started by trying to convert it to python (my preferred language), so I could better understand the calculation:

def getChecksum(identNr, checksumNr=None):
    if not 0 <= checksumNr <= 5:
        raise ValueError()

    checksum = [False] * 27
    z1 = 20
    doCoZahl = identNr

    while doCoZahl > 0:
        checksum[z1] = doCoZahl & 1 == 1
        z1 -= 1
        doCoZahl >>= 2

    while z1 > 20:
        z1 = 0
        while (not checksum[z1]) or z1 <= 20:
            z1 += 1

        if z1 <= 20:
             Checksumme[z1] = not Checksumme[Z1]
             Checksumme[z1 + 4] = not Checksumme[Z1 + 4]
             Checksumme[z1 + 5] = not Checksumme[Z1 + 5]
             Checksumme[z1 + 6] = not Checksumme[Z1 + 6]

    return tuple(checksum[-1:-7:-1])

The problem is that python returns (False, False, False, False, False, False), no matter what input I give it. For instance, in VB:

GetChecksumme | Value (VB)
--------------+-----------
1             | TTTFFF
2             | FTTTFF

There's probably a simple mistake somewhere, but I can't see it.

PM 2Ring · Accepted Answer · 2016-04-18 15:41:39Z

1

You never enter the final while loop.

z1 starts at 20, it (possibly) gets reduced in the while doCoZahl > 0: loop, so when you hit while z1 > 20: z1 is <= 20.

Sorry, I don't know VB. I can kind of read that VB code, but not well enough to offer a faithful translation.

answered Apr 18, 2016 at 15:41

PM 2Ring

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