CODEWITHSUNDEEP
pythonexceptionwrapperassert
mtoloo
mtoloo

Reputation: 1875

Handle C assertions from python

I used the following python code to compress a dicom file using GDCM:

    import gdcm

    reader = gdcm.PixmapReader()
    reader.SetFileName(str(source))
    if not reader.Read():
        raise BaseException("Could not read (pixmap) %s" % source)
    image = reader.GetPixmap()
    change = gdcm.ImageChangeTransferSyntax()
    change.SetForce(False)
    change.SetCompressIconImage(False)
    transfer_syntax = gdcm.TransferSyntax(gdcm.TransferSyntax.JPEG2000Lossless)
    change.SetTransferSyntax(transfer_syntax)
    change.SetInput(image)
    if not change.Change():
        raise BaseException("Could not change the Transfer Syntax: ")
    ....

In the line change.Change(), there's an assertion in GDCM source which may faile:

Assertion `((fragment_size + 1)/2 ) * 2 == ((image_height * image_width * numcomps * (bitsallocated/8) + 1)/ 2 )* 2' failed.

Unfortunately python process would be killed in the case of assertion failure at GDCM. Is there a way to handle such assertions (without having checked the conditions at python before calling change.Change())?

Upvotes: 0

Views: 131

Answers (2)

mtoloo
mtoloo

Reputation: 1875

Reluctantly I checked the Dicom integrity using pydicom before compressing Dicom:

def check_dicom(dicom_file):
    p = dicom.read_file(dicom_file)
    assert p.SamplesPerPixel in (1, 3)
    if p.BitsAllocated % 8 != 0:
        return False

    # assert( ((fragment_size + 1)/2 ) * 2 == ((image_height * image_width * numcomps * (bitsallocated/8) + 1)/ 2 )* 2 );
    left = ((len(p.PixelData) + 1)/2 ) * 2
    right = ((p.Rows * p.Columns * p.SamplesPerPixel * (p.BitsAllocated/8) + 1)/ 2 )* 2
    if left != right:
        raise BaseException("DICOM attributes are in conflict with pixel data size")
    return True

Upvotes: 0

Gribouillis
Gribouillis

Reputation: 2220

A way to handle this is to start a child process to call the C library, then raise an exception if the child process dies because of a C assert statement.

Upvotes: 1

Related Questions