How verify function implemented?

Question

I want to find how verify() function from Pillow library implemented. In a source code i found only this:

def verify(self):
    """
    Verifies the contents of a file. For data read from a file, this
    method attempts to determine if the file is broken, without
    actually decoding the image data.  If this method finds any
    problems, it raises suitable exceptions.  If you need to load
    the image after using this method, you must reopen the image
    file.
    """
    pass

Where i can find implementation?

(source code i found here: Pillow source code )

Answer 1

A comment on GitHub explains:

Image.[v]erify only checks the chunk checksums in png files, and is a no-op elsewhere.

So the short answer is that you already did find the default implementation which does absolutely nothing.

Except for PNG files , for which you can find the implementation in the PngImageFile.verify method:

    def verify(self):
        "Verify PNG file"

        if self.fp is None:
            raise RuntimeError("verify must be called directly after open")

        # back up to beginning of IDAT block
        self.fp.seek(self.tile[0][2] - 8)

        self.png.verify()
        self.png.close()

        self.fp = None

which in turn through self.png.verify() calls ChunkStream.verify :

    def verify(self, endchunk=b"IEND"):

        # Simple approach; just calculate checksum for all remaining
        # blocks.  Must be called directly after open.

        cids = []

        while True:
            cid, pos, length = self.read()
            if cid == endchunk:
                break
            self.crc(cid, ImageFile._safe_read(self.fp, length))
            cids.append(cid)

        return cids

More detailed source code breakdown

Your already quoted code for the verify method of the Image class shows that it by default does nothing:

class Image:

    ...

    def verify(self):
        """
        Verifies the contents of a file. For data read from a file, this
        method attempts to determine if the file is broken, without
        actually decoding the image data.  If this method finds any
        problems, it raises suitable exceptions.  If you need to load
        the image after using this method, you must reopen the image
        file.
        """
        pass

But in the case of PNG files the default verify method is overridden, as seen from the source code for the ImageFile class, which inherits from the Image class:

class ImageFile(Image.Image):
    "Base class for image file format handlers."

    ...

and the source code for the PNG plugin class PngImageFile which inherits from ImageFile :

##
# Image plugin for PNG images.

class PngImageFile(ImageFile.ImageFile):

    ...

and has this overridden implementation of verify :

    def verify(self):
        "Verify PNG file"

        if self.fp is None:
            raise RuntimeError("verify must be called directly after open")

        # back up to beginning of IDAT block
        self.fp.seek(self.tile[0][2] - 8)

        self.png.verify()
        self.png.close()

        self.fp = None

which in turn through self.png.verify() calls ChunkStream.verify :

    def verify(self, endchunk=b"IEND"):

        # Simple approach; just calculate checksum for all remaining
        # blocks.  Must be called directly after open.

        cids = []

        while True:
            cid, pos, length = self.read()
            if cid == endchunk:
                break
            self.crc(cid, ImageFile._safe_read(self.fp, length))
            cids.append(cid)

        return cids

through the PngStream class which doesn't override verify :

class PngStream(ChunkStream):

    ...