# Buggy code
def paste(self, im, box=None):
    """
    Paste a PIL image into the photo image.  Note that this can
    be very slow if the photo image is displayed.

    :param im: A PIL image. The size must match the target region.  If the
               mode does not match, the image is converted to the mode of
               the bitmap image.
    :param box: A 4-tuple defining the left, upper, right, and lower pixel
                coordinate. See :ref:`coordinate-system`. If None is given
                instead of a tuple, all of the image is assumed.
    """

    # convert to blittable
    im.load()
    image = im.im
    if image.isblock() and im.mode == self.__mode:
        block = image
    else:
        block = image.new_block(self.__mode, im.size)
        image.convert2(block, image)  # convert directly between buffers

    tk = self.__photo.tk

    try:
        tk.call("PyImagingPhoto", self.__photo, block.id)
    except tkinter.TclError:
        # activate Tkinter hook
        try:
            from . import _imagingtk

            try:
                if hasattr(tk, "interp"):
                    # Pypy is using a ffi cdata element
                    # (Pdb) self.tk.interp
                    #  <cdata 'Tcl_Interp *' 0x3061b50>
                    _imagingtk.tkinit(int(ffi.cast("uintptr_t", tk.interp)), 1)
                else:
                    _imagingtk.tkinit(tk.interpaddr(), 1)
            except AttributeError:
                _imagingtk.tkinit(id(tk), 0)
            tk.call("PyImagingPhoto", self.__photo, block.id)
        except (ImportError, AttributeError, tkinter.TclError):
            raise  # configuration problem; cannot attach to Tkinter


# Traceback (AttributeError)
Traceback (most recent call last):
File "test.py", line 1, in <module>
import PIL
File "/usr/lib/python3.6/site-packages/PIL/__init__.py", line 27, in <module>
__doc__ = __doc__.format(__version__)  # include version in docstring
AttributeError: 'NoneType' object has no attribute 'format'

# Fixed code
def paste(self, im, box=None):
    """
    Paste a PIL image into the photo image.  Note that this can
    be very slow if the photo image is displayed.

    :param im: A PIL image. The size must match the target region.  If the
               mode does not match, the image is converted to the mode of
               the bitmap image.
    :param box: A 4-tuple defining the left, upper, right, and lower pixel
                coordinate. See :ref:`coordinate-system`. If None is given
                instead of a tuple, all of the image is assumed.
    """

    # convert to blittable
    im.load()
    image = im.im
    if image.isblock() and im.mode == self.__mode:
        block = image
    else:
        block = image.new_block(self.__mode, im.size)
        image.convert2(block, image)  # convert directly between buffers

    tk = self.__photo.tk

    try:
        tk.call("PyImagingPhoto", self.__photo, block.id)
    except tkinter.TclError:
        # activate Tkinter hook
        try:
            from . import _imagingtk

            try:
                if hasattr(tk, "interp"):
                    # Required for PyPy, which always has CFFI installed
                    from cffi import FFI

                    ffi = FFI()

                    # PyPy is using an FFI CDATA element
                    # (Pdb) self.tk.interp
                    #  <cdata 'Tcl_Interp *' 0x3061b50>
                    _imagingtk.tkinit(int(ffi.cast("uintptr_t", tk.interp)), 1)
                else:
                    _imagingtk.tkinit(tk.interpaddr(), 1)
            except AttributeError:
                _imagingtk.tkinit(id(tk), 0)
            tk.call("PyImagingPhoto", self.__photo, block.id)
        except (ImportError, AttributeError, tkinter.TclError):
            raise  # configuration problem; cannot attach to Tkinter