# Buggy code
def save_as(self, filename, write_like_original=True):
    """Write the :class:`Dataset` to `filename`.

    Saving requires that the ``Dataset.is_implicit_VR`` and
    ``Dataset.is_little_endian`` attributes exist and are set
    appropriately. If ``Dataset.file_meta.TransferSyntaxUID`` is present
    then it should be set to a consistent value to ensure conformance.

    **Conformance with DICOM File Format**

    If `write_like_original` is ``False``, the :class:`Dataset` will be
    stored in the :dcm:`DICOM File Format <part10/chapter_7.html>`. To do
    so requires that the ``Dataset.file_meta`` attribute
    exists and contains a :class:`Dataset` with the required (Type 1) *File
    Meta Information Group* elements (see
    :func:`~pydicom.filewriter.dcmwrite` and
    :func:`~pydicom.filewriter.write_file_meta_info` for more information).

    If `write_like_original` is ``True`` then the :class:`Dataset` will be
    written as is (after minimal validation checking) and may or may not
    contain all or parts of the *File Meta Information* (and hence may or
    may not be conformant with the DICOM File Format).

    Parameters
    ----------
    filename : str or PathLike or file-like
        Name of file or the file-like to write the new DICOM file to.
    write_like_original : bool, optional
        If ``True`` (default), preserves the following information from
        the :class:`Dataset` (and may result in a non-conformant file):

        - preamble -- if the original file has no preamble then none will
          be written.
        - file_meta -- if the original file was missing any required *File
          Meta Information Group* elements then they will not be added or
          written.
          If (0002,0000) *File Meta Information Group Length* is present
          then it may have its value updated.
        - seq.is_undefined_length -- if original had delimiters, write them
          now too, instead of the more sensible length characters
        - is_undefined_length_sequence_item -- for datasets that belong to
          a sequence, write the undefined length delimiters if that is
          what the original had.

        If ``False``, produces a file conformant with the DICOM File
        Format, with explicit lengths for all elements.

    See Also
    --------
    pydicom.filewriter.write_dataset
        Write a :class:`Dataset` to a file.
    pydicom.filewriter.write_file_meta_info
        Write the *File Meta Information Group* elements to a file.
    pydicom.filewriter.dcmwrite
        Write a DICOM file from a :class:`FileDataset` instance.
    """
    # Ensure is_little_endian and is_implicit_VR are set
    if None in (self.is_little_endian, self.is_implicit_VR):
        has_tsyntax = False
        try:
            tsyntax = self.file_meta.TransferSyntaxUID
            if not tsyntax.is_private:
                self.is_little_endian = tsyntax.is_little_endian
                self.is_implicit_VR = tsyntax.is_implicit_VR
                has_tsyntax = True
        except AttributeError:
            pass

        if not has_tsyntax:
            raise AttributeError(
                "'{0}.is_little_endian' and '{0}.is_implicit_VR' must be "
                "set appropriately before saving.".format(self.__class__.__name__)
            )

    # Try and ensure that `is_undefined_length` is set correctly
    try:
        tsyntax = self.file_meta.TransferSyntaxUID
        if not tsyntax.is_private:
            self["PixelData"].is_undefined_length = tsyntax.is_compressed
    except (AttributeError, KeyError):
        pass

    pydicom.dcmwrite(filename, self, write_like_original)


# Traceback (TypeError)
TypeError: With tag (0018, 9306) got exception: string indices must be integers
Traceback (most recent call last):
File "/Users/arzt/src/pydicom/pydicom/tag.py", line 30, in tag_in_exception
yield
File "/Users/arzt/src/pydicom/pydicom/filewriter.py", line 555, in write_dataset
write_data_element(fp, dataset.get_item(tag), dataset_encoding)
File "/Users/arzt/src/pydicom/pydicom/filewriter.py", line 482, in write_data_element
writer_function(buffer, data_element, writer_param)
File "/Users/arzt/src/pydicom/pydicom/filewriter.py", line 222, in write_numbers
endianChar = '><' [fp.is_little_endian]
TypeError: string indices must be integers

# Fixed code
def save_as(self, filename, write_like_original=True):
    """Write the :class:`Dataset` to `filename`.

    Wrapper for pydicom.filewriter.dcmwrite, passing this dataset to it.
    See documentation for that function for details.

    See Also
    --------
    pydicom.filewriter.dcmwrite
        Write a DICOM file from a :class:`FileDataset` instance.
    """
    pydicom.dcmwrite(filename, self, write_like_original)