def write_sequence_item(fp: DicomIO, dataset: Dataset,
encodings: List[str]) -> None:
"""Write a `dataset` in a sequence to the file-like `fp`.
This is similar to writing a data_element, but with a specific tag for
Sequence Item.
See DICOM Standard, Part 5, :dcm:`Section 7.5<sect_7.5.html>`.
Parameters
----------
fp : file-like
The file-like to write the encoded data to.
dataset : Dataset
The :class:`Dataset<pydicom.dataset.Dataset>` to write to `fp`.
encodings : list of str
The character encodings to use on text values.
"""
fp.write_tag(ItemTag) # marker for start of Sequence Item
length_location = fp.tell() # save location for later.
# will fill in real value later if not undefined length
fp.write_UL(0xffffffff)
write_dataset(fp, dataset, parent_encoding=encodings)
if getattr(dataset, "is_undefined_length_sequence_item", False):
fp.write_tag(ItemDelimiterTag)
fp.write_UL(0) # 4-bytes 'length' field for delimiter item
else: # we will be nice and set the lengths for the reader of this file
location = fp.tell()
fp.seek(length_location)
fp.write_UL(location - length_location - 4) # 4 is length of UL
fp.seek(location) # ready for next data_element
def write_dataset(
fp: DicomIO,
dataset: Dataset,
parent_encoding: Union[str, List[str]] = default_encoding) -> int:
"""Write a Dataset dictionary to the file. Return the total length written.
"""
_harmonize_properties(dataset, fp)
if None in (dataset.is_little_endian, dataset.is_implicit_VR):
name = dataset.__class__.__name__
raise AttributeError(
f"'{name}.is_little_endian' and '{name}.is_implicit_VR' must "
f"be set appropriately before saving")
if not dataset.is_original_encoding:
dataset = correct_ambiguous_vr(dataset, fp.is_little_endian)
dataset_encoding = cast(
Union[None, str, List[str]],
dataset.get('SpecificCharacterSet', parent_encoding))
fpStart = fp.tell()
# data_elements must be written in tag order
tags = sorted(dataset.keys())
for tag in tags:
# do not write retired Group Length (see PS3.5, 7.2)
if tag.element == 0 and tag.group > 6:
continue
with tag_in_exception(tag):
write_data_element(fp, dataset.get_item(tag), dataset_encoding)
return fp.tell() - fpStart
