def data_element_generator(fp,
is_implicit_VR,
is_little_endian,
stop_when=None,
defer_size=None):
""":return: (tag, VR, length, value, value_tell,
is_implicit_VR, is_little_endian)
"""
if is_little_endian:
endian_chr = "<"
else:
endian_chr = ">"
if is_implicit_VR:
element_struct = Struct(endian_chr + "HHL")
else: # Explicit VR
# tag, VR, 2-byte length (or 0 if special VRs)
element_struct = Struct(endian_chr + "HH2sH")
extra_length_struct = Struct(endian_chr + "L") # for special VRs
extra_length_unpack = extra_length_struct.unpack # for lookup speed
# Make local variables so have faster lookup
fp_read = fp.read
fp_tell = fp.tell
element_struct_unpack = element_struct.unpack
while True:
# Read tag, VR, length, get ready to read value
bytes_read = fp_read(8)
if len(bytes_read) < 8:
raise StopIteration # at end of file
if is_implicit_VR:
# must reset VR each time; could have set last iteration (e.g. SQ)
VR = None
group, elem, length = element_struct_unpack(bytes_read)
else: # explicit VR
group, elem, VR, length = element_struct_unpack(bytes_read)
if VR in extra_length_VRs_b:
bytes_read = fp_read(4)
length = extra_length_unpack(bytes_read)[0]
# Positioned to read the value, but may not want to -- check stop_when
value_tell = fp_tell()
if stop_when is not None:
if stop_when(group, elem):
rewind_length = 8
if not is_implicit_VR and VR in extra_length_VRs_b:
rewind_length += 4
fp.seek(value_tell - rewind_length)
raise StopIteration
# Reading the value
# First case (most common): reading a value with a defined length
if length != 0xFFFFFFFF:
if defer_size is not None and length > defer_size:
# Flag as deferred by setting value to None, and skip bytes
value = None
fp.seek(fp_tell() + length)
else:
value = fp_read(length)
# import pdb;pdb.set_trace()
yield ((group, elem), VR, length, value, value_tell)
# Second case: undefined length - must seek to delimiter,
# unless is SQ type, in which case is easier to parse it, because
# undefined length SQs and items of undefined lengths can be nested
# and it would be error-prone to read to the correct outer delimiter
else:
# Try to look up type to see if is a SQ
# if private tag, won't be able to look it up in dictionary,
# in which case just ignore it and read the bytes unless it is
# identified as a Sequence
if VR is None:
try:
VR = dictionaryVR(tag)
except KeyError:
# Look ahead to see if it consists of items and is thus a SQ
next_tag = TupleTag(unpack(endian_chr + "HH", fp_read(4)))
# Rewind the file
fp.seek(fp_tell() - 4)
if next_tag == ItemTag:
VR = b'SQ'
if VR == b'SQ':
yield ((group, elem), VR, length, None, value_tell)
# seq = read_sequence(fp, is_implicit_VR,
# is_little_endian, length, encoding)
# yield DataElement(tag, VR, seq, value_tell,
# is_undefined_length=True)
else:
raise NotImplementedError(
"This reader does not handle undefined length except for SQ"
)
from pydicom.fileio.fileutil import read_undefined_length_value
delimiter = SequenceDelimiterTag
value = read_undefined_length_value(fp, is_little_endian,
delimiter, defer_size)
yield ((group, elem), VR, length, value, value_tell)
def data_element_generator(fp,
is_implicit_VR,
is_little_endian,
stop_when=None,
defer_size=None):
""":return: (tag, VR, length, value, value_tell,
is_implicit_VR, is_little_endian)
"""
if is_little_endian:
endian_chr = "<"
else:
endian_chr = ">"
if is_implicit_VR:
element_struct = Struct(endian_chr + "HHL")
else: # Explicit VR
# tag, VR, 2-byte length (or 0 if special VRs)
element_struct = Struct(endian_chr + "HH2sH")
extra_length_struct = Struct(endian_chr + "L") # for special VRs
extra_length_unpack = extra_length_struct.unpack # for lookup speed
# Make local variables so have faster lookup
fp_read = fp.read
fp_tell = fp.tell
element_struct_unpack = element_struct.unpack
defer_size = size_in_bytes(defer_size)
while True:
# Read tag, VR, length, get ready to read value
bytes_read = fp_read(8)
if len(bytes_read) < 8:
raise StopIteration # at end of file
if is_implicit_VR:
# must reset VR each time; could have set last iteration (e.g. SQ)
VR = None
group, elem, length = element_struct_unpack(bytes_read)
else: # explicit VR
group, elem, VR, length = element_struct_unpack(bytes_read)
if VR in extra_length_VRs_b:
bytes_read = fp_read(4)
length = extra_length_unpack(bytes_read)[0]
# Positioned to read the value, but may not want to -- check stop_when
value_tell = fp_tell()
if stop_when is not None:
if stop_when(group, elem):
rewind_length = 8
if not is_implicit_VR and VR in extra_length_VRs_b:
rewind_length += 4
fp.seek(value_tell - rewind_length)
raise StopIteration
# Reading the value
# First case (most common): reading a value with a defined length
if length != 0xFFFFFFFF:
if defer_size is not None and length > defer_size:
# Flag as deferred by setting value to None, and skip bytes
value = None
fp.seek(fp_tell() + length)
else:
value = fp_read(length)
# import pdb;pdb.set_trace()
yield ((group, elem), VR, length, value, value_tell)
# Second case: undefined length - must seek to delimiter,
# unless is SQ type, in which case is easier to parse it, because
# undefined length SQs and items of undefined lengths can be nested
# and it would be error-prone to read to the correct outer delimiter
else:
# Try to look up type to see if is a SQ
# if private tag, won't be able to look it up in dictionary,
# in which case just ignore it and read the bytes unless it is
# identified as a Sequence
if VR is None:
try:
VR = dictionary_VR(tag)
except KeyError:
# Look ahead to see if it consists of items and
# is thus a SQ
next_tag = TupleTag(unpack(endian_chr + "HH", fp_read(4)))
# Rewind the file
fp.seek(fp_tell() - 4)
if next_tag == ItemTag:
VR = b'SQ'
if VR == b'SQ':
yield ((group, elem), VR, length, None, value_tell)
# seq = read_sequence(fp, is_implicit_VR,
# is_little_endian, length, encoding)
# yield DataElement(tag, VR, seq, value_tell,
# is_undefined_length=True)
else:
raise NotImplementedError("This reader does not handle "
"undefined length except for SQ")
from pydicom.fileio.fileutil import read_undefined_length_value
delimiter = SequenceDelimiterTag
value = read_undefined_length_value(fp, is_little_endian,
delimiter, defer_size)
yield ((group, elem), VR, length, value, value_tell)