# Copyright 2008-2018 pydicom authors. See LICENSE file for details.
"""Handle alternate character sets for character strings."""
import codecs
import re
import warnings
from pydicom import compat, config
from pydicom.compat import in_py2
from pydicom.valuerep import PersonNameUnicode, text_VRs, TEXT_VR_DELIMS
# default encoding if no encoding defined - corresponds to ISO IR 6 / ASCII
default_encoding = "iso8859"
# Map DICOM Specific Character Set to python equivalent
python_encoding = {
# default character set for DICOM
'': default_encoding,
# alias for latin_1 too (iso_ir_6 exists as an alias to 'ascii')
'ISO_IR 6': default_encoding,
'ISO_IR 13': 'shift_jis',
# these also have iso_ir_1XX aliases in python 2.7
'ISO_IR 100': 'latin_1',
'ISO_IR 101': 'iso8859_2',
'ISO_IR 109': 'iso8859_3',
'ISO_IR 110': 'iso8859_4',
'ISO_IR 126': 'iso_ir_126', # Greek
'ISO_IR 127': 'iso_ir_127', # Arabic
'ISO_IR 138': 'iso_ir_138', # Hebrew
'ISO_IR 144': 'iso_ir_144', # Russian
'ISO_IR 148': 'iso_ir_148', # Turkish
'ISO_IR 166': 'iso_ir_166', # Thai
'ISO 2022 IR 6': 'iso8859', # alias for latin_1 too
'ISO 2022 IR 13': 'shift_jis',
'ISO 2022 IR 87': 'iso2022_jp',
'ISO 2022 IR 100': 'latin_1',
'ISO 2022 IR 101': 'iso8859_2',
'ISO 2022 IR 109': 'iso8859_3',
'ISO 2022 IR 110': 'iso8859_4',
'ISO 2022 IR 126': 'iso_ir_126',
'ISO 2022 IR 127': 'iso_ir_127',
'ISO 2022 IR 138': 'iso_ir_138',
'ISO 2022 IR 144': 'iso_ir_144',
'ISO 2022 IR 148': 'iso_ir_148',
'ISO 2022 IR 149': 'euc_kr',
'ISO 2022 IR 159': 'iso-2022-jp',
'ISO 2022 IR 166': 'iso_ir_166',
'ISO 2022 IR 58': 'iso_ir_58',
'ISO_IR 192': 'UTF8', # from Chinese example, 2008 PS3.5 Annex J p1-4
'GB18030': 'GB18030',
'ISO 2022 GBK': 'GBK', # from DICOM correction CP1234
'ISO 2022 58': 'GB2312', # from DICOM correction CP1234
'GBK': 'GBK', # from DICOM correction CP1234
}
# these encodings cannot be used with code extensions
# see DICOM Standard, Part 3, Table C.12-5
# and DICOM Standard, Part 5, Section 6.1.2.5.4, item d
STAND_ALONE_ENCODINGS = ('ISO_IR 192', 'GBK', 'GB18030')
# the escape character used to mark the start of escape sequences
ESC = b'\x1b'
# Map Python encodings to escape sequences as defined in PS3.3 in tables
# C.12-3 (single-byte) and C.12-4 (multi-byte character sets).
CODES_TO_ENCODINGS = {
ESC + b'(B': default_encoding, # used to switch to ASCII G0 code element
ESC + b'-A': 'latin_1',
ESC + b')I': 'shift_jis', # switches to ISO-IR 13
ESC + b'(J': 'shift_jis', # switches to ISO-IR 14 (shift_jis handles both)
ESC + b'$B': 'iso2022_jp',
ESC + b'-B': 'iso8859_2',
ESC + b'-C': 'iso8859_3',
ESC + b'-D': 'iso8859_4',
ESC + b'-F': 'iso_ir_126',
ESC + b'-G': 'iso_ir_127',
ESC + b'-H': 'iso_ir_138',
ESC + b'-L': 'iso_ir_144',
ESC + b'-M': 'iso_ir_148',
ESC + b'-T': 'iso_ir_166',
ESC + b'$)C': 'euc_kr',
ESC + b'$(D': 'iso-2022-jp',
ESC + b'$)A': 'iso_ir_58',
}
ENCODINGS_TO_CODES = {v: k for k, v in CODES_TO_ENCODINGS.items()}
ENCODINGS_TO_CODES['shift_jis'] = ESC + b')I'
# Multi-byte character sets except Korean are handled by Python.
# To decode them, the escape sequence shall be preserved in the input byte
# string, and will be removed during decoding by Python.
handled_encodings = ('iso2022_jp',
'iso-2022-jp',
'iso_ir_58')
def _encode_to_jis_x_0201(value, errors='strict'):
"""Convert a unicode string into JIS X 0201 byte string using shift_jis
encodings.
shift_jis is a superset of jis_x_0201. So we can regard the encoded value
as jis_x_0201 if it is single byte character.
Parameters
----------
value : text type
The unicode string as presented to the user.
errors : str
The behavior of a character which could not be encoded. If 'strict' is
passed, raise an UnicodeEncodeError. If any other value is passed,
non ISO IR 14 characters are replaced by the ASCII '?'.
Returns
-------
byte string
The encoded string. If some characters in value could not be encoded to
JIS X 0201, and `errors` is not set to 'strict', they are replaced to
'?'.
Raises
------
UnicodeEncodeError
If errors is set to 'strict' and `value` could not be encoded with
JIS X 0201.
"""
Encoder = codecs.getincrementalencoder('shift_jis')
encoder = Encoder()
# If errors is not strict, this function is used as fallback.
# In this case, we use only ISO IR 14 to encode given value
# without escape sequence.
if errors != 'strict' or value == '':
encoded = b''
for c in value:
try:
b = encoder.encode(c)
except UnicodeEncodeError as e:
b = b'?'
if len(b) != 1 or 0x80 <= ord(b):
b = b'?'
encoded += b
return encoded
encoded = encoder.encode(value[0])
if len(encoded) != 1:
raise UnicodeEncodeError(
'shift_jis', value, 0, len(value), 'illegal multibyte sequence')
msb = ord(encoded) & 0x80 # msb is 1 for ISO IR 13, 0 for ISO IR 14
for i, c in enumerate(value[1:], 1):
try:
b = encoder.encode(c)
except UnicodeEncodeError as e:
e.start = i
e.end = len(value)
raise e
if len(b) != 1 or ((ord(b) & 0x80) ^ msb) != 0:
character_set = 'ISO IR 14' if msb == 0 else 'ISO IR 13'
msg = 'Given character is out of {}'.format(character_set)
raise UnicodeEncodeError('shift_jis', value, i, len(value), msg)
encoded += b
return encoded
def _encode_to_jis_x_0208(value, errors='strict'):
"""Convert a unicode string into JIS X 0208 byte string using iso2022_jp
encodings.
The escape sequence which is located at the end of the encoded value has
to vary depending on the value 1 of SpecificCharacterSet. So we have to
trim it and append the correct escape sequence manually.
Parameters
----------
value : text type
The unicode string as presented to the user.
errors : str
The behavior of a character which could not be encoded. This value
is passed to errors argument of str.encode().
Returns
-------
byte string
The encoded string. If some characters in value could not be encoded to
JIS X 0208, it depends on the behavior of iso2022_jp encoder.
Raises
------
UnicodeEncodeError
If errors is set to 'strict' and `value` could not be encoded with
JIS X 0208.
"""
# If errors is not strict, this function is used as fallback.
# So keep the tail escape sequence of encoded for backward compatibility.
if errors != 'strict':
return value.encode('iso2022_jp', errors=errors)
Encoder = codecs.getincrementalencoder('iso2022-jp')
encoder = Encoder()
encoded = encoder.encode(value[0])
if encoded[:3] != ENCODINGS_TO_CODES['iso2022_jp']:
raise UnicodeEncodeError(
'iso2022_jp', value, 0, len(value),
'Given character is out of ISO IR 87')
for i, c in enumerate(value[1:], 1):
try:
b = encoder.encode(c)
except UnicodeEncodeError as e:
e.start = i
e.end = len(value)
raise e
if b[:3] == ENCODINGS_TO_CODES['iso8859']:
raise UnicodeEncodeError(
'iso2022_jp', value, i, len(value),
'Given character is out of ISO IR 87')
encoded += b
return encoded
def _get_escape_sequence_for_encoding(encoding, encoded=None):
""" Return an escape sequence corresponding to the given encoding. If
encoding is 'shift_jis', return 'ESC)I' or 'ESC(J' depending on the first
byte of encoded.
Parameters
----------
encoding : str
An encoding is used to specify an escape sequence.
encoded : bytes or str
The encoded value is used to chose an escape sequence if encoding is
'shift_jis'
Returns
-------
string
Escape sequence for encoded value.
"""
ESC_ISO_IR_14 = ESC + b'(J'
ESC_ISO_IR_13 = ESC + b')I'
if encoding == 'shift_jis':
if encoded is None:
return ESC_ISO_IR_14
if not in_py2:
first_byte = encoded[0]
else:
first_byte = ord(encoded[0])
if 0x80 <= first_byte:
return ESC_ISO_IR_13
return ESC_ISO_IR_14
return ENCODINGS_TO_CODES.get(encoding, b'')
# These encodings need escape sequence to handle alphanumeric characters.
need_tail_escape_sequence_encodings = ('iso2022_jp', 'iso-2022-jp')
custom_encoders = {
'shift_jis': _encode_to_jis_x_0201,
'iso2022_jp': _encode_to_jis_x_0208,
'iso-2022-jp': _encode_to_jis_x_0208
}
[docs]def decode_string(value, encodings, delimiters):
"""Convert a raw byte string into a unicode string using the given
list of encodings.
Parameters
----------
value : byte string
The raw string as encoded in the DICOM tag value.
encodings : list
The encodings needed to decode the string as a list of Python
encodings, converted from the encodings in Specific Character Set.
delimiters: set of int (Python 3) or characters (Python 2)
A set of characters or character codes, each of which resets the
encoding in `byte_str`.
Returns
-------
text type
The decoded unicode string. If the value could not be decoded,
and `config.enforce_valid_values` is not set, a warning is issued,
and the value is decoded using the first encoding with replacement
characters, resulting in data loss.
Raises
------
UnicodeDecodeError
If `config.enforce_valid_values` is set and `value` could not be
decoded with the given encodings.
"""
# shortcut for the common case - no escape sequences present
if ESC not in value:
first_encoding = encodings[0]
try:
return value.decode(first_encoding)
except LookupError:
if config.enforce_valid_values:
raise
warnings.warn(u"Unknown encoding '{}' - "
u"using default encoding instead"
.format(first_encoding))
first_encoding = default_encoding
return value.decode(first_encoding)
except UnicodeError:
if config.enforce_valid_values:
raise
warnings.warn(u"Failed to decode byte string with encoding '{}' - "
u"using replacement characters in decoded "
u"string".format(first_encoding))
return value.decode(first_encoding, errors='replace')
# Each part of the value that starts with an escape sequence is decoded
# separately. If it starts with an escape sequence, the
# corresponding encoding is used, otherwise (e.g. the first part if it
# does not start with an escape sequence) the first encoding.
# See PS3.5, 6.1.2.4 and 6.1.2.5 for the use of code extensions.
#
# The following regex splits the value into these parts, by matching
# the substring until the first escape character, and subsequent
# substrings starting with an escape character.
regex = b'(^[^\x1b]+|[\x1b][^\x1b]*)'
fragments = re.findall(regex, value)
# decode each byte string fragment with it's corresponding encoding
# and join them all together
return u''.join([_decode_fragment(fragment, encodings, delimiters)
for fragment in fragments])
def _decode_fragment(byte_str, encodings, delimiters):
"""Decode a byte string encoded with a single encoding.
If `byte_str` starts with an escape sequence, the encoding corresponding
to this sequence is used for decoding if present in `encodings`,
otherwise the first value in encodings.
If a delimiter occurs inside the string, it resets the encoding to the
first encoding in case of single-byte encodings.
Parameters
----------
byte_str : bytes
The raw string to be decoded.
encodings: list of str
The list of Python encodings as converted from the values in the
Specific Character Set tag.
delimiters: set of int (Python 3) or characters (Python 2)
A set of characters or character codes, each of which resets the
encoding in `byte_str`.
Returns
-------
text type
The decoded unicode string. If the value could not be decoded,
and `config.enforce_valid_values` is not set, a warning is issued,
and the value is decoded using the first encoding with replacement
characters, resulting in data loss.
Raises
------
UnicodeDecodeError
If `config.enforce_valid_values` is set and `value` could not be
decoded with the given encodings.
Reference
---------
* DICOM Standard Part 5, Sections 6.1.2.4 and 6.1.2.5
* DICOM Standard Part 3, Anex C.12.1.1.2
"""
try:
if byte_str.startswith(ESC):
return _decode_escaped_fragment(byte_str, encodings, delimiters)
# no escape sequence - use first encoding
return byte_str.decode(encodings[0])
except UnicodeError:
if config.enforce_valid_values:
raise
warnings.warn(u"Failed to decode byte string with encodings: {} - "
u"using replacement characters in decoded "
u"string".format(', '.join(encodings)))
return byte_str.decode(encodings[0], errors='replace')
def _decode_escaped_fragment(byte_str, encodings, delimiters):
"""Decodes a byte string starting with an escape sequence.
See `_decode_fragment` for parameter description and more information.
"""
# all 4-character escape codes start with one of two character sets
seq_length = 4 if byte_str.startswith((b'\x1b$(', b'\x1b$)')) else 3
encoding = CODES_TO_ENCODINGS.get(byte_str[:seq_length], '')
if encoding in encodings or encoding == default_encoding:
if encoding in handled_encodings:
# Python strips the escape sequences for this encoding.
# Any delimiters must be handled correctly by `byte_str`.
return byte_str.decode(encoding)
else:
# Python doesn't know about the escape sequence -
# we have to strip it before decoding
byte_str = byte_str[seq_length:]
# If a delimiter occurs in the string, it resets the encoding.
# The following returns the first occurrence of a delimiter in
# the byte string, or None if it does not contain any.
index = next((index for index, ch in enumerate(byte_str)
if ch in delimiters), None)
if index is not None:
# the part of the string after the first delimiter
# is decoded with the first encoding
return (byte_str[:index].decode(encoding) +
byte_str[index:].decode(encodings[0]))
# No delimiter - use the encoding defined by the escape code
return byte_str.decode(encoding)
# unknown escape code - use first encoding
msg = u"Found unknown escape sequence in encoded string value"
if config.enforce_valid_values:
raise ValueError(msg)
warnings.warn(msg + u" - using encoding {}".format(encodings[0]))
return byte_str.decode(encodings[0], errors='replace')
[docs]def encode_string(value, encodings):
"""Convert a unicode string into a byte string using the given
list of encodings.
Parameters
----------
value : text type
The unicode string as presented to the user.
encodings : list
The encodings needed to encode the string as a list of Python
encodings, converted from the encodings in Specific Character Set.
Returns
-------
byte string
The encoded string. If the value could not be encoded with any of
the given encodings, and `config.enforce_valid_values` is not set, a
warning is issued, and the value is encoded using the first
encoding with replacement characters, resulting in data loss.
Raises
------
UnicodeEncodeError
If `config.enforce_valid_values` is set and `value` could not be
encoded with the given encodings.
"""
for i, encoding in enumerate(encodings):
try:
encoded = _encode_string_impl(value, encoding)
if i > 0 and encoding not in handled_encodings:
escape_sequence = _get_escape_sequence_for_encoding(
encoding, encoded=encoded)
encoded = escape_sequence + encoded
if encoding in need_tail_escape_sequence_encodings:
encoded += _get_escape_sequence_for_encoding(encodings[0])
return encoded
except UnicodeError:
continue
else:
# if we have more than one encoding, we retry encoding by splitting
# `value` into chunks that can be encoded with one of the encodings
if len(encodings) > 1:
try:
return _encode_string_parts(value, encodings)
except ValueError:
pass
# all attempts failed - raise or warn and encode with replacement
# characters
if config.enforce_valid_values:
# force raising a valid UnicodeEncodeError
value.encode(encodings[0])
warnings.warn("Failed to encode value with encodings: {} - using "
"replacement characters in encoded string"
.format(', '.join(encodings)))
return _encode_string_impl(value, encodings[0], errors='replace')
def _encode_string_parts(value, encodings):
"""Convert a unicode string into a byte string using the given
list of encodings.
This is invoked if `encode_string` failed to encode `value` with a single
encoding. We try instead to use different encodings for different parts
of the string, using the encoding that can encode the longest part of
the rest of the string as we go along.
Parameters
----------
value : text type
The unicode string as presented to the user.
encodings : list
The encodings needed to encode the string as a list of Python
encodings, converted from the encodings in Specific Character Set.
Returns
-------
byte string
The encoded string, including the escape sequences needed to switch
between different encodings.
Raises
------
ValueError
If `value` could not be encoded with the given encodings.
"""
encoded = bytearray()
unencoded_part = value
best_encoding = None
while unencoded_part:
# find the encoding that can encode the longest part of the rest
# of the string still to be encoded
max_index = 0
for encoding in encodings:
try:
_encode_string_impl(unencoded_part, encoding)
# if we get here, the whole rest of the value can be encoded
best_encoding = encoding
max_index = len(unencoded_part)
break
except UnicodeError as e:
if e.start > max_index:
# e.start is the index of first character failed to encode
max_index = e.start
best_encoding = encoding
# none of the given encodings can encode the first character - give up
if max_index == 0:
raise ValueError("None of the given encodings can encode the "
"first character")
# encode the part that can be encoded with the found encoding
encoded_part = _encode_string_impl(unencoded_part[:max_index],
best_encoding)
if best_encoding not in handled_encodings:
encoded += _get_escape_sequence_for_encoding(
best_encoding, encoded=encoded_part)
encoded += encoded_part
# set remaining unencoded part of the string and handle that
unencoded_part = unencoded_part[max_index:]
# unencoded_part is empty - we are done, return the encoded string
if best_encoding in need_tail_escape_sequence_encodings:
encoded += _get_escape_sequence_for_encoding(encodings[0])
return encoded
def _encode_string_impl(value, encoding, errors='strict'):
"""Convert a unicode string into a byte string. If given encoding is in
custom_encoders, use a corresponding custom_encoder. If given encoding
is not in custom_encoders, use a corresponding python handled encoder.
"""
if encoding in custom_encoders:
return custom_encoders[encoding](value, errors=errors)
else:
return value.encode(encoding, errors=errors)
# DICOM PS3.5-2008 6.1.1 (p 18) says:
# default is ISO-IR 6 G0, equiv to common chr set of ISO 8859 (PS3.5 6.1.2.1)
# (0008,0005) value 1 can *replace* the default encoding...
# for VRs of SH, LO, ST, LT, PN and UT (PS3.5 6.1.2.3)...
# with a single-byte character encoding
# if (0008,0005) is multi-valued, then value 1 (or default if blank)...
# is used until code extension escape sequence is hit,
# which can be at start of string, or after CR/LF, FF, or
# in Person Name PN, after ^ or =
# NOTE also that 7.5.3 SEQUENCE INHERITANCE states that if (0008,0005)
# is not present in a sequence item then it is inherited from its parent.
[docs]def convert_encodings(encodings):
"""Converts DICOM encodings into corresponding python encodings.
Handles some common spelling mistakes and issues a warning in this case.
Handles stand-alone encodings: if they are the first encodings,
additional encodings are ignored, if they are not the first encoding,
they are ignored. In both cases, a warning is issued.
Invalid encodings are replaced with the default encoding with a
respective warning issued, if `config.enforce_valid_values` is `False`,
otherwise an exception is raised.
Parameters
----------
encodings : list of str
The list of encodings as read from Specific Character Set.
Returns
-------
list of str
The list of Python encodings corresponding to the DICOM encodings.
If an encoding is already a Python encoding, it is returned unchanged.
Encodings with common spelling errors are replaced by the correct
encoding, and invalid encodings are replaced with the default
encoding if `config.enforce_valid_values` is `False`.
Raises
------
LookupError
In case of an invalid encoding that could not be corrected if
`config.enforce_valid_values` is set.
"""
# If a list if passed, we don't want to modify the list in place so copy it
encodings = encodings[:]
if isinstance(encodings, compat.string_types):
encodings = [encodings]
elif not encodings[0]:
encodings[0] = 'ISO_IR 6'
py_encodings = []
for encoding in encodings:
try:
py_encodings.append(python_encoding[encoding])
except KeyError:
py_encodings.append(
_python_encoding_for_corrected_encoding(encoding))
if len(encodings) > 1:
py_encodings = _handle_illegal_standalone_encodings(encodings,
py_encodings)
return py_encodings
def _python_encoding_for_corrected_encoding(encoding):
"""Try to replace the given invalid encoding with a valid encoding by
checking for common spelling errors, and return the correct Python
encoding for that encoding. Otherwise check if the
encoding is already a valid Python encoding, and return that. If both
attempts fail, return the default encoding.
Issue a warning for the invalid encoding except for the case where it is
already converted.
"""
# standard encodings
patched = None
if re.match('^ISO[^_]IR', encoding) is not None:
patched = 'ISO_IR' + encoding[6:]
# encodings with code extensions
elif re.match('^(?=ISO.2022.IR.)(?!ISO 2022 IR )',
encoding) is not None:
patched = 'ISO 2022 IR ' + encoding[12:]
if patched:
# handle encoding patched for common spelling errors
try:
py_encoding = python_encoding[patched]
_warn_about_invalid_encoding(encoding, patched)
return py_encoding
except KeyError:
_warn_about_invalid_encoding(encoding)
return default_encoding
# fallback: assume that it is already a python encoding
try:
codecs.lookup(encoding)
return encoding
except LookupError:
_warn_about_invalid_encoding(encoding)
return default_encoding
def _warn_about_invalid_encoding(encoding, patched_encoding=None):
"""Issue a warning for the given invalid encoding.
If patched_encoding is given, it is mentioned as the
replacement encoding, other the default encoding.
If no replacement encoding is given, and config.enforce_valid_values
is set, LookupError is raised.
"""
if patched_encoding is None:
if config.enforce_valid_values:
raise LookupError(
"Unknown encoding '{}'".format(encoding))
msg = ("Unknown encoding '{}' - using default encoding "
"instead".format(encoding))
else:
msg = ("Incorrect value for Specific Character Set "
"'{}' - assuming '{}'".format(encoding, patched_encoding))
warnings.warn(msg, stacklevel=2)
def _handle_illegal_standalone_encodings(encodings, py_encodings):
"""Check for stand-alone encodings in multi-valued encodings.
If the first encoding is a stand-alone encoding, the rest of the
encodings is removed. If any other encoding is a stand-alone encoding,
it is removed from the encodings.
"""
if encodings[0] in STAND_ALONE_ENCODINGS:
warnings.warn("Value '{}' for Specific Character Set does not "
"allow code extensions, ignoring: {}"
.format(encodings[0], ', '.join(encodings[1:])),
stacklevel=2)
py_encodings = py_encodings[:1]
else:
for i, encoding in reversed(list(enumerate(encodings[1:]))):
if encoding in STAND_ALONE_ENCODINGS:
warnings.warn(
"Value '{}' cannot be used as code extension, "
"ignoring it".format(encoding),
stacklevel=2)
del py_encodings[i + 1]
return py_encodings
[docs]def decode(data_element, dicom_character_set):
"""Apply the DICOM character encoding to the data element
data_element -- DataElement instance containing a value to convert
dicom_character_set -- the value of Specific Character Set (0008,0005),
which may be a single value,
a multiple value (code extension), or
may also be '' or None.
If blank or None, ISO_IR 6 is used.
"""
if not dicom_character_set:
dicom_character_set = ['ISO_IR 6']
encodings = convert_encodings(dicom_character_set)
# decode the string value to unicode
# PN is special case as may have 3 components with different chr sets
if data_element.VR == "PN":
if not in_py2:
if data_element.VM == 1:
data_element.value = data_element.value.decode(encodings)
else:
data_element.value = [
val.decode(encodings) for val in data_element.value
]
else:
if data_element.VM == 1:
data_element.value = PersonNameUnicode(data_element.value,
encodings)
else:
data_element.value = [
PersonNameUnicode(value, encodings)
for value in data_element.value
]
if data_element.VR in text_VRs:
# You can't re-decode unicode (string literals in py3)
if data_element.VM == 1:
if isinstance(data_element.value, compat.text_type):
return
data_element.value = decode_string(data_element.value, encodings,
TEXT_VR_DELIMS)
else:
output = list()
for value in data_element.value:
if isinstance(value, compat.text_type):
output.append(value)
else:
output.append(decode_string(value, encodings,
TEXT_VR_DELIMS))
data_element.value = output