def parse_json(json, symbol_table=None):
"""Parses the given json encoded string into a list of top-level objects found.
The parser accepts both blank lines and comment lines (those beginning with optional whitespace
followed by the '#' character) as well as more than one top-level JSON object.
The parse also supports a simple protocol for serialized types that have an `_asdict` method.
This includes `namedtuple` subtypes as well as any custom class with an `_asdict` method defined;
see :class:`pants.engine.exp.serializable.Serializable`.
:param string json: A json encoded document with extra support for blank lines, comments and
multiple top-level objects.
:returns: A list of decoded json data.
:rtype: list
:raises: :class:`ParseError` if there were any problems encountered parsing the given `json`.
"""
decoder = JSONDecoder(encoding='UTF-8',
object_hook=_get_decoder(symbol_table),
strict=True)
# Strip comment lines and blank lines, which we allow, but preserve enough information about the
# stripping to constitute a reasonable error message that can be used to find the portion of the
# JSON document containing the error.
def non_comment_line(l):
stripped = l.lstrip()
return stripped if (stripped
and not stripped.startswith('#')) else None
offset = 0
objects = []
while True:
lines = json[offset:].splitlines()
if not lines:
break
# Strip whitespace and comment lines preceding the next JSON object.
while True:
line = non_comment_line(lines[0])
if not line:
comment_line = lines.pop(0)
offset += len(comment_line) + 1
elif line.startswith('{') or line.startswith('['):
# Account for leading space in this line that starts off the JSON object.
offset += len(lines[0]) - len(line)
break
else:
raise ParseError('Unexpected json line:\n{}'.format(lines[0]))
lines = json[offset:].splitlines()
if not lines:
break
# Prepare the JSON blob for parsing - strip blank and comment lines recording enough information
# To reconstitute original offsets after the parse.
comment_lines = []
non_comment_lines = []
for line_number, line in enumerate(lines):
if non_comment_line(line):
non_comment_lines.append(line)
else:
comment_lines.append((line_number, line))
data = '\n'.join(non_comment_lines)
try:
obj, idx = decoder.raw_decode(data)
objects.append(obj)
if idx >= len(data):
break
offset += idx
# Add back in any parsed blank or comment line offsets.
parsed_line_count = len(data[:idx].splitlines())
for line_number, line in comment_lines:
if line_number >= parsed_line_count:
break
offset += len(line) + 1
parsed_line_count += 1
except ValueError as e:
json_lines = data.splitlines()
col_width = len(str(len(json_lines)))
col_padding = ' ' * col_width
def format_line(line):
return '{col_padding} {line}'.format(col_padding=col_padding,
line=line)
header_lines = [
format_line(line) for line in json[:offset].splitlines()
]
formatted_json_lines = [
('{line_number:{col_width}}: {line}'.format(
col_width=col_width, line_number=line_number, line=line))
for line_number, line in enumerate(json_lines, start=1)
]
for line_number, line in comment_lines:
formatted_json_lines.insert(line_number, format_line(line))
raise ParseError('{error}\nIn document:\n{json_data}'.format(
error=e,
json_data='\n'.join(header_lines + formatted_json_lines)))
return objects
