Current File : //usr/share/doc/python3-pycparser/examples/c_json.py
#------------------------------------------------------------------------------
# pycparser: c_json.py
#
# by Michael White (@mypalmike)
#
# This example includes functions to serialize and deserialize an ast
# to and from json format. Serializing involves walking the ast and converting
# each node from a python Node object into a python dict. Deserializing
# involves the opposite conversion, walking the tree formed by the
# dict and converting each dict into the specific Node object it represents.
# The dict itself is serialized and deserialized using the python json module.
#
# The dict representation is a fairly direct transformation of the object
# attributes. Each node in the dict gets one metadata field referring to the
# specific node class name, _nodetype. Each local attribute (i.e. not linking
# to child nodes) has a string value or array of string values. Each child
# attribute is either another dict or an array of dicts, exactly as in the
# Node object representation. The "coord" attribute, representing the
# node's location within the source code, is serialized/deserialized from
# a Coord object into a string of the format "filename:line[:column]".
#
# Example TypeDecl node, with IdentifierType child node, represented as a dict:
# "type": {
# "_nodetype": "TypeDecl",
# "coord": "c_files/funky.c:8",
# "declname": "o",
# "quals": [],
# "type": {
# "_nodetype": "IdentifierType",
# "coord": "c_files/funky.c:8",
# "names": [
# "char"
# ]
# }
# }
#------------------------------------------------------------------------------
from __future__ import print_function
import json
import sys
import re
from pycparser import parse_file, c_ast
from pycparser.plyparser import Coord
RE_CHILD_ARRAY = re.compile(r'(.*)\[(.*)\]')
RE_INTERNAL_ATTR = re.compile('__.*__')
class CJsonError(Exception):
pass
def memodict(fn):
""" Fast memoization decorator for a function taking a single argument """
class memodict(dict):
def __missing__(self, key):
ret = self[key] = fn(key)
return ret
return memodict().__getitem__
@memodict
def child_attrs_of(klass):
"""
Given a Node class, get a set of child attrs.
Memoized to avoid highly repetitive string manipulation
"""
non_child_attrs = set(klass.attr_names)
all_attrs = set([i for i in klass.__slots__ if not RE_INTERNAL_ATTR.match(i)])
return all_attrs - non_child_attrs
def to_dict(node):
""" Recursively convert an ast into dict representation. """
klass = node.__class__
result = {}
# Metadata
result['_nodetype'] = klass.__name__
# Local node attributes
for attr in klass.attr_names:
result[attr] = getattr(node, attr)
# Coord object
if node.coord:
result['coord'] = str(node.coord)
else:
result['coord'] = None
# Child attributes
for child_name, child in node.children():
# Child strings are either simple (e.g. 'value') or arrays (e.g. 'block_items[1]')
match = RE_CHILD_ARRAY.match(child_name)
if match:
array_name, array_index = match.groups()
array_index = int(array_index)
# arrays come in order, so we verify and append.
result[array_name] = result.get(array_name, [])
if array_index != len(result[array_name]):
raise CJsonError('Internal ast error. Array {} out of order. '
'Expected index {}, got {}'.format(
array_name, len(result[array_name]), array_index))
result[array_name].append(to_dict(child))
else:
result[child_name] = to_dict(child)
# Any child attributes that were missing need "None" values in the json.
for child_attr in child_attrs_of(klass):
if child_attr not in result:
result[child_attr] = None
return result
def to_json(node, **kwargs):
""" Convert ast node to json string """
return json.dumps(to_dict(node), **kwargs)
def file_to_dict(filename):
""" Load C file into dict representation of ast """
ast = parse_file(filename, use_cpp=True)
return to_dict(ast)
def file_to_json(filename, **kwargs):
""" Load C file into json string representation of ast """
ast = parse_file(filename, use_cpp=True)
return to_json(ast, **kwargs)
def _parse_coord(coord_str):
""" Parse coord string (file:line[:column]) into Coord object. """
if coord_str is None:
return None
vals = coord_str.split(':')
vals.extend([None] * 3)
filename, line, column = vals[:3]
return Coord(filename, line, column)
def _convert_to_obj(value):
"""
Convert an object in the dict representation into an object.
Note: Mutually recursive with from_dict.
"""
value_type = type(value)
if value_type == dict:
return from_dict(value)
elif value_type == list:
return [_convert_to_obj(item) for item in value]
else:
# String
return value
def from_dict(node_dict):
""" Recursively build an ast from dict representation """
class_name = node_dict.pop('_nodetype')
klass = getattr(c_ast, class_name)
# Create a new dict containing the key-value pairs which we can pass
# to node constructors.
objs = {}
for key, value in node_dict.items():
if key == 'coord':
objs[key] = _parse_coord(value)
else:
objs[key] = _convert_to_obj(value)
# Use keyword parameters, which works thanks to beautifully consistent
# ast Node initializers.
return klass(**objs)
def from_json(ast_json):
""" Build an ast from json string representation """
return from_dict(json.loads(ast_json))
#------------------------------------------------------------------------------
if __name__ == "__main__":
if len(sys.argv) > 1:
# Some test code...
# Do trip from C -> ast -> dict -> ast -> json, then print.
ast_dict = file_to_dict(sys.argv[1])
ast = from_dict(ast_dict)
print(to_json(ast, sort_keys=True, indent=4))
else:
print("Please provide a filename as argument")
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