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# encoding: utf-8
# The MIT License
#
# Copyright (c) 2015 the bpython authors.
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.
#
"""simple evaluation of side-effect free code
In order to provide fancy completion, some code can be executed safely.
"""
import ast
from six import string_types
from six.moves import builtins
from bpython import line as line_properties
from bpython._py3compat import py3
_string_type_nodes = (ast.Str, ast.Bytes) if py3 else (ast.Str,)
_numeric_types = (int, float, complex) + (() if py3 else (long,))
# added in Python 3.4
if hasattr(ast, 'NameConstant'):
_name_type_nodes = (ast.Name, ast.NameConstant)
else:
_name_type_nodes = (ast.Name,)
class EvaluationError(Exception):
"""Raised if an exception occurred in safe_eval."""
def safe_eval(expr, namespace):
"""Not all that safe, just catches some errors"""
try:
return eval(expr, namespace)
except (NameError, AttributeError, SyntaxError):
# If debugging safe_eval, raise this!
# raise
raise EvaluationError
# This function is under the Python License, Version 2
# This license requires modifications to the code be reported.
# Based on ast.literal_eval in Python 2 and Python 3
# Modifications:
# * Python 2 and Python 3 versions of the function are combined
# * checks that objects used as operands of + and - are numbers
# instead of checking they are constructed with number literals
# * new docstring describing different functionality
# * looks up names from namespace
# * indexing syntax is allowed
def simple_eval(node_or_string, namespace=None):
"""
Safely evaluate an expression node or a string containing a Python
expression. The string or node provided may only consist of:
* the following Python literal structures: strings, numbers, tuples,
lists, and dicts
* variable names causing lookups in the passed in namespace or builtins
* getitem calls using the [] syntax on objects of the types above
Like the Python 3 (and unlike the Python 2) literal_eval, unary and binary
+ and - operations are allowed on all builtin numeric types.
The optional namespace dict-like ought not to cause side effects on lookup
"""
if namespace is None:
namespace = {}
if isinstance(node_or_string, string_types):
node_or_string = ast.parse(node_or_string, mode='eval')
if isinstance(node_or_string, ast.Expression):
node_or_string = node_or_string.body
def _convert(node):
if isinstance(node, _string_type_nodes):
return node.s
elif isinstance(node, ast.Num):
return node.n
elif isinstance(node, ast.Tuple):
return tuple(map(_convert, node.elts))
elif isinstance(node, ast.List):
return list(map(_convert, node.elts))
elif isinstance(node, ast.Dict):
return dict((_convert(k), _convert(v)) for k, v
in zip(node.keys, node.values))
# this is a deviation from literal_eval: we allow non-literals
elif isinstance(node, _name_type_nodes):
try:
return namespace[node.id]
except KeyError:
try:
return getattr(builtins, node.id)
except AttributeError:
raise EvaluationError("can't lookup %s" % node.id)
# unary + and - are allowed on any type
elif (isinstance(node, ast.UnaryOp) and
isinstance(node.op, (ast.UAdd, ast.USub))):
# ast.literal_eval does ast typechecks here, we use type checks
operand = _convert(node.operand)
if not type(operand) in _numeric_types:
raise ValueError("unary + and - only allowed on builtin nums")
if isinstance(node.op, ast.UAdd):
return + operand
else:
return - operand
elif (isinstance(node, ast.BinOp) and
isinstance(node.op, (ast.Add, ast.Sub))):
# ast.literal_eval does ast typechecks here, we use type checks
left = _convert(node.left)
right = _convert(node.right)
if not (type(left) in _numeric_types and
type(right) in _numeric_types):
raise ValueError("binary + and - only allowed on builtin nums")
if isinstance(node.op, ast.Add):
return left + right
else:
return left - right
# this is a deviation from literal_eval: we allow indexing
elif (isinstance(node, ast.Subscript) and
isinstance(node.slice, ast.Index)):
obj = _convert(node.value)
index = _convert(node.slice.value)
return safe_getitem(obj, index)
raise ValueError('malformed string')
return _convert(node_or_string)
def safe_getitem(obj, index):
if type(obj) in (list, tuple, dict, bytes) + string_types:
try:
return obj[index]
except (KeyError, IndexError):
raise EvaluationError("can't lookup key %r on %r" % (index, obj))
raise ValueError('unsafe to lookup on object of type %s' % (type(obj), ))
def find_attribute_with_name(node, name):
if isinstance(node, ast.Attribute) and node.attr == name:
return node
for item in ast.iter_child_nodes(node):
r = find_attribute_with_name(item, name)
if r:
return r
def evaluate_current_expression(cursor_offset, line, namespace=None):
"""
Return evaluated expression to the right of the dot of current attribute.
Only evaluates builtin objects, and do any attribute lookup.
"""
# Builds asts from with increasing numbers of characters back from cursor.
# Find the biggest valid ast.
# Once our attribute access is found, return its .value subtree
if namespace is None:
namespace = {}
# in case attribute is blank, e.g. foo.| -> foo.xxx|
temp_line = line[:cursor_offset] + 'xxx' + line[cursor_offset:]
temp_cursor = cursor_offset + 3
temp_attribute = line_properties.current_expression_attribute(
temp_cursor, temp_line)
if temp_attribute is None:
raise EvaluationError("No current attribute")
attr_before_cursor = temp_line[temp_attribute.start:temp_cursor]
def parse_trees(cursor_offset, line):
for i in range(cursor_offset - 1, -1, -1):
try:
tree = ast.parse(line[i:cursor_offset])
yield tree
except SyntaxError:
continue
largest_ast = None
for tree in parse_trees(temp_cursor, temp_line):
attribute_access = find_attribute_with_name(tree, attr_before_cursor)
if attribute_access:
largest_ast = attribute_access.value
if largest_ast is None:
raise EvaluationError(
"Corresponding ASTs to right of cursor are invalid")
try:
return simple_eval(largest_ast, namespace)
except ValueError:
raise EvaluationError("Could not safely evaluate")
def evaluate_current_attribute(cursor_offset, line, namespace=None):
"""Safely evaluates the expression having an attributed accesssed"""
# this function runs user code in case of custom descriptors,
# so could fail in any way
obj = evaluate_current_expression(cursor_offset, line, namespace)
attr = line_properties.current_expression_attribute(cursor_offset, line)
if attr is None:
raise EvaluationError("No attribute found to look up")
try:
return getattr(obj, attr.word)
except AttributeError:
raise EvaluationError(
"can't lookup attribute %s on %r" % (attr.word, obj))