bpython/bpython/simpleeval.py at inheritance-over-composition · optionalg/bpython · GitHub

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# encoding: utf-8

# The MIT License

# 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 attribute lookup currently occuring on"""

# 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))

bpython/bpython/simpleeval.py at inheritance-over-composition · optionalg/bpython · GitHub

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