class_docstr: Works exactly like the regular `SandboxedEnvironment` but does not
  permit modifications on the builtin mutable objects `list`, `set`, and
  `dict` by using the :func:`modifies_known_mutable` function.
code: def is_safe_attribute(self, obj, attr, value):
      if not SandboxedEnvironment.is_safe_attribute(
          self, obj, attr, value
      ):
          return False
      return not modifies_known_mutable(obj, attr)
  
imports: import operator
  import types
  import warnings
  from collections import deque
  from string import Formatter
  from markupsafe import EscapeFormatter
  from markupsafe import Markup
  from ._compat import abc
  from ._compat import PY2
  from ._compat import range_type
  from ._compat import string_types
  from .environment import Environment
  from .exceptions import SecurityError
label_desc: Use image node_id 1 for calling the ImmutableSandboxedEnvironment obj's underlying member method code with example usage: obj.is_safe_attribute(obj, attr, value) and returns: unknown, False