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_get_attr_raise_on_attribute_error = "RAISE ON EXCEPTION"
def get_attr(obj, string_rep, default=_get_attr_raise_on_attribute_error, separator="."):
""" getattr via a chain of attributes like so:
>>> import datetime
>>> some_date = datetime.date.today()
>>> get_attr(some_date, "month.numerator.__doc__")
'int(x[, base]) -> integer\n\nConvert a string or number to an integer, ...
"""
attribute_chain = string_rep.split(separator)
current_obj = obj
for attr in attribute_chain:
try:
current_obj = getattr(current_obj, attr)
except AttributeError:
if default is _get_attr_raise_on_attribute_error:
raise AttributeError(
"Bad attribute \"{}\" in chain: \"{}\"".format(attr, string_rep)
)
return default
return current_obj
class ImmutableWrapper(object):
_obj = None
_recursive = None
def __init__(self, obj, recursive):
self._obj = obj
self._recursive = recursive
def __setattr__(self, name, val):
if name == "_obj" and self._obj is None:
object.__setattr__(self, name, val)
return
elif name == "_recursive" and self._recursive is None:
object.__setattr__(self, name, val)
return
raise AttributeError("This object has been marked as immutable; you cannot set its attributes.")
def __getattr__(self, name):
if self._recursive:
return immutable(getattr(self._obj, name), recursive=self._recursive)
return getattr(self._obj, name)
def __repr__(self):
return "<Immutable {}: {}>".format(self._obj.__class__.__name__, self._obj.__repr__())
def immutable(obj, recursive=True):
"""wraps the argument in a pass-through class that disallows all attribute
setting. If the `recursive` flag is true, all attribute accesses will
return an immutable-wrapped version of the "real" attribute."""
return ImmutableWrapper(obj, recursive)
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