PERF: allow a cache_readonly to be 'set' if allow_settings is passed on the decoration

 useful when specifiying an index that is **known** to be unique (e.g. in the case of a default range index)

Author: jreback

pandas/core/common.py

@@ -1156,6 +1156,7 @@ def _default_index(n):
  values = np.arange(n, dtype=np.int64)
  result = values.view(Int64Index)
  result.name = None
+ result.is_unique = True
  return result
 
 

pandas/core/index.py

@@ -278,7 +278,7 @@ def is_monotonic(self):
  def is_lexsorted_for_tuple(self, tup):
  return True
 
- @cache_readonly
+ @cache_readonly(allow_setting=True)
  def is_unique(self):
  return self._engine.is_unique
 

pandas/src/properties.pyx

@@ -4,16 +4,20 @@ from cpython cimport PyDict_Contains, PyDict_GetItem, PyDict_GetItem
 cdef class cache_readonly(object):
 
  cdef readonly:
- object fget, name
+ object func, name, allow_setting
 
- def __init__(self, func):
- self.fget = func
- self.name = func.__name__
+ def __init__(self, func=None, allow_setting=False):
+ if func is not None:
+ self.func = func
+ self.name = func.__name__
+ self.allow_setting = allow_setting
 
- def __get__(self, obj, type):
- if obj is None:
- return self.fget
+ def __call__(self, func, doc=None):
+ self.func = func
+ self.name = func.__name__
+ return self
 
+ def __get__(self, obj, typ):
  # Get the cache or set a default one if needed
 
  cache = getattr(obj, '_cache', None)
@@ -23,12 +27,23 @@ cdef class cache_readonly(object):
  if PyDict_Contains(cache, self.name):
  # not necessary to Py_INCREF
  val = <object> PyDict_GetItem(cache, self.name)
- return val
  else:
- val = self.fget(obj)
+ val = self.func(obj)
  PyDict_SetItem(cache, self.name, val)
- return val
+ return val
+
+ def __set__(self, obj, value):
+
+ if not self.allow_setting:
+ raise Exception("cannot set values for [%s]" % self.name)
+
+ # Get the cache or set a default one if needed
+ cache = getattr(obj, '_cache', None)
+ if cache is None:
+ cache = obj._cache = {}
 
+ PyDict_SetItem(cache, self.name, value)
+ 
 cdef class AxisProperty(object):
  cdef:
  Py_ssize_t axis