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pluckable - object lazy wrapper that supports chained soft get/slice of
items and/or attributes like::
pluckable(obj).users[2:5, 10:15].name.first
pluckable({"v": namedtuple("Vector", "x y z")(1, 2, 3)}).v.x
# pluckable([{'a': {2: 1}}]).a.2 --> 1
from __future__ import absolute_import
import sys
from .compat import xrange, baseinteger, basestring, unicode
class AttrSelector(unicode):
"""String key with preferrence for attribute plucking (`getattr`)."""
class KeySelector(unicode):
"""String key with preferrence for item plucking (`__getitem__`)."""
class pluckable(object):
def __init__(self, obj=None, default=None, skipmissing=True,
inplace=False, empty=False):
"""Creates a new pluckable object based on `obj`. Default value for the
missing keys is given with `default`.
A two modes of plucking are supported::
(1) the default, document databases alike, where missing keys (and it's
ancestors) will be silently dropped-out -- except for the leaf
nodes -- which always default to the ``default`` when missing.
(2) one-on-one extractor (explict mode), which will include all missing
values as ``default``, ensuring the leaf values exist even when one
(or more) intermediate nodes are missing.
self.obj = obj
self.default = default
self.skipmissing = skipmissing
self.inplace = inplace
self.empty = empty
def rewrap(self, **kwargs):
"""Inplace constructor. Depending on `self.inplace`, rewrap `obj`, or
just update internal vars, possibly including the `obj`.
if self.inplace:
for key, val in kwargs.items():
setattr(self, key, val)
return self
for key in ['obj', 'default', 'skipmissing', 'inplace', 'empty']:
kwargs.setdefault(key, getattr(self, key))
return pluckable(**kwargs)
def value(self):
if self.empty:
return self.default
return self.obj
def _append(self, obj, key, res, skipmissing=None):
if skipmissing is None:
skipmissing = self.skipmissing
# prefer attributes over items
if isinstance(key, AttrSelector):
res.append(getattr(obj, key))
except: # AttributeError et al
except: # KeyError et al
if not skipmissing:
return res
# by default, prefer itemgetter over attrgetter (key ~ KeySelector)
except: # KeyError et al
res.append(getattr(obj, key))
except: # AttributeError et al
if not skipmissing:
return res
def _filtered_list(self, selector):
"""Iterate over `self.obj` list, extracting `selector` from each
element. The `selector` can be a simple integer index, or any valid
key (hashable object).
res = []
for elem in self.obj:
self._append(elem, selector, res)
return res
def _sliced_list(self, selector):
"""For slice selectors operating on lists, we need to handle them
differently, depending on ``skipmissing``. In explicit mode, we may have
to expand the list with ``default`` values.
if self.skipmissing:
return self.obj[selector]
# TODO: can be optimized by observing list bounds
keys = xrange(selector.start or 0,
selector.stop or sys.maxint,
selector.step or 1)
res = []
for key in keys:
self._append(self.obj, key, res, skipmissing=False)
return res
def _extract_from_list(self, selector):
if isinstance(selector, baseinteger):
return self._sliced_list(slice(selector, selector+1))
elif isinstance(selector, slice):
return self._sliced_list(selector)
return self._filtered_list(selector)
def _extract_from_object(self, selector):
"""Extracts all values from `self.obj` object addressed with a `selector`.
Selector can be a ``slice``, or a singular value extractor in form of a
valid dictionary key (hashable object).
Object (operated on) can be anything with an itemgetter or attrgetter,
including, but limited to `dict`, and `list`.
Itemgetter is preferred over attrgetter, except when called as `.key`.
If `selector` is a singular value extractor (like a string, integer,
etc), a single value (for a given key) is returned if key exists, an
empty list if not.
If `selector` is a ``slice``, each key from that range is extracted;
failing-back, again, to an empty list.
if isinstance(selector, slice):
# we must expand the slice manually, in order to be able to apply to
# for example, to mapping types, or general objects
# (e.g. slice `4::2` will filter all even numerical keys/attrs >=4)
start = selector.start or 0
step = selector.step or 1
if selector.stop is None:
if hasattr(self.obj, "keys"):
# filter keys by slice
keys = \
[k for k in self.obj.keys() if isinstance(k, baseinteger) \
and k >= start and (k - start) % step == 0]
elif hasattr(self.obj, "__len__"):
# object we slice should have a length (__len__ method),
keys = xrange(start, len(self.obj), step)
# otherwise, we don't know how to slice, so just skip it,
# instead of failing
keys = []
keys = xrange(start, selector.stop, step)
keys = [selector]
res = []
for key in keys:
self._append(self.obj, key, res)
return res
def _get_all(self, *selectors):
res = []
for selector in selectors:
if isinstance(self.obj, list):
# Should we collapse the result list to a singular result?
# We should, if we filter by only one simple selector (index or key),
# except when we filter a list with the key selector.
# (cases: anything[idx], dict["key"]/obj.attr)
# We are doing this here, and not in selector extractors above, to make
# combining results from multiple selectors easier.
singular_result = False
if len(selectors) == 1:
is_idx = isinstance(selectors[0], baseinteger)
is_key = isinstance(selectors[0], basestring)
not_list = not isinstance(self.obj, list)
singular_result = is_idx or is_key and not_list
if len(res) == 0:
return self.rewrap(empty=True)
elif len(res) == 1 and singular_result:
return self.rewrap(obj=res[0])
return self.rewrap(obj=res)
def __getattr__(self, name):
"""Handle ```` lookups.
obj.key -> similar to obj["key"], but with preferrence on attributes vs items.
If obj is a dict, and "key" is not a valid `dict` attribute, extract
dict value under key "key" (or default val). If obj is a list,
iterate over all elements, extracting "key" from each element
return self._get_all(AttrSelector(name))
def __getitem__(self, key):
"""Handle various ``obj[key]`` lookups, including::
obj[2] -> if obj is list, extract elem with index 2;
if obj is dict, extract value under key 2
obj[1, 2] -> if obj is list, extract elems with indices 1 and 2;
if obj is dict, extract values under keys 1,2 into a new list
obj[1:5] -> the same as obj[1,2,3,4,5]
obj["key"] -> if obj is dict, extract value under key "key" (or default val),
if obj is list, iterate over all elements, extracting "key" from each element
obj[2, 4:5] -> the same as obj[2,4,5]
obj[1:, 0] -> analog to the above, sugar syntax for: obj[1:] + [obj[0]]
obj["x", "y"] -> if obj is dict, extract keys "x" and "y" into a new list;
if obj is list, iterate over all elements, extracting "x" and "y"
from each element into a flat list
obj["x", "y", 3, ::-1] -> similar to above, extracting "x", "y", 3 and all keys in reverse
# accept any iterable for indices
keys = iter(key)
except TypeError:
keys = (key,)
return self._get_all(*keys)
def __str__(self):
return str(self.value)
def __repr__(self):
return repr(self.value)
def __iter__(self):
"""Iterate over values plucked so far.
for val in pluckable(obj).users.last:
if self.empty:
return iter([])
val = self.value
return iter(val)
except Exception as e:
return iter([val])
def items(self):
"""Behave like `dict.items` for mapping types (iterator over (key, value)
pairs), and like `iter` for sequence types (iterator over values).
if self.empty:
return iter([])
val = self.value
if hasattr(val, "iteritems"):
return val.iteritems()
elif hasattr(val, "items"):
return val.items()
return iter(self)
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