Source code for boltons.iterutils

# -*- coding: utf-8 -*-
""":mod:`itertools` is full of great examples of Python generator
usage. However, there are still some critical gaps. ``iterutils``
fills many of those gaps with featureful, tested, and Pythonic

Many of the functions below have two versions, one which
returns an iterator (denoted by the ``*_iter`` naming pattern), and a
shorter-named convenience form that returns a list. Some of the
following are based on examples in itertools docs.

import os
import math
import time
import codecs
import random
import socket
import hashlib
import itertools

from collections import Mapping, Sequence, Set, ItemsView

    from typeutils import make_sentinel
    _UNSET = make_sentinel('_UNSET')
    _REMAP_EXIT = make_sentinel('_REMAP_EXIT')
except ImportError:
    _REMAP_EXIT = object()
    _UNSET = object()

    from future_builtins import filter
    from itertools import izip
    _IS_PY3 = False
except ImportError:
    # Python 3 compat
    _IS_PY3 = True
    basestring = (str, bytes)
    izip, xrange = zip, range

[docs]def is_iterable(obj): """Similar in nature to :func:`callable`, ``is_iterable`` returns ``True`` if an object is `iterable`_, ``False`` if not. >>> is_iterable([]) True >>> is_iterable(object()) False .. _iterable: """ try: iter(obj) except TypeError: return False return True
[docs]def is_scalar(obj): """A near-mirror of :func:`is_iterable`. Returns ``False`` if an object is an iterable container type. Strings are considered scalar as well, because strings are more often treated as whole values as opposed to iterables of 1-character substrings. >>> is_scalar(object()) True >>> is_scalar(range(10)) False >>> is_scalar('hello') True """ return not is_iterable(obj) or isinstance(obj, basestring)
[docs]def is_collection(obj): """The opposite of :func:`is_scalar`. Returns ``True`` if an object is an iterable other than a string. >>> is_collection(object()) False >>> is_collection(range(10)) True >>> is_collection('hello') False """ return is_iterable(obj) and not isinstance(obj, basestring)
[docs]def split(src, sep=None, maxsplit=None): """Splits an iterable based on a separator. Like :meth:`str.split`, but for all iterables. Returns a list of lists. >>> split(['hi', 'hello', None, None, 'sup', None, 'soap', None]) [['hi', 'hello'], ['sup'], ['soap']] See :func:`split_iter` docs for more info. """ return list(split_iter(src, sep, maxsplit))
[docs]def split_iter(src, sep=None, maxsplit=None): """Splits an iterable based on a separator, *sep*, a max of *maxsplit* times (no max by default). *sep* can be: * a single value * an iterable of separators * a single-argument callable that returns True when a separator is encountered ``split_iter()`` yields lists of non-separator values. A separator will never appear in the output. >>> list(split_iter(['hi', 'hello', None, None, 'sup', None, 'soap', None])) [['hi', 'hello'], ['sup'], ['soap']] Note that ``split_iter`` is based on :func:`str.split`, so if *sep* is ``None``, ``split()`` **groups** separators. If empty lists are desired between two contiguous ``None`` values, simply use ``sep=[None]``: >>> list(split_iter(['hi', 'hello', None, None, 'sup', None])) [['hi', 'hello'], ['sup']] >>> list(split_iter(['hi', 'hello', None, None, 'sup', None], sep=[None])) [['hi', 'hello'], [], ['sup'], []] Using a callable separator: >>> falsy_sep = lambda x: not x >>> list(split_iter(['hi', 'hello', None, '', 'sup', False], falsy_sep)) [['hi', 'hello'], [], ['sup'], []] See :func:`split` for a list-returning version. """ if not is_iterable(src): raise TypeError('expected an iterable') if maxsplit is not None: maxsplit = int(maxsplit) if maxsplit == 0: yield [src] return if callable(sep): sep_func = sep elif not is_scalar(sep): sep = frozenset(sep) sep_func = lambda x: x in sep else: sep_func = lambda x: x == sep cur_group = [] split_count = 0 for s in src: if maxsplit is not None and split_count >= maxsplit: sep_func = lambda x: False if sep_func(s): if sep is None and not cur_group: # If sep is none, str.split() "groups" separators # check the str.split() docs for more info continue split_count += 1 yield cur_group cur_group = [] else: cur_group.append(s) if cur_group or sep is not None: yield cur_group return
[docs]def chunked(src, size, count=None, **kw): """Returns a list of *count* chunks, each with *size* elements, generated from iterable *src*. If *src* is not evenly divisible by *size*, the final chunk will have fewer than *size* elements. Provide the *fill* keyword argument to provide a pad value and enable padding, otherwise no padding will take place. >>> chunked(range(10), 3) [[0, 1, 2], [3, 4, 5], [6, 7, 8], [9]] >>> chunked(range(10), 3, fill=None) [[0, 1, 2], [3, 4, 5], [6, 7, 8], [9, None, None]] >>> chunked(range(10), 3, count=2) [[0, 1, 2], [3, 4, 5]] See :func:`chunked_iter` for more info. """ chunk_iter = chunked_iter(src, size, **kw) if count is None: return list(chunk_iter) else: return list(itertools.islice(chunk_iter, count))
[docs]def chunked_iter(src, size, **kw): """Generates *size*-sized chunks from *src* iterable. Unless the optional *fill* keyword argument is provided, iterables not even divisible by *size* will have a final chunk that is smaller than *size*. >>> list(chunked_iter(range(10), 3)) [[0, 1, 2], [3, 4, 5], [6, 7, 8], [9]] >>> list(chunked_iter(range(10), 3, fill=None)) [[0, 1, 2], [3, 4, 5], [6, 7, 8], [9, None, None]] Note that ``fill=None`` in fact uses ``None`` as the fill value. """ # TODO: add count kwarg? if not is_iterable(src): raise TypeError('expected an iterable') size = int(size) if size <= 0: raise ValueError('expected a positive integer chunk size') do_fill = True try: fill_val = kw.pop('fill') except KeyError: do_fill = False fill_val = None if kw: raise ValueError('got unexpected keyword arguments: %r' % kw.keys()) if not src: return postprocess = lambda chk: chk if isinstance(src, basestring): postprocess = lambda chk, _sep=type(src)(): _sep.join(chk) src_iter = iter(src) while True: cur_chunk = list(itertools.islice(src_iter, size)) if not cur_chunk: break lc = len(cur_chunk) if lc < size and do_fill: cur_chunk[lc:] = [fill_val] * (size - lc) yield postprocess(cur_chunk) return
[docs]def pairwise(src): """Convenience function for calling :func:`windowed` on *src*, with *size* set to 2. >>> pairwise(range(5)) [(0, 1), (1, 2), (2, 3), (3, 4)] >>> pairwise([]) [] The number of pairs is always one less than the number of elements in the iterable passed in, except on empty inputs, which returns an empty list. """ return windowed(src, 2)
[docs]def pairwise_iter(src): """Convenience function for calling :func:`windowed_iter` on *src*, with *size* set to 2. >>> list(pairwise_iter(range(5))) [(0, 1), (1, 2), (2, 3), (3, 4)] >>> list(pairwise_iter([])) [] The number of pairs is always one less than the number of elements in the iterable passed in, or zero, when *src* is empty. """ return windowed_iter(src, 2)
[docs]def windowed(src, size): """Returns tuples with exactly length *size*. If the iterable is too short to make a window of length *size*, no tuples are returned. See :func:`windowed_iter` for more. """ return list(windowed_iter(src, size))
[docs]def windowed_iter(src, size): """Returns tuples with length *size* which represent a sliding window over iterable *src*. >>> list(windowed_iter(range(7), 3)) [(0, 1, 2), (1, 2, 3), (2, 3, 4), (3, 4, 5), (4, 5, 6)] If the iterable is too short to make a window of length *size*, then no window tuples are returned. >>> list(windowed_iter(range(3), 5)) [] """ # TODO: lists? (for consistency) tees = itertools.tee(src, size) try: for i, t in enumerate(tees): for _ in xrange(i): next(t) except StopIteration: return izip([]) return izip(*tees)
[docs]def xfrange(stop, start=None, step=1.0): """Same as :func:`frange`, but generator-based instead of returning a list. >>> tuple(xfrange(1, 3, step=0.75)) (1.0, 1.75, 2.5) See :func:`frange` for more details. """ if not step: raise ValueError('step must be non-zero') if start is None: start, stop = 0.0, stop * 1.0 else: # swap when all args are used stop, start = start * 1.0, stop * 1.0 cur = start while cur < stop: yield cur cur += step
[docs]def frange(stop, start=None, step=1.0): """A :func:`range` clone for float-based ranges. >>> frange(5) [0.0, 1.0, 2.0, 3.0, 4.0] >>> frange(6, step=1.25) [0.0, 1.25, 2.5, 3.75, 5.0] >>> frange(100.5, 101.5, 0.25) [100.5, 100.75, 101.0, 101.25] >>> frange(5, 0) [] >>> frange(5, 0, step=-1.25) [5.0, 3.75, 2.5, 1.25] """ if not step: raise ValueError('step must be non-zero') if start is None: start, stop = 0.0, stop * 1.0 else: # swap when all args are used stop, start = start * 1.0, stop * 1.0 count = int(math.ceil((stop - start) / step)) ret = [None] * count if not ret: return ret ret[0] = start for i in xrange(1, count): ret[i] = ret[i - 1] + step return ret
[docs]def backoff(start, stop, count=None, factor=2.0, jitter=False): """Returns a list of geometrically-increasing floating-point numbers, suitable for usage with `exponential backoff`_. Exactly like :func:`backoff_iter`, but without the ``'repeat'`` option for *count*. See :func:`backoff_iter` for more details. .. _exponential backoff: >>> backoff(1, 10) [1.0, 2.0, 4.0, 8.0, 10.0] """ if count == 'repeat': raise ValueError("'repeat' supported in backoff_iter, not backoff") return list(backoff_iter(start, stop, count=count, factor=factor, jitter=jitter))
[docs]def backoff_iter(start, stop, count=None, factor=2.0, jitter=False): """Generates a sequence of geometrically-increasing floats, suitable for usage with `exponential backoff`_. Starts with *start*, increasing by *factor* until *stop* is reached, optionally stopping iteration once *count* numbers are yielded. *factor* defaults to 2. In general retrying with properly-configured backoff creates a better-behaved component for a larger service ecosystem. .. _exponential backoff: >>> list(backoff_iter(1.0, 10.0, count=5)) [1.0, 2.0, 4.0, 8.0, 10.0] >>> list(backoff_iter(1.0, 10.0, count=8)) [1.0, 2.0, 4.0, 8.0, 10.0, 10.0, 10.0, 10.0] >>> list(backoff_iter(0.25, 100.0, factor=10)) [0.25, 2.5, 25.0, 100.0] A simplified usage example: .. code-block:: python for timeout in backoff_iter(0.25, 5.0): try: res = network_call() break except Exception as e: log(e) time.sleep(timeout) An enhancement for large-scale systems would be to add variation, or *jitter*, to timeout values. This is done to avoid a thundering herd on the receiving end of the network call. Finally, for *count*, the special value ``'repeat'`` can be passed to continue yielding indefinitely. Args: start (float): Positive number for baseline. stop (float): Positive number for maximum. count (int): Number of steps before stopping iteration. Defaults to the number of steps between *start* and *stop*. Pass the string, `'repeat'`, to continue iteration indefinitely. factor (float): Rate of exponential increase. Defaults to `2.0`, e.g., `[1, 2, 4, 8, 16]`. jitter (float): A factor between `-1.0` and `1.0`, used to uniformly randomize and thus spread out timeouts in a distributed system, avoiding rhythm effects. Positive values use the base backoff curve as a maximum, negative values use the curve as a minimum. Set to 1.0 or `True` for a jitter approximating Ethernet's time-tested backoff solution. Defaults to `False`. """ start = float(start) stop = float(stop) factor = float(factor) if start < 0.0: raise ValueError('expected start >= 0, not %r' % start) if factor < 1.0: raise ValueError('expected factor >= 1.0, not %r' % factor) if stop == 0.0: raise ValueError('expected stop >= 0') if stop < start: raise ValueError('expected stop >= start, not %r' % stop) if count is None: denom = start if start else 1 count = 1 + math.ceil(math.log(stop/denom, factor)) count = count if start else count + 1 if count != 'repeat' and count < 0: raise ValueError('count must be positive or "repeat", not %r' % count) if jitter: jitter = float(jitter) if not (-1.0 <= jitter <= 1.0): raise ValueError('expected jitter -1 <= j <= 1, not: %r' % jitter) cur, i = start, 0 while count == 'repeat' or i < count: if not jitter: cur_ret = cur elif jitter: cur_ret = cur - (cur * jitter * random.random()) yield cur_ret i += 1 if cur == 0: cur = 1 elif cur < stop: cur *= factor if cur > stop: cur = stop return
[docs]def bucketize(src, key=None, value_transform=None, key_filter=None): """Group values in the *src* iterable by the value returned by *key*, which defaults to :class:`bool`, grouping values by truthiness. >>> bucketize(range(5)) {False: [0], True: [1, 2, 3, 4]} >>> is_odd = lambda x: x % 2 == 1 >>> bucketize(range(5), is_odd) {False: [0, 2, 4], True: [1, 3]} Value lists are not deduplicated: >>> bucketize([None, None, None, 'hello']) {False: [None, None, None], True: ['hello']} Bucketize into more than 3 groups >>> bucketize(range(10), lambda x: x % 3) {0: [0, 3, 6, 9], 1: [1, 4, 7], 2: [2, 5, 8]} ``bucketize`` has a couple of advanced options useful in certain cases. *value_transform* can be used to modify values as they are added to buckets, and *key_filter* will allow excluding certain buckets from being collected. >>> bucketize(range(5), value_transform=lambda x: x*x) {False: [0], True: [1, 4, 9, 16]} >>> bucketize(range(10), key=lambda x: x % 3, key_filter=lambda k: k % 3 != 1) {0: [0, 3, 6, 9], 2: [2, 5, 8]} Note in some of these examples there were at most two keys, ``True`` and ``False``, and each key present has a list with at least one item. See :func:`partition` for a version specialized for binary use cases. """ if not is_iterable(src): raise TypeError('expected an iterable') if key is None: key = bool if not callable(key): raise TypeError('expected callable key function') if value_transform is None: value_transform = lambda x: x if not callable(value_transform): raise TypeError('expected callable value transform function') ret = {} for val in src: key_of_val = key(val) if key_filter is None or key_filter(key_of_val): ret.setdefault(key_of_val, []).append(value_transform(val)) return ret
[docs]def partition(src, key=None): """No relation to :meth:`str.partition`, ``partition`` is like :func:`bucketize`, but for added convenience returns a tuple of ``(truthy_values, falsy_values)``. >>> nonempty, empty = partition(['', '', 'hi', '', 'bye']) >>> nonempty ['hi', 'bye'] *key* defaults to :class:`bool`, but can be carefully overridden to use any function that returns either ``True`` or ``False``. >>> import string >>> is_digit = lambda x: x in string.digits >>> decimal_digits, hexletters = partition(string.hexdigits, is_digit) >>> ''.join(decimal_digits), ''.join(hexletters) ('0123456789', 'abcdefABCDEF') """ bucketized = bucketize(src, key) return bucketized.get(True, []), bucketized.get(False, [])
[docs]def unique(src, key=None): """``unique()`` returns a list of unique values, as determined by *key*, in the order they first appeared in the input iterable, *src*. >>> ones_n_zeros = '11010110001010010101010' >>> ''.join(unique(ones_n_zeros)) '10' See :func:`unique_iter` docs for more details. """ return list(unique_iter(src, key))
[docs]def unique_iter(src, key=None): """Yield unique elements from the iterable, *src*, based on *key*, in the order in which they first appeared in *src*. >>> repetitious = [1, 2, 3] * 10 >>> list(unique_iter(repetitious)) [1, 2, 3] By default, *key* is the object itself, but *key* can either be a callable or, for convenience, a string name of the attribute on which to uniqueify objects, falling back on identity when the attribute is not present. >>> pleasantries = ['hi', 'hello', 'ok', 'bye', 'yes'] >>> list(unique_iter(pleasantries, key=lambda x: len(x))) ['hi', 'hello', 'bye'] """ if not is_iterable(src): raise TypeError('expected an iterable, not %r' % type(src)) if key is None: key_func = lambda x: x elif callable(key): key_func = key elif isinstance(key, basestring): key_func = lambda x: getattr(x, key, x) else: raise TypeError('"key" expected a string or callable, not %r' % key) seen = set() for i in src: k = key_func(i) if k not in seen: seen.add(k) yield i return
[docs]def one(src, default=None, key=None): """Along the same lines as builtins, :func:`all` and :func:`any`, and similar to :func:`first`, ``one()`` returns the single object in the given iterable *src* that evaluates to ``True``, as determined by callable *key*. If unset, *key* defaults to :class:`bool`. If no such objects are found, *default* is returned. If *default* is not passed, ``None`` is returned. If *src* has more than one object that evaluates to ``True``, or if there is no object that fulfills such condition, return *default*. It's like an `XOR`_ over an iterable. >>> one((True, False, False)) True >>> one((True, False, True)) >>> one((0, 0, 'a')) 'a' >>> one((0, False, None)) >>> one((True, True), default=False) False >>> bool(one(('', 1))) True >>> one((10, 20, 30, 42), key=lambda i: i > 40) 42 See `Martín Gaitán's original repo`_ for further use cases. .. _Martín Gaitán's original repo: .. _XOR: """ ones = list(itertools.islice(filter(key, src), 2)) return ones[0] if len(ones) == 1 else default
[docs]def first(iterable, default=None, key=None): """Return first element of *iterable* that evaluates to ``True``, else return ``None`` or optional *default*. Similar to :func:`one`. >>> first([0, False, None, [], (), 42]) 42 >>> first([0, False, None, [], ()]) is None True >>> first([0, False, None, [], ()], default='ohai') 'ohai' >>> import re >>> m = first(re.match(regex, 'abc') for regex in ['b.*', 'a(.*)']) >>> 'bc' The optional *key* argument specifies a one-argument predicate function like that used for *filter()*. The *key* argument, if supplied, should be in keyword form. For example, finding the first even number in an iterable: >>> first([1, 1, 3, 4, 5], key=lambda x: x % 2 == 0) 4 Contributed by Hynek Schlawack, author of `the original standalone module`_. .. _the original standalone module: """ return next(filter(key, iterable), default)
[docs]def same(iterable, ref=_UNSET): """``same()`` returns ``True`` when all values in *iterable* are equal to one another, or optionally a reference value, *ref*. Similar to :func:`all` and :func:`any` in that it evaluates an iterable and returns a :class:`bool`. ``same()`` returns ``True`` for empty iterables. >>> same([]) True >>> same([1]) True >>> same(['a', 'a', 'a']) True >>> same(range(20)) False >>> same([[], []]) True >>> same([[], []], ref='test') False """ iterator = iter(iterable) if ref is _UNSET: ref = next(iterator, ref) return all(val == ref for val in iterator)
def default_visit(path, key, value): # print('visit(%r, %r, %r)' % (path, key, value)) return key, value # enable the extreme: monkeypatching iterutils with a different default_visit _orig_default_visit = default_visit def default_enter(path, key, value): # print('enter(%r, %r)' % (key, value)) if isinstance(value, basestring): return value, False elif isinstance(value, Mapping): return value.__class__(), ItemsView(value) elif isinstance(value, Sequence): return value.__class__(), enumerate(value) elif isinstance(value, Set): return value.__class__(), enumerate(value) else: # files, strings, other iterables, and scalars are not # traversed return value, False def default_exit(path, key, old_parent, new_parent, new_items): # print('exit(%r, %r, %r, %r, %r)' # % (path, key, old_parent, new_parent, new_items)) ret = new_parent if isinstance(new_parent, Mapping): new_parent.update(new_items) elif isinstance(new_parent, Sequence): vals = [v for i, v in new_items] try: new_parent.extend(vals) except AttributeError: ret = new_parent.__class__(vals) # tuples elif isinstance(new_parent, Set): vals = [v for i, v in new_items] try: new_parent.update(vals) except AttributeError: ret = new_parent.__class__(vals) # frozensets else: raise RuntimeError('unexpected iterable type: %r' % type(new_parent)) return ret
[docs]def remap(root, visit=default_visit, enter=default_enter, exit=default_exit, **kwargs): """The remap ("recursive map") function is used to traverse and transform nested structures. Lists, tuples, sets, and dictionaries are just a few of the data structures nested into heterogenous tree-like structures that are so common in programming. Unfortunately, Python's built-in ways to manipulate collections are almost all flat. List comprehensions may be fast and succinct, but they do not recurse, making it tedious to apply quick changes or complex transforms to real-world data. remap goes where list comprehensions cannot. Here's an example of removing all Nones from some data: >>> from pprint import pprint >>> reviews = {'Star Trek': {'TNG': 10, 'DS9': 8.5, 'ENT': None}, ... 'Babylon 5': 6, 'Dr. Who': None} >>> pprint(remap(reviews, lambda p, k, v: v is not None)) {'Babylon 5': 6, 'Star Trek': {'DS9': 8.5, 'TNG': 10}} Notice how both Nones have been removed despite the nesting in the dictionary. Not bad for a one-liner, and that's just the beginning. See `this remap cookbook`_ for more delicious recipes. .. _this remap cookbook: remap takes four main arguments: the object to traverse and three optional callables which determine how the remapped object will be created. Args: root: The target object to traverse. By default, remap supports iterables like :class:`list`, :class:`tuple`, :class:`dict`, and :class:`set`, but any object traversable by *enter* will work. visit (callable): This function is called on every item in *root*. It must accept three positional arguments, *path*, *key*, and *value*. *path* is simply a tuple of parents' keys. *visit* should return the new key-value pair. It may also return ``True`` as shorthand to keep the old item unmodified, or ``False`` to drop the item from the new structure. *visit* is called after *enter*, on the new parent. The *visit* function is called for every item in root, including duplicate items. For traversable values, it is called on the new parent object, after all its children have been visited. The default visit behavior simply returns the key-value pair unmodified. enter (callable): This function controls which items in *root* are traversed. It accepts the same arguments as *visit*: the path, the key, and the value of the current item. It returns a pair of the blank new parent, and an iterator over the items which should be visited. If ``False`` is returned instead of an iterator, the value will not be traversed. The *enter* function is only called once per unique value. The default enter behavior support mappings, sequences, and sets. Strings and all other iterables will not be traversed. exit (callable): This function determines how to handle items once they have been visited. It gets the same three arguments as the other functions -- *path*, *key*, *value* -- plus two more: the blank new parent object returned from *enter*, and a list of the new items, as remapped by *visit*. Like *enter*, the *exit* function is only called once per unique value. The default exit behavior is to simply add all new items to the new parent, e.g., using :meth:`list.extend` and :meth:`dict.update` to add to the new parent. Immutable objects, such as a :class:`tuple` or :class:`namedtuple`, must be recreated from scratch, but use the same type as the new parent passed back from the *enter* function. reraise_visit (bool): A pragmatic convenience for the *visit* callable. When set to ``False``, remap ignores any errors raised by the *visit* callback. Items causing exceptions are kept. See examples for more details. remap is designed to cover the majority of cases with just the *visit* callable. While passing in multiple callables is very empowering, remap is designed so very few cases should require passing more than one function. When passing *enter* and *exit*, it's common and easiest to build on the default behavior. Simply add ``from boltons.iterutils import default_enter`` (or ``default_exit``), and have your enter/exit function call the default behavior before or after your custom logic. See `this example`_. Duplicate and self-referential objects (aka reference loops) are automatically handled internally, `as shown here`_. .. _this example: .. _as shown here: """ # TODO: improve argument formatting in sphinx doc # TODO: enter() return (False, items) to continue traverse but cancel copy? if not callable(visit): raise TypeError('visit expected callable, not: %r' % visit) if not callable(enter): raise TypeError('enter expected callable, not: %r' % enter) if not callable(exit): raise TypeError('exit expected callable, not: %r' % exit) reraise_visit = kwargs.pop('reraise_visit', True) if kwargs: raise TypeError('unexpected keyword arguments: %r' % kwargs.keys()) path, registry, stack = (), {}, [(None, root)] new_items_stack = [] while stack: key, value = stack.pop() id_value = id(value) if key is _REMAP_EXIT: key, new_parent, old_parent = value id_value = id(old_parent) path, new_items = new_items_stack.pop() value = exit(path, key, old_parent, new_parent, new_items) registry[id_value] = value if not new_items_stack: continue elif id_value in registry: value = registry[id_value] else: res = enter(path, key, value) try: new_parent, new_items = res except TypeError: # TODO: handle False? raise TypeError('enter should return a tuple of (new_parent,' ' items_iterator), not: %r' % res) if new_items is not False: # traverse unless False is explicitly passed registry[id_value] = new_parent new_items_stack.append((path, [])) if value is not root: path += (key,) stack.append((_REMAP_EXIT, (key, new_parent, value))) if new_items: stack.extend(reversed(list(new_items))) continue if visit is _orig_default_visit: # avoid function call overhead by inlining identity operation visited_item = (key, value) else: try: visited_item = visit(path, key, value) except Exception: if reraise_visit: raise visited_item = True if visited_item is False: continue # drop elif visited_item is True: visited_item = (key, value) # TODO: typecheck? # raise TypeError('expected (key, value) from visit(),' # ' not: %r' % visited_item) try: new_items_stack[-1][1].append(visited_item) except IndexError: raise TypeError('expected remappable root, not: %r' % root) return value
class PathAccessError(KeyError, IndexError, TypeError): """An amalgamation of KeyError, IndexError, and TypeError, representing what can occur when looking up a path in a nested object. """ def __init__(self, exc, seg, path): self.exc = exc self.seg = seg self.path = path def __repr__(self): cn = self.__class__.__name__ return '%s(%r, %r, %r)' % (cn, self.exc, self.seg, self.path) def __str__(self): return ('could not access %r from path %r, got error: %r' % (self.seg, self.path, self.exc))
[docs]def get_path(root, path, default=_UNSET): """Retrieve a value from a nested object via a tuple representing the lookup path. >>> root = {'a': {'b': {'c': [[1], [2], [3]]}}} >>> get_path(root, ('a', 'b', 'c', 2, 0)) 3 The path format is intentionally consistent with that of :func:`remap`. One of get_path's chief aims is improved error messaging. EAFP is great, but the error messages are not. For instance, ``root['a']['b']['c'][2][1]`` gives back ``IndexError: list index out of range`` What went out of range where? get_path currently raises ``PathAccessError: could not access 2 from path ('a', 'b', 'c', 2, 1), got error: IndexError('list index out of range',)``, a subclass of IndexError and KeyError. You can also pass a default that covers the entire operation, should the lookup fail at any level. Args: root: The target nesting of dictionaries, lists, or other objects supporting ``__getitem__``. path (tuple): A list of strings and integers to be successively looked up within *root*. default: The value to be returned should any ``PathAccessError`` exceptions be raised. """ if isinstance(path, basestring): path = path.split('.') cur = root try: for seg in path: try: cur = cur[seg] except (KeyError, IndexError) as exc: raise PathAccessError(exc, seg, path) except TypeError as exc: # either string index in a list, or a parent that # doesn't support indexing try: seg = int(seg) cur = cur[seg] except (ValueError, KeyError, IndexError, TypeError): if not is_iterable(cur): exc = TypeError('%r object is not indexable' % type(cur).__name__) raise PathAccessError(exc, seg, path) except PathAccessError: if default is _UNSET: raise return default return cur
[docs]def research(root, query=lambda p, k, v: True, reraise=False): """The :func:`research` function uses :func:`remap` to recurse over any data nested in *root*, and find values which match a given criterion, specified by the *query* callable. Results are returned as a list of ``(path, value)`` pairs. The paths are tuples in the same format accepted by :func:`get_path`. This can be useful for comparing values nested in two or more different structures. Here's a simple example that finds all integers: >>> root = {'a': {'b': 1, 'c': (2, 'd', 3)}, 'e': None} >>> res = research(root, query=lambda p, k, v: isinstance(v, int)) >>> print(sorted(res)) [(('a', 'b'), 1), (('a', 'c', 0), 2), (('a', 'c', 2), 3)] Note how *query* follows the same, familiar ``path, key, value`` signature as the ``visit`` and ``enter`` functions on :func:`remap`, and returns a :class:`bool`. Args: root: The target object to search. Supports the same types of objects as :func:`remap`, including :class:`list`, :class:`tuple`, :class:`dict`, and :class:`set`. query (callable): The function called on every object to determine whether to include it in the search results. The callable must accept three arguments, *path*, *key*, and *value*, commonly abbreviated *p*, *k*, and *v*, same as *enter* and *visit* from :func:`remap`. reraise (bool): Whether to reraise exceptions raised by *query* or to simply drop the result that caused the error. With :func:`research` it's easy to inspect the details of a data structure, like finding values that are at a certain depth (using ``len(p)``) and much more. If more advanced functionality is needed, check out the code and make your own :func:`remap` wrapper, and consider `submitting a patch`_! .. _submitting a patch: """ ret = [] if not callable(query): raise TypeError('query expected callable, not: %r' % query) def enter(path, key, value): try: if query(path, key, value): ret.append((path + (key,), value)) except Exception: if reraise: raise return default_enter(path, key, value) remap(root, enter=enter) return ret
# TODO: recollect() # TODO: refilter() # TODO: reiter() # GUID iterators: 10x faster and somewhat more compact than uuid. class GUIDerator(object): """The GUIDerator is an iterator that yields a globally-unique identifier (GUID) on every iteration. The GUIDs produced are hexadecimal strings. Testing shows it to be around 12x faster than the uuid module. By default it is also more compact, partly due to its default 96-bit (24-hexdigit) length. 96 bits of randomness means that there is a 1 in 2 ^ 32 chance of collision after 2 ^ 64 iterations. If more or less uniqueness is desired, the *size* argument can be adjusted accordingly. Args: size (int): character length of the GUID, defaults to 24. Lengths between 20 and 36 are considered valid. The GUIDerator has built-in fork protection that causes it to detect a fork on next iteration and reseed accordingly. """ def __init__(self, size=24): self.size = size if size < 20 or size > 36: raise ValueError('expected 20 < size <= 36') self.count = itertools.count() self.reseed() def reseed(self): = os.getpid() self.salt = '-'.join([str(, socket.gethostname() or b'<nohostname>', str(time.time()), codecs.encode(os.urandom(6), 'hex_codec').decode('ascii')]) # that codecs trick is the best/only way to get a bytes to # hexbytes in py2/3 return def __iter__(self): return self if _IS_PY3: def __next__(self): if os.getpid() != self.reseed() target_bytes = (self.salt + str(next(self.count))).encode('utf8') hash_text = hashlib.sha1(target_bytes).hexdigest()[:self.size] return hash_text else: def __next__(self): if os.getpid() != self.reseed() return hashlib.sha1(self.salt + str(next(self.count))).hexdigest()[:self.size] next = __next__ class SequentialGUIDerator(GUIDerator): """Much like the standard GUIDerator, the SequentialGUIDerator is an iterator that yields a globally-unique identifier (GUID) on every iteration. The GUIDs produced are hexadecimal strings. The SequentialGUIDerator differs in that it picks a starting GUID value and increments every iteration. This yields GUIDs which are of course unique, but also ordered and lexicographically sortable. The SequentialGUIDerator is aronud 50% faster than the normal GUIDerator, making it almost 20x as fast as the built-in uuid module. By default it is also more compact, partly due to its 96-bit (24-hexdigit) default length. 96 bits of randomness means that there is a 1 in 2 ^ 32 chance of collision after 2 ^ 64 iterations. If more or less uniqueness is desired, the *size* argument can be adjusted accordingly. Args: size (int): character length of the GUID, defaults to 24. Note that with SequentialGUIDerator there is a chance of GUIDs growing larger than the size configured. The SequentialGUIDerator has built-in fork protection that causes it to detect a fork on next iteration and reseed accordingly. """ if _IS_PY3: def reseed(self): super(SequentialGUIDerator, self).reseed() start_str = hashlib.sha1(self.salt.encode('utf8')).hexdigest() self.start = int(start_str[:self.size], 16) self.start |= (1 << ((self.size * 4) - 2)) else: def reseed(self): super(SequentialGUIDerator, self).reseed() start_str = hashlib.sha1(self.salt).hexdigest() self.start = int(start_str[:self.size], 16) self.start |= (1 << ((self.size * 4) - 2)) def __next__(self): if os.getpid() != self.reseed() return '%x' % (next(self.count) + self.start) next = __next__ guid_iter = GUIDerator() seq_guid_iter = SequentialGUIDerator() """ May actually be faster to do an isinstance check for a str path $ python -m timeit -s "x = [1]" "x[0]" 10000000 loops, best of 3: 0.0207 usec per loop $ python -m timeit -s "x = [1]" "try: x[0] \nexcept: pass" 10000000 loops, best of 3: 0.029 usec per loop $ python -m timeit -s "x = [1]" "try: x[1] \nexcept: pass" 1000000 loops, best of 3: 0.315 usec per loop # setting up try/except is fast, only around 0.01us # actually triggering the exception takes almost 10x as long $ python -m timeit -s "x = [1]" "isinstance(x, basestring)" 10000000 loops, best of 3: 0.141 usec per loop $ python -m timeit -s "x = [1]" "isinstance(x, str)" 10000000 loops, best of 3: 0.131 usec per loop $ python -m timeit -s "x = [1]" "try: x.split('.')\n except: pass" 1000000 loops, best of 3: 0.443 usec per loop $ python -m timeit -s "x = [1]" "try: x.split('.') \nexcept AttributeError: pass" 1000000 loops, best of 3: 0.544 usec per loop """