diff --git a/Lib/heapq.py b/Lib/heapq.py new file mode 100644 index 000000000..0e3555cf9 --- /dev/null +++ b/Lib/heapq.py @@ -0,0 +1,601 @@ +"""Heap queue algorithm (a.k.a. priority queue). + +Heaps are arrays for which a[k] <= a[2*k+1] and a[k] <= a[2*k+2] for +all k, counting elements from 0. For the sake of comparison, +non-existing elements are considered to be infinite. The interesting +property of a heap is that a[0] is always its smallest element. + +Usage: + +heap = [] # creates an empty heap +heappush(heap, item) # pushes a new item on the heap +item = heappop(heap) # pops the smallest item from the heap +item = heap[0] # smallest item on the heap without popping it +heapify(x) # transforms list into a heap, in-place, in linear time +item = heapreplace(heap, item) # pops and returns smallest item, and adds + # new item; the heap size is unchanged + +Our API differs from textbook heap algorithms as follows: + +- We use 0-based indexing. This makes the relationship between the + index for a node and the indexes for its children slightly less + obvious, but is more suitable since Python uses 0-based indexing. + +- Our heappop() method returns the smallest item, not the largest. + +These two make it possible to view the heap as a regular Python list +without surprises: heap[0] is the smallest item, and heap.sort() +maintains the heap invariant! +""" + +# Original code by Kevin O'Connor, augmented by Tim Peters and Raymond Hettinger + +__about__ = """Heap queues + +[explanation by François Pinard] + +Heaps are arrays for which a[k] <= a[2*k+1] and a[k] <= a[2*k+2] for +all k, counting elements from 0. For the sake of comparison, +non-existing elements are considered to be infinite. The interesting +property of a heap is that a[0] is always its smallest element. + +The strange invariant above is meant to be an efficient memory +representation for a tournament. The numbers below are `k', not a[k]: + + 0 + + 1 2 + + 3 4 5 6 + + 7 8 9 10 11 12 13 14 + + 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 + + +In the tree above, each cell `k' is topping `2*k+1' and `2*k+2'. In +a usual binary tournament we see in sports, each cell is the winner +over the two cells it tops, and we can trace the winner down the tree +to see all opponents s/he had. However, in many computer applications +of such tournaments, we do not need to trace the history of a winner. +To be more memory efficient, when a winner is promoted, we try to +replace it by something else at a lower level, and the rule becomes +that a cell and the two cells it tops contain three different items, +but the top cell "wins" over the two topped cells. + +If this heap invariant is protected at all time, index 0 is clearly +the overall winner. The simplest algorithmic way to remove it and +find the "next" winner is to move some loser (let's say cell 30 in the +diagram above) into the 0 position, and then percolate this new 0 down +the tree, exchanging values, until the invariant is re-established. +This is clearly logarithmic on the total number of items in the tree. +By iterating over all items, you get an O(n ln n) sort. + +A nice feature of this sort is that you can efficiently insert new +items while the sort is going on, provided that the inserted items are +not "better" than the last 0'th element you extracted. This is +especially useful in simulation contexts, where the tree holds all +incoming events, and the "win" condition means the smallest scheduled +time. When an event schedule other events for execution, they are +scheduled into the future, so they can easily go into the heap. So, a +heap is a good structure for implementing schedulers (this is what I +used for my MIDI sequencer :-). + +Various structures for implementing schedulers have been extensively +studied, and heaps are good for this, as they are reasonably speedy, +the speed is almost constant, and the worst case is not much different +than the average case. However, there are other representations which +are more efficient overall, yet the worst cases might be terrible. + +Heaps are also very useful in big disk sorts. You most probably all +know that a big sort implies producing "runs" (which are pre-sorted +sequences, which size is usually related to the amount of CPU memory), +followed by a merging passes for these runs, which merging is often +very cleverly organised[1]. It is very important that the initial +sort produces the longest runs possible. Tournaments are a good way +to that. If, using all the memory available to hold a tournament, you +replace and percolate items that happen to fit the current run, you'll +produce runs which are twice the size of the memory for random input, +and much better for input fuzzily ordered. + +Moreover, if you output the 0'th item on disk and get an input which +may not fit in the current tournament (because the value "wins" over +the last output value), it cannot fit in the heap, so the size of the +heap decreases. The freed memory could be cleverly reused immediately +for progressively building a second heap, which grows at exactly the +same rate the first heap is melting. When the first heap completely +vanishes, you switch heaps and start a new run. Clever and quite +effective! + +In a word, heaps are useful memory structures to know. I use them in +a few applications, and I think it is good to keep a `heap' module +around. :-) + +-------------------- +[1] The disk balancing algorithms which are current, nowadays, are +more annoying than clever, and this is a consequence of the seeking +capabilities of the disks. On devices which cannot seek, like big +tape drives, the story was quite different, and one had to be very +clever to ensure (far in advance) that each tape movement will be the +most effective possible (that is, will best participate at +"progressing" the merge). Some tapes were even able to read +backwards, and this was also used to avoid the rewinding time. +Believe me, real good tape sorts were quite spectacular to watch! +From all times, sorting has always been a Great Art! :-) +""" + +__all__ = ['heappush', 'heappop', 'heapify', 'heapreplace', 'merge', + 'nlargest', 'nsmallest', 'heappushpop'] + +def heappush(heap, item): + """Push item onto heap, maintaining the heap invariant.""" + heap.append(item) + _siftdown(heap, 0, len(heap)-1) + +def heappop(heap): + """Pop the smallest item off the heap, maintaining the heap invariant.""" + lastelt = heap.pop() # raises appropriate IndexError if heap is empty + if heap: + returnitem = heap[0] + heap[0] = lastelt + _siftup(heap, 0) + return returnitem + return lastelt + +def heapreplace(heap, item): + """Pop and return the current smallest value, and add the new item. + + This is more efficient than heappop() followed by heappush(), and can be + more appropriate when using a fixed-size heap. Note that the value + returned may be larger than item! That constrains reasonable uses of + this routine unless written as part of a conditional replacement: + + if item > heap[0]: + item = heapreplace(heap, item) + """ + returnitem = heap[0] # raises appropriate IndexError if heap is empty + heap[0] = item + _siftup(heap, 0) + return returnitem + +def heappushpop(heap, item): + """Fast version of a heappush followed by a heappop.""" + if heap and heap[0] < item: + item, heap[0] = heap[0], item + _siftup(heap, 0) + return item + +def heapify(x): + """Transform list into a heap, in-place, in O(len(x)) time.""" + n = len(x) + # Transform bottom-up. The largest index there's any point to looking at + # is the largest with a child index in-range, so must have 2*i + 1 < n, + # or i < (n-1)/2. If n is even = 2*j, this is (2*j-1)/2 = j-1/2 so + # j-1 is the largest, which is n//2 - 1. If n is odd = 2*j+1, this is + # (2*j+1-1)/2 = j so j-1 is the largest, and that's again n//2-1. + for i in reversed(range(n//2)): + _siftup(x, i) + +def _heappop_max(heap): + """Maxheap version of a heappop.""" + lastelt = heap.pop() # raises appropriate IndexError if heap is empty + if heap: + returnitem = heap[0] + heap[0] = lastelt + _siftup_max(heap, 0) + return returnitem + return lastelt + +def _heapreplace_max(heap, item): + """Maxheap version of a heappop followed by a heappush.""" + returnitem = heap[0] # raises appropriate IndexError if heap is empty + heap[0] = item + _siftup_max(heap, 0) + return returnitem + +def _heapify_max(x): + """Transform list into a maxheap, in-place, in O(len(x)) time.""" + n = len(x) + for i in reversed(range(n//2)): + _siftup_max(x, i) + +# 'heap' is a heap at all indices >= startpos, except possibly for pos. pos +# is the index of a leaf with a possibly out-of-order value. Restore the +# heap invariant. +def _siftdown(heap, startpos, pos): + newitem = heap[pos] + # Follow the path to the root, moving parents down until finding a place + # newitem fits. + while pos > startpos: + parentpos = (pos - 1) >> 1 + parent = heap[parentpos] + if newitem < parent: + heap[pos] = parent + pos = parentpos + continue + break + heap[pos] = newitem + +# The child indices of heap index pos are already heaps, and we want to make +# a heap at index pos too. We do this by bubbling the smaller child of +# pos up (and so on with that child's children, etc) until hitting a leaf, +# then using _siftdown to move the oddball originally at index pos into place. +# +# We *could* break out of the loop as soon as we find a pos where newitem <= +# both its children, but turns out that's not a good idea, and despite that +# many books write the algorithm that way. During a heap pop, the last array +# element is sifted in, and that tends to be large, so that comparing it +# against values starting from the root usually doesn't pay (= usually doesn't +# get us out of the loop early). See Knuth, Volume 3, where this is +# explained and quantified in an exercise. +# +# Cutting the # of comparisons is important, since these routines have no +# way to extract "the priority" from an array element, so that intelligence +# is likely to be hiding in custom comparison methods, or in array elements +# storing (priority, record) tuples. Comparisons are thus potentially +# expensive. +# +# On random arrays of length 1000, making this change cut the number of +# comparisons made by heapify() a little, and those made by exhaustive +# heappop() a lot, in accord with theory. Here are typical results from 3 +# runs (3 just to demonstrate how small the variance is): +# +# Compares needed by heapify Compares needed by 1000 heappops +# -------------------------- -------------------------------- +# 1837 cut to 1663 14996 cut to 8680 +# 1855 cut to 1659 14966 cut to 8678 +# 1847 cut to 1660 15024 cut to 8703 +# +# Building the heap by using heappush() 1000 times instead required +# 2198, 2148, and 2219 compares: heapify() is more efficient, when +# you can use it. +# +# The total compares needed by list.sort() on the same lists were 8627, +# 8627, and 8632 (this should be compared to the sum of heapify() and +# heappop() compares): list.sort() is (unsurprisingly!) more efficient +# for sorting. + +def _siftup(heap, pos): + endpos = len(heap) + startpos = pos + newitem = heap[pos] + # Bubble up the smaller child until hitting a leaf. + childpos = 2*pos + 1 # leftmost child position + while childpos < endpos: + # Set childpos to index of smaller child. + rightpos = childpos + 1 + if rightpos < endpos and not heap[childpos] < heap[rightpos]: + childpos = rightpos + # Move the smaller child up. + heap[pos] = heap[childpos] + pos = childpos + childpos = 2*pos + 1 + # The leaf at pos is empty now. Put newitem there, and bubble it up + # to its final resting place (by sifting its parents down). + heap[pos] = newitem + _siftdown(heap, startpos, pos) + +def _siftdown_max(heap, startpos, pos): + 'Maxheap variant of _siftdown' + newitem = heap[pos] + # Follow the path to the root, moving parents down until finding a place + # newitem fits. + while pos > startpos: + parentpos = (pos - 1) >> 1 + parent = heap[parentpos] + if parent < newitem: + heap[pos] = parent + pos = parentpos + continue + break + heap[pos] = newitem + +def _siftup_max(heap, pos): + 'Maxheap variant of _siftup' + endpos = len(heap) + startpos = pos + newitem = heap[pos] + # Bubble up the larger child until hitting a leaf. + childpos = 2*pos + 1 # leftmost child position + while childpos < endpos: + # Set childpos to index of larger child. + rightpos = childpos + 1 + if rightpos < endpos and not heap[rightpos] < heap[childpos]: + childpos = rightpos + # Move the larger child up. + heap[pos] = heap[childpos] + pos = childpos + childpos = 2*pos + 1 + # The leaf at pos is empty now. Put newitem there, and bubble it up + # to its final resting place (by sifting its parents down). + heap[pos] = newitem + _siftdown_max(heap, startpos, pos) + +def merge(*iterables, key=None, reverse=False): + '''Merge multiple sorted inputs into a single sorted output. + + Similar to sorted(itertools.chain(*iterables)) but returns a generator, + does not pull the data into memory all at once, and assumes that each of + the input streams is already sorted (smallest to largest). + + >>> list(merge([1,3,5,7], [0,2,4,8], [5,10,15,20], [], [25])) + [0, 1, 2, 3, 4, 5, 5, 7, 8, 10, 15, 20, 25] + + If *key* is not None, applies a key function to each element to determine + its sort order. + + >>> list(merge(['dog', 'horse'], ['cat', 'fish', 'kangaroo'], key=len)) + ['dog', 'cat', 'fish', 'horse', 'kangaroo'] + + ''' + + h = [] + h_append = h.append + + if reverse: + _heapify = _heapify_max + _heappop = _heappop_max + _heapreplace = _heapreplace_max + direction = -1 + else: + _heapify = heapify + _heappop = heappop + _heapreplace = heapreplace + direction = 1 + + if key is None: + for order, it in enumerate(map(iter, iterables)): + try: + next = it.__next__ + h_append([next(), order * direction, next]) + except StopIteration: + pass + _heapify(h) + while len(h) > 1: + try: + while True: + value, order, next = s = h[0] + yield value + s[0] = next() # raises StopIteration when exhausted + _heapreplace(h, s) # restore heap condition + except StopIteration: + _heappop(h) # remove empty iterator + if h: + # fast case when only a single iterator remains + value, order, next = h[0] + yield value + yield from next.__self__ + return + + for order, it in enumerate(map(iter, iterables)): + try: + next = it.__next__ + value = next() + h_append([key(value), order * direction, value, next]) + except StopIteration: + pass + _heapify(h) + while len(h) > 1: + try: + while True: + key_value, order, value, next = s = h[0] + yield value + value = next() + s[0] = key(value) + s[2] = value + _heapreplace(h, s) + except StopIteration: + _heappop(h) + if h: + key_value, order, value, next = h[0] + yield value + yield from next.__self__ + + +# Algorithm notes for nlargest() and nsmallest() +# ============================================== +# +# Make a single pass over the data while keeping the k most extreme values +# in a heap. Memory consumption is limited to keeping k values in a list. +# +# Measured performance for random inputs: +# +# number of comparisons +# n inputs k-extreme values (average of 5 trials) % more than min() +# ------------- ---------------- --------------------- ----------------- +# 1,000 100 3,317 231.7% +# 10,000 100 14,046 40.5% +# 100,000 100 105,749 5.7% +# 1,000,000 100 1,007,751 0.8% +# 10,000,000 100 10,009,401 0.1% +# +# Theoretical number of comparisons for k smallest of n random inputs: +# +# Step Comparisons Action +# ---- -------------------------- --------------------------- +# 1 1.66 * k heapify the first k-inputs +# 2 n - k compare remaining elements to top of heap +# 3 k * (1 + lg2(k)) * ln(n/k) replace the topmost value on the heap +# 4 k * lg2(k) - (k/2) final sort of the k most extreme values +# +# Combining and simplifying for a rough estimate gives: +# +# comparisons = n + k * (log(k, 2) * log(n/k) + log(k, 2) + log(n/k)) +# +# Computing the number of comparisons for step 3: +# ----------------------------------------------- +# * For the i-th new value from the iterable, the probability of being in the +# k most extreme values is k/i. For example, the probability of the 101st +# value seen being in the 100 most extreme values is 100/101. +# * If the value is a new extreme value, the cost of inserting it into the +# heap is 1 + log(k, 2). +# * The probability times the cost gives: +# (k/i) * (1 + log(k, 2)) +# * Summing across the remaining n-k elements gives: +# sum((k/i) * (1 + log(k, 2)) for i in range(k+1, n+1)) +# * This reduces to: +# (H(n) - H(k)) * k * (1 + log(k, 2)) +# * Where H(n) is the n-th harmonic number estimated by: +# gamma = 0.5772156649 +# H(n) = log(n, e) + gamma + 1 / (2 * n) +# http://en.wikipedia.org/wiki/Harmonic_series_(mathematics)#Rate_of_divergence +# * Substituting the H(n) formula: +# comparisons = k * (1 + log(k, 2)) * (log(n/k, e) + (1/n - 1/k) / 2) +# +# Worst-case for step 3: +# ---------------------- +# In the worst case, the input data is reversed sorted so that every new element +# must be inserted in the heap: +# +# comparisons = 1.66 * k + log(k, 2) * (n - k) +# +# Alternative Algorithms +# ---------------------- +# Other algorithms were not used because they: +# 1) Took much more auxiliary memory, +# 2) Made multiple passes over the data. +# 3) Made more comparisons in common cases (small k, large n, semi-random input). +# See the more detailed comparison of approach at: +# http://code.activestate.com/recipes/577573-compare-algorithms-for-heapqsmallest + +def nsmallest(n, iterable, key=None): + """Find the n smallest elements in a dataset. + + Equivalent to: sorted(iterable, key=key)[:n] + """ + + # Short-cut for n==1 is to use min() + if n == 1: + it = iter(iterable) + sentinel = object() + result = min(it, default=sentinel, key=key) + return [] if result is sentinel else [result] + + # When n>=size, it's faster to use sorted() + try: + size = len(iterable) + except (TypeError, AttributeError): + pass + else: + if n >= size: + return sorted(iterable, key=key)[:n] + + # When key is none, use simpler decoration + if key is None: + it = iter(iterable) + # put the range(n) first so that zip() doesn't + # consume one too many elements from the iterator + result = [(elem, i) for i, elem in zip(range(n), it)] + if not result: + return result + _heapify_max(result) + top = result[0][0] + order = n + _heapreplace = _heapreplace_max + for elem in it: + if elem < top: + _heapreplace(result, (elem, order)) + top, _order = result[0] + order += 1 + result.sort() + return [elem for (elem, order) in result] + + # General case, slowest method + it = iter(iterable) + result = [(key(elem), i, elem) for i, elem in zip(range(n), it)] + if not result: + return result + _heapify_max(result) + top = result[0][0] + order = n + _heapreplace = _heapreplace_max + for elem in it: + k = key(elem) + if k < top: + _heapreplace(result, (k, order, elem)) + top, _order, _elem = result[0] + order += 1 + result.sort() + return [elem for (k, order, elem) in result] + +def nlargest(n, iterable, key=None): + """Find the n largest elements in a dataset. + + Equivalent to: sorted(iterable, key=key, reverse=True)[:n] + """ + + # Short-cut for n==1 is to use max() + if n == 1: + it = iter(iterable) + sentinel = object() + result = max(it, default=sentinel, key=key) + return [] if result is sentinel else [result] + + # When n>=size, it's faster to use sorted() + try: + size = len(iterable) + except (TypeError, AttributeError): + pass + else: + if n >= size: + return sorted(iterable, key=key, reverse=True)[:n] + + # When key is none, use simpler decoration + if key is None: + it = iter(iterable) + result = [(elem, i) for i, elem in zip(range(0, -n, -1), it)] + if not result: + return result + heapify(result) + top = result[0][0] + order = -n + _heapreplace = heapreplace + for elem in it: + if top < elem: + _heapreplace(result, (elem, order)) + top, _order = result[0] + order -= 1 + result.sort(reverse=True) + return [elem for (elem, order) in result] + + # General case, slowest method + it = iter(iterable) + result = [(key(elem), i, elem) for i, elem in zip(range(0, -n, -1), it)] + if not result: + return result + heapify(result) + top = result[0][0] + order = -n + _heapreplace = heapreplace + for elem in it: + k = key(elem) + if top < k: + _heapreplace(result, (k, order, elem)) + top, _order, _elem = result[0] + order -= 1 + result.sort(reverse=True) + return [elem for (k, order, elem) in result] + +# If available, use C implementation +try: + from _heapq import * +except ImportError: + pass +try: + from _heapq import _heapreplace_max +except ImportError: + pass +try: + from _heapq import _heapify_max +except ImportError: + pass +try: + from _heapq import _heappop_max +except ImportError: + pass + + +if __name__ == "__main__": + + import doctest + print(doctest.testmod()) diff --git a/Lib/operator.py b/Lib/operator.py index f21920064..0e2e53efc 100644 --- a/Lib/operator.py +++ b/Lib/operator.py @@ -1,15 +1,464 @@ +""" +Operator Interface + +This module exports a set of functions corresponding to the intrinsic +operators of Python. For example, operator.add(x, y) is equivalent +to the expression x+y. The function names are those used for special +methods; variants without leading and trailing '__' are also provided +for convenience. + +This is the pure Python implementation of the module. +""" + +__all__ = ['abs', 'add', 'and_', 'attrgetter', 'concat', 'contains', 'countOf', + 'delitem', 'eq', 'floordiv', 'ge', 'getitem', 'gt', 'iadd', 'iand', + 'iconcat', 'ifloordiv', 'ilshift', 'imatmul', 'imod', 'imul', + 'index', 'indexOf', 'inv', 'invert', 'ior', 'ipow', 'irshift', + 'is_', 'is_not', 'isub', 'itemgetter', 'itruediv', 'ixor', 'le', + 'length_hint', 'lshift', 'lt', 'matmul', 'methodcaller', 'mod', + 'mul', 'ne', 'neg', 'not_', 'or_', 'pos', 'pow', 'rshift', + 'setitem', 'sub', 'truediv', 'truth', 'xor'] + +from builtins import abs as _abs -# Comparison operations: +# Comparison Operations *******************************************************# + +def lt(a, b): + "Same as a < b." + return a < b + +def le(a, b): + "Same as a <= b." + return a <= b def eq(a, b): + "Same as a == b." return a == b - def ne(a, b): + "Same as a != b." return a != b - def ge(a, b): + "Same as a >= b." return a >= b +def gt(a, b): + "Same as a > b." + return a > b + +# Logical Operations **********************************************************# + +def not_(a): + "Same as not a." + return not a + +def truth(a): + "Return True if a is true, False otherwise." + return True if a else False + +def is_(a, b): + "Same as a is b." + return a is b + +def is_not(a, b): + "Same as a is not b." + return a is not b + +# Mathematical/Bitwise Operations *********************************************# + +def abs(a): + "Same as abs(a)." + return _abs(a) + +def add(a, b): + "Same as a + b." + return a + b + +def and_(a, b): + "Same as a & b." + return a & b + +def floordiv(a, b): + "Same as a // b." + return a // b + +def index(a): + "Same as a.__index__()." + return a.__index__() + +def inv(a): + "Same as ~a." + return ~a +invert = inv + +def lshift(a, b): + "Same as a << b." + return a << b + +def mod(a, b): + "Same as a % b." + return a % b + +def mul(a, b): + "Same as a * b." + return a * b + +def matmul(a, b): + "Same as a @ b." + return a @ b + +def neg(a): + "Same as -a." + return -a + +def or_(a, b): + "Same as a | b." + return a | b + +def pos(a): + "Same as +a." + return +a + +def pow(a, b): + "Same as a ** b." + return a ** b + +def rshift(a, b): + "Same as a >> b." + return a >> b + +def sub(a, b): + "Same as a - b." + return a - b + +def truediv(a, b): + "Same as a / b." + return a / b + +def xor(a, b): + "Same as a ^ b." + return a ^ b + +# Sequence Operations *********************************************************# + +def concat(a, b): + "Same as a + b, for a and b sequences." + if not hasattr(a, '__getitem__'): + msg = "'%s' object can't be concatenated" % type(a).__name__ + raise TypeError(msg) + return a + b + +def contains(a, b): + "Same as b in a (note reversed operands)." + return b in a + +def countOf(a, b): + "Return the number of times b occurs in a." + count = 0 + for i in a: + if i == b: + count += 1 + return count + +def delitem(a, b): + "Same as del a[b]." + del a[b] + +def getitem(a, b): + "Same as a[b]." + return a[b] + +def indexOf(a, b): + "Return the first index of b in a." + for i, j in enumerate(a): + if j == b: + return i + else: + raise ValueError('sequence.index(x): x not in sequence') + +def setitem(a, b, c): + "Same as a[b] = c." + a[b] = c + +def length_hint(obj, default=0): + """ + Return an estimate of the number of items in obj. + This is useful for presizing containers when building from an iterable. + + If the object supports len(), the result will be exact. Otherwise, it may + over- or under-estimate by an arbitrary amount. The result will be an + integer >= 0. + """ + if not isinstance(default, int): + msg = ("'%s' object cannot be interpreted as an integer" % + type(default).__name__) + raise TypeError(msg) + + try: + return len(obj) + except TypeError: + pass + + try: + hint = type(obj).__length_hint__ + except AttributeError: + return default + + try: + val = hint(obj) + except TypeError: + return default + if val is NotImplemented: + return default + if not isinstance(val, int): + msg = ('__length_hint__ must be integer, not %s' % + type(val).__name__) + raise TypeError(msg) + if val < 0: + msg = '__length_hint__() should return >= 0' + raise ValueError(msg) + return val + +# Generalized Lookup Objects **************************************************# + +class attrgetter: + """ + Return a callable object that fetches the given attribute(s) from its operand. + After f = attrgetter('name'), the call f(r) returns r.name. + After g = attrgetter('name', 'date'), the call g(r) returns (r.name, r.date). + After h = attrgetter('name.first', 'name.last'), the call h(r) returns + (r.name.first, r.name.last). + """ + __slots__ = ('_attrs', '_call') + + def __init__(self, attr, *attrs): + if not attrs: + if not isinstance(attr, str): + raise TypeError('attribute name must be a string') + self._attrs = (attr,) + names = attr.split('.') + def func(obj): + for name in names: + obj = getattr(obj, name) + return obj + self._call = func + else: + self._attrs = (attr,) + attrs + getters = tuple(map(attrgetter, self._attrs)) + def func(obj): + return tuple(getter(obj) for getter in getters) + self._call = func + + def __call__(self, obj): + return self._call(obj) + + def __repr__(self): + return '%s.%s(%s)' % (self.__class__.__module__, + self.__class__.__qualname__, + ', '.join(map(repr, self._attrs))) + + def __reduce__(self): + return self.__class__, self._attrs + +class itemgetter: + """ + Return a callable object that fetches the given item(s) from its operand. + After f = itemgetter(2), the call f(r) returns r[2]. + After g = itemgetter(2, 5, 3), the call g(r) returns (r[2], r[5], r[3]) + """ + __slots__ = ('_items', '_call') + + def __init__(self, item, *items): + if not items: + self._items = (item,) + def func(obj): + return obj[item] + self._call = func + else: + self._items = items = (item,) + items + def func(obj): + return tuple(obj[i] for i in items) + self._call = func + + def __call__(self, obj): + return self._call(obj) + + def __repr__(self): + return '%s.%s(%s)' % (self.__class__.__module__, + self.__class__.__name__, + ', '.join(map(repr, self._items))) + + def __reduce__(self): + return self.__class__, self._items + +class methodcaller: + """ + Return a callable object that calls the given method on its operand. + After f = methodcaller('name'), the call f(r) returns r.name(). + After g = methodcaller('name', 'date', foo=1), the call g(r) returns + r.name('date', foo=1). + """ + __slots__ = ('_name', '_args', '_kwargs') + + def __init__(*args, **kwargs): + if len(args) < 2: + msg = "methodcaller needs at least one argument, the method name" + raise TypeError(msg) + self = args[0] + self._name = args[1] + if not isinstance(self._name, str): + raise TypeError('method name must be a string') + self._args = args[2:] + self._kwargs = kwargs + + def __call__(self, obj): + return getattr(obj, self._name)(*self._args, **self._kwargs) + + def __repr__(self): + args = [repr(self._name)] + args.extend(map(repr, self._args)) + args.extend('%s=%r' % (k, v) for k, v in self._kwargs.items()) + return '%s.%s(%s)' % (self.__class__.__module__, + self.__class__.__name__, + ', '.join(args)) + + def __reduce__(self): + if not self._kwargs: + return self.__class__, (self._name,) + self._args + else: + from functools import partial + return partial(self.__class__, self._name, **self._kwargs), self._args + + +# In-place Operations *********************************************************# + +def iadd(a, b): + "Same as a += b." + a += b + return a + +def iand(a, b): + "Same as a &= b." + a &= b + return a + +def iconcat(a, b): + "Same as a += b, for a and b sequences." + if not hasattr(a, '__getitem__'): + msg = "'%s' object can't be concatenated" % type(a).__name__ + raise TypeError(msg) + a += b + return a + +def ifloordiv(a, b): + "Same as a //= b." + a //= b + return a + +def ilshift(a, b): + "Same as a <<= b." + a <<= b + return a + +def imod(a, b): + "Same as a %= b." + a %= b + return a + +def imul(a, b): + "Same as a *= b." + a *= b + return a + +def imatmul(a, b): + "Same as a @= b." + a @= b + return a + +def ior(a, b): + "Same as a |= b." + a |= b + return a + +def ipow(a, b): + "Same as a **= b." + a **=b + return a + +def irshift(a, b): + "Same as a >>= b." + a >>= b + return a + +def isub(a, b): + "Same as a -= b." + a -= b + return a + +def itruediv(a, b): + "Same as a /= b." + a /= b + return a + +def ixor(a, b): + "Same as a ^= b." + a ^= b + return a + + +try: + from _operator import * +except ImportError: + pass +else: + from _operator import __doc__ + +# All of these "__func__ = func" assignments have to happen after importing +# from _operator to make sure they're set to the right function +__lt__ = lt +__le__ = le +__eq__ = eq +__ne__ = ne +__ge__ = ge +__gt__ = gt +__not__ = not_ +__abs__ = abs +__add__ = add +__and__ = and_ +__floordiv__ = floordiv +__index__ = index +__inv__ = inv +__invert__ = invert +__lshift__ = lshift +__mod__ = mod +__mul__ = mul +__matmul__ = matmul +__neg__ = neg +__or__ = or_ +__pos__ = pos +__pow__ = pow +__rshift__ = rshift +__sub__ = sub +__truediv__ = truediv +__xor__ = xor +__concat__ = concat +__contains__ = contains +__delitem__ = delitem +__getitem__ = getitem +__setitem__ = setitem +__iadd__ = iadd +__iand__ = iand +__iconcat__ = iconcat +__ifloordiv__ = ifloordiv +__ilshift__ = ilshift +__imod__ = imod +__imul__ = imul +__imatmul__ = imatmul +__ior__ = ior +__ipow__ = ipow +__irshift__ = irshift +__isub__ = isub +__itruediv__ = itruediv +__ixor__ = ixor