-
-
Notifications
You must be signed in to change notification settings - Fork 397
/
word_char.pyx
843 lines (682 loc) · 24.6 KB
/
word_char.pyx
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
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
r"""
Fast word datatype using an array of unsigned char
"""
#*****************************************************************************
# Copyright (C) 2014 Vincent Delecroix <20100.delecroix@gmail.com>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 2 of the License, or
# (at your option) any later version.
# http://www.gnu.org/licenses/
#*****************************************************************************
from cysignals.memory cimport check_allocarray, sig_free
from cysignals.signals cimport sig_on, sig_off
include "sage/data_structures/bitset.pxi"
cimport cython
from cpython.object cimport Py_EQ, Py_NE
from sage.rings.integer cimport Integer, smallInteger
from sage.rings.rational cimport Rational
from libc.string cimport memcpy, memcmp
from sage.combinat.words.word_datatypes cimport WordDatatype
from sage.structure.richcmp cimport rich_to_bool_sgn
from cpython.number cimport PyIndex_Check, PyNumber_Check
from cpython.sequence cimport PySequence_Check
from cpython.slice cimport PySlice_GetIndicesEx
import itertools
# the maximum value of a size_t
cdef size_t SIZE_T_MAX = -(<size_t> 1)
def reversed_word_iterator(WordDatatype_char w):
r"""
This function exists only because it is not possible to use yield in the
special method ``__reversed__``.
EXAMPLES::
sage: W = Words([0,1,2])
sage: w = W([0,1,0,0,1,2])
sage: list(reversed(w)) # indirect doctest
[2, 1, 0, 0, 1, 0]
"""
cdef ssize_t i
for i in range(w._length-1, -1, -1):
yield w._data[i]
cdef class WordDatatype_char(WordDatatype):
r"""
A Fast class for words represented by an array ``unsigned char *``.
Currently, only handles letters in [0,255].
"""
cdef unsigned char * _data
cdef size_t _length
# _master is a just a reference to another Python object in case the finite
# word is just a slice of another one. But because Cython takes care of
# Python attributes *before* the call to __dealloc__ we need to duplicate
# the information.
cdef WordDatatype_char _master
cdef int _is_slice
def __cinit__(self):
r"""
Initialization of C attributes
TESTS::
sage: Words([0,1])([])
word:
"""
self._data = NULL
self._length = 0
self._is_slice = 0
def __init__(self, parent, data):
r"""
Constructor
TESTS::
sage: W = Words([0,1,2,3])
sage: W([0,1,2,3])
word: 0123
sage: W(iter([0,1,2,3]))
word: 0123
"""
self._parent = parent
if not PySequence_Check(data):
data = list(data)
if data:
self._set_data(data)
@cython.boundscheck(False) # assume that indexing will not cause any IndexErrors
@cython.wraparound(False) # not check not correctly handle negative indices
cdef _set_data(self, data):
r"""
set the attribute ._data and ._length from the sequence data
(usually data is a word, a tuple or a list)
"""
cdef size_t i
self._length = len(data)
self._data = <unsigned char *>check_allocarray(self._length, sizeof(unsigned char))
for i in range(self._length):
self._data[i] = data[i]
def __dealloc__(self):
r"""
Deallocate memory only if self uses it own memory.
Note that ``sig_free`` will not deallocate memory if self is the
master of another word.
"""
# it is strictly forbidden here to access _master here! (it will be set
# to None most of the time)
if self._is_slice == 0:
sig_free(self._data)
def __nonzero__(self):
r"""
Test whether the word is not empty.
EXAMPLES::
sage: W = Words([0,3,5])
sage: bool(W([0,3,3,5]))
True
sage: bool(W([]))
False
"""
return self._length != 0
def is_empty(self):
r"""
Return whether the word is empty.
EXAMPLES::
sage: W = Words([0,1,2])
sage: W([0,1,2,2]).is_empty()
False
sage: W([]).is_empty()
True
"""
return not self
def __len__(self):
r"""
Return the length of the word as a Python integer.
TESTS::
sage: W = Words([0,1,2,3])
sage: w = W([0,1,2,0,3,2,1])
sage: len(w)
7
sage: type(len(w))
<... 'int'>
"""
return self._length
def length(self):
r"""
Return the length of the word as a Sage integer.
EXAMPLES::
sage: W = Words([0,1,2,3,4])
sage: w = W([0,1,2,0,3,2,1])
sage: w.length()
7
sage: type(w.length())
<... 'sage.rings.integer.Integer'>
sage: type(len(w))
<... 'int'>
"""
return smallInteger(self._length)
def letters(self):
r"""
Return the list of letters that appear in this word, listed in the
order of first appearance.
EXAMPLES::
sage: W = Words(5)
sage: W([1,3,1,2,2,3,1]).letters()
[1, 3, 2]
"""
cdef bitset_t seen
bitset_init(seen, 256) # allocation + initialization to 0
cdef size_t i
cdef list res = []
cdef unsigned char letter
for i in range(self._length):
letter = self._data[i]
if not bitset_in(seen, letter):
bitset_add(seen, letter)
res.append(letter)
bitset_free(seen)
return res
cdef _new_c(self, unsigned char * data, size_t length, WordDatatype_char master):
r"""
TO DISCUSS: in Integer (sage.rings.integer) this method is actually an
external function. But we might want to have several possible inheritance.
"""
cdef type t = type(self)
cdef WordDatatype_char other = t.__new__(t)
other._data = data
other._master = master # can be None
other._is_slice = 0 if master is None else 1
other._length = length
other._parent = self._parent
return other
def __hash__(self):
r"""
Return the hash value.
EXAMPLES::
sage: W = Words([0,1,2])
sage: W([0,1,0,1,0,0,0], datatype='list').__hash__()
102060647
sage: W([0,1,0,1,0,0,0], datatype='char').__hash__()
102060647
"""
cdef int res = 5381
cdef size_t i
if self._hash is None:
for i in range(min(<size_t>1024, self._length)):
res = ((res << 5) + res) + self._data[i]
self._hash = res
return self._hash
def __richcmp__(self, other, int op):
r"""
INPUT:
- ``other`` -- a word (WordDatatype_char)
- ``op`` -- int, from 0 to 5
TESTS::
sage: W = Words(range(100))
sage: w = W(list(range(10)) * 2)
sage: w == w
True
sage: w != w
False
sage: w[:-1] != w[1:]
True
sage: w < w[1:] and w[1:] > w
True
sage: w > w[1:] or w[1:] < w
False
Testing that :trac:`21609` is fixed::
sage: w = Word([1,2], alphabet=[1,2])
sage: z = Word([1,1], alphabet=[1,2])
sage: (w<w, z<z, w<z, z<w)
(False, False, False, True)
sage: (w<=w, z<=z, w<=z, z<=w)
(True, True, False, True)
sage: (w==w, z==z, w==z, z==w)
(True, True, False, False)
sage: (w!=w, z!=z, w!=z, z!=w)
(False, False, True, True)
sage: (w>w, z>z, w>z, z>w)
(False, False, True, False)
sage: (w>=w, z>=z, w>=z, z>=w)
(True, True, True, False)
Testing that :trac:`22717` is fixed::
sage: w = Word([1,2], alphabet=[1,2,3])
sage: z = Word([1,2,3], alphabet=[1,2,3])
sage: (w<w, z<z, w<z, z<w)
(False, False, True, False)
sage: (w<=w, z<=z, w<=z, z<=w)
(True, True, True, False)
sage: (w==w, z==z, w==z, z==w)
(True, True, False, False)
sage: (w!=w, z!=z, w!=z, z!=w)
(False, False, True, True)
sage: (w>w, z>z, w>z, z>w)
(False, False, False, True)
sage: (w>=w, z>=z, w>=z, z>=w)
(True, True, False, True)
Check that :trac:`23317` is fixed::
sage: L = [Word([2,2], (1,2)), Word([], (1,2))]
sage: sorted(L)
[word: , word: 22]
"""
if not isinstance(other, WordDatatype_char):
return NotImplemented
cdef WordDatatype_char a = <WordDatatype_char>self
cdef WordDatatype_char b = <WordDatatype_char>other
# Words of different lengths are not equal!
if (op == Py_EQ or op == Py_NE) and a._length != b._length:
return op == Py_NE
# Compare overlapping chars
cdef size_t l = min(a._length, b._length)
sig_on()
cdef int test = memcmp(a._data, b._data, l)
sig_off()
if test == 0:
# Equality: compare lengths
test = a._length - b._length
return rich_to_bool_sgn(op, test)
def __getitem__(self, key):
r"""
INPUT:
- ``key`` -- index
TESTS::
sage: W = Words([0,1,2,3])
sage: w = W([0,1,0,2,0,3,1,2,3])
sage: w[0]
0
sage: w[2]
0
sage: w[1:]
word: 10203123
sage: w[5::-2]
word: 321
sage: w = W([randint(0,3) for _ in range(20)])
sage: list(w) == [w[i] for i in range(len(w))]
True
sage: w['foo':'bar']
Traceback (most recent call last):
...
TypeError: slice indices must be integers or None or have an __index__ method
Check a weird behavior of PySlice_GetIndicesEx (:trac:`17056`)::
sage: w[1:0]
word:
"""
cdef Py_ssize_t i, start, stop, step, slicelength
cdef unsigned char * data
cdef size_t j,k
if isinstance(key, slice):
# here the key is a slice
PySlice_GetIndicesEx(key,
self._length,
&start, &stop, &step,
&slicelength)
if slicelength == 0:
return self._new_c(NULL, 0, None)
if step == 1:
return self._new_c(self._data+start, stop-start, self)
data = <unsigned char *>check_allocarray(slicelength, sizeof(unsigned char))
j = 0
for k in range(start,stop,step):
data[j] = self._data[k]
j += 1
return self._new_c(data, slicelength, None)
elif PyIndex_Check(key):
# here the key is an int
i = key # cast key into a size_t
if i < 0:
i += self._length;
if i < 0 or <size_t>i >= self._length:
raise IndexError("word index out of range")
return self._data[i]
raise TypeError("word indices must be integers")
def __iter__(self):
r"""
Iterator over the letter of self
EXAMPLES::
sage: W = Words([0,1,2,3])
sage: list(W([0,0,1,0])) # indirect doctest
[0, 0, 1, 0]
"""
cdef size_t i
for i in range(self._length):
yield self._data[i]
def __reversed__(self):
r"""
Reversed iterator over the letter of self
EXAMPLES::
sage: W = Words([0,1,2,3])
sage: list(reversed(W([0,0,1,0]))) # indirect doctest
[0, 1, 0, 0]
TESTS::
sage: list(reversed(W([])))
[]
sage: list(reversed(W([1])))
[1]
"""
return reversed_word_iterator(self)
cdef _concatenate(self, WordDatatype_char other):
cdef unsigned char * data
data = <unsigned char *>check_allocarray(self._length + other._length, sizeof(unsigned char))
sig_on()
memcpy(data, self._data, self._length * sizeof(unsigned char))
memcpy(data+self._length, other._data, other._length * sizeof(unsigned char))
sig_off()
return self._new_c(data, self._length + other._length, None)
def __mul__(self, other):
r"""
Concatenation of ``self`` and ``other``.
TESTS:
sage: W = Words(IntegerRange(0,255))
sage: W([0,1]) * W([2,0])
word: 0120
The result is automatically converted to a WordDatatype_char. Currently we can
even do::
sage: w = W([0,1,2,3])
sage: w * [4,0,4,0]
word: 01234040
"""
cdef WordDatatype_char w
if isinstance(other, WordDatatype_char):
return (<WordDatatype_char> self)._concatenate(other)
elif PySequence_Check(other):
# we convert other to a WordDatatype_char and perform the concatenation
w = (<WordDatatype_char> self)._new_c(NULL, 0, None)
w._set_data(other)
return (<WordDatatype_char> self)._concatenate(w)
else:
from sage.combinat.words.finite_word import FiniteWord_class
return FiniteWord_class.concatenate(self, other)
def __add__(self, other):
r"""
Concatenation (alias for ``*``).
TESTS::
sage: W = Words([0,1,2])
sage: type(W([0]) + W([1])) is W.finite_words()._element_classes['char']
True
"""
return self * other
def concatenate(self, other):
r"""
Concatenation of ``self`` and ``other``.
EXAMPLES::
sage: W = Words([0,1,2])
sage: W([0,2,1]).concatenate([0,0,0])
word: 021000
TESTS::
sage: W = Words([0,1,2])
sage: w = W([0,2,1]).concatenate(W([0,0,0]))
sage: type(w) is W.finite_words()._element_classes['char']
True
"""
return self * other
def __pow__(self, exp, mod):
r"""
Power
INPUT:
- ``exp`` - an integer, a rational, a float number or plus infinity.
TESTS::
sage: W = Words(range(20))
sage: w = W([0,1,2,3])
sage: w
word: 0123
sage: w ** (1/2)
word: 01
sage: w ** 2
word: 01230123
sage: w ** 3
word: 012301230123
sage: w ** (7/2)
word: 01230123012301
sage: len(((w ** 2) ** 3) ** 5) == len(w) * 2 * 3 * 5
True
Infinite exponents::
sage: W([0,1]) ** Infinity
word: 0101010101010101010101010101010101010101...
"""
if not PyNumber_Check(exp):
raise ValueError("the exponent must be a number or infinity")
if mod is not None:
raise ValueError("a word can not be taken modulo")
if exp == float('inf'):
from sage.rings.infinity import Infinity
fcn = lambda n: self[n % self.length()]
return self._parent.shift()(fcn, datatype='callable')
if exp < 0:
raise ValueError("can not take negative power of a word")
cdef WordDatatype_char w = self
cdef size_t i, rest
if type(exp) is Rational:
if w._length % exp.denominator():
raise ValueError("undefined")
i = exp.floor()
rest = (exp - exp.floor()) * w._length
else:
i = exp
rest = 0
# first handle the cases (i*length + rest) <= length and return the
# corresponding prefix of self
if i == 1 and rest == 0:
return self
if w._length == 0:
return w._new_c(NULL, 0, None)
if i == 0:
if rest == 0:
return w._new_c(NULL, 0, None)
else:
return w._new_c(w._data, rest, self)
# now consider non trivial powers
if w._length > SIZE_T_MAX / (i+1):
raise OverflowError("the length of the result is too large")
cdef Py_ssize_t new_length = w._length * i + rest
cdef unsigned char * data = <unsigned char *>check_allocarray(new_length, sizeof(unsigned char))
cdef Py_ssize_t j = w._length
memcpy(data, w._data, j * sizeof(unsigned char))
while 2*j < new_length:
memcpy(data + j, data, j * sizeof(unsigned char))
j *= 2
memcpy(data + j, data, (new_length - j) * sizeof(unsigned char))
return w._new_c(data, new_length, None)
def has_prefix(self, other):
r"""
Test whether ``other`` is a prefix of ``self``.
INPUT:
- ``other`` -- a word or a sequence (e.g. tuple, list)
EXAMPLES::
sage: W = Words([0,1,2])
sage: w = W([0,1,1,0,1,2,0])
sage: w.has_prefix([0,1,1])
True
sage: w.has_prefix([0,1,2])
False
sage: w.has_prefix(w)
True
sage: w.has_prefix(w[:-1])
True
sage: w.has_prefix(w[1:])
False
TESTS:
:trac:`19322`::
sage: W = Words([0,1,2])
sage: w = W([0,1,0,2])
sage: w.has_prefix(words.FibonacciWord())
False
sage: w.has_prefix([0,1,0,2,0])
False
sage: w.has_prefix([0,1,0,2])
True
sage: w.has_prefix([0,1,0])
True
"""
cdef Py_ssize_t i
cdef WordDatatype_char w
if isinstance(other, WordDatatype_char):
# C level
w = <WordDatatype_char> other
if w._length > self._length:
return False
return memcmp(self._data, w._data, w._length * sizeof(unsigned char)) == 0
elif PySequence_Check(other):
# python level
from sage.combinat.words.infinite_word import InfiniteWord_class
if isinstance(other, InfiniteWord_class) or len(other) > len(self):
return False
for i in range(len(other)):
if other[i] != self[i]:
return False
return True
raise TypeError("not able to initialize a word from {}".format(other))
def is_square(self):
r"""
Return True if self is a square, and False otherwise.
EXAMPLES::
sage: w = Word([n % 4 for n in range(48)], alphabet=[0,1,2,3])
sage: w.is_square()
True
::
sage: w = Word([n % 4 for n in range(49)], alphabet=[0,1,2,3])
sage: w.is_square()
False
sage: (w*w).is_square()
True
TESTS:
The above tests correspond to the present class (char)::
sage: type(w)
<class 'sage.combinat.words.word.FiniteWord_char'>
::
sage: Word([], alphabet=[0,1]).is_square()
True
sage: Word([0], alphabet=[0,1]).is_square()
False
sage: Word([0,0], alphabet=[0,1]).is_square()
True
"""
cdef size_t l
if self._length % 2:
return False
else:
l = self._length // 2
return memcmp(self._data,
self._data + l,
l * sizeof(unsigned char)) == 0
def longest_common_prefix(self, other):
r"""
Return the longest common prefix of this word and ``other``.
EXAMPLES::
sage: W = Words([0,1,2])
sage: W([0,1,0,2]).longest_common_prefix([0,1])
word: 01
sage: u = W([0,1,0,0,1])
sage: v = W([0,1,0,2])
sage: u.longest_common_prefix(v)
word: 010
sage: v.longest_common_prefix(u)
word: 010
Using infinite words is also possible (and the return type is also a
of the same type as ``self``)::
sage: W([0,1,0,0]).longest_common_prefix(words.FibonacciWord())
word: 0100
sage: type(_)
<class 'sage.combinat.words.word.FiniteWord_char'>
An example of an intensive usage::
sage: W = Words([0,1])
sage: w = words.FibonacciWord()
sage: w = W(list(w[:5000]))
sage: L = [[len(w[n:].longest_common_prefix(w[n+fibonacci(i):]))
....: for i in range(5,15)] for n in range(1,1000)]
sage: for n,l in enumerate(L):
....: if l.count(0) > 4:
....: print("{} {}".format(n+1,l))
375 [0, 13, 0, 34, 0, 89, 0, 233, 0, 233]
376 [0, 12, 0, 33, 0, 88, 0, 232, 0, 232]
608 [8, 0, 21, 0, 55, 0, 144, 0, 377, 0]
609 [7, 0, 20, 0, 54, 0, 143, 0, 376, 0]
985 [0, 13, 0, 34, 0, 89, 0, 233, 0, 610]
986 [0, 12, 0, 33, 0, 88, 0, 232, 0, 609]
TESTS::
sage: W = Words([0,1,2])
sage: w = W([0,2,1,0,0,1])
sage: w.longest_common_prefix(0)
Traceback (most recent call last):
...
TypeError: unsupported input 0
::
sage: Word([2,2], (1,2)).longest_common_prefix([])
word:
"""
cdef WordDatatype_char w
cdef size_t i = <size_t>(-1)
cdef size_t m
if isinstance(other, WordDatatype_char):
# C level
# (this can be much faster if we allow to compare larger memory
# zones)
w = other
m = min(self._length, w._length)
for i in range(m):
if self._data[i] != w._data[i]:
break
else:
if self._length <= w._length:
return self
else:
return other
return self._new_c(self._data, i, self)
elif PySequence_Check(other):
# Python level
# we avoid to call len(other) since it might be an infinite word
for i, a in enumerate(itertools.islice(other, self._length)):
if self._data[i] != a:
break
else:
i += 1
return self._new_c(self._data, i, self)
raise TypeError("unsupported input {}".format(other))
def longest_common_suffix(self, other):
r"""
Return the longest common suffix between this word and ``other``.
EXAMPLES::
sage: W = Words([0,1,2])
sage: W([0,1,0,2]).longest_common_suffix([2,0,2])
word: 02
sage: u = W([0,1,0,0,1])
sage: v = W([1,2,0,0,1])
sage: u.longest_common_suffix(v)
word: 001
sage: v.longest_common_suffix(u)
word: 001
TESTS::
sage: W = Words([0,1,2])
sage: w = W([0,2,1,0,0,1])
sage: w.longest_common_suffix(0)
Traceback (most recent call last):
...
TypeError: unsupported input 0
::
sage: Word([2,2], (1,2)).longest_common_suffix([])
word:
"""
cdef WordDatatype_char w
cdef size_t i = <size_t>(-1)
cdef size_t m
cdef size_t lo
if isinstance(other, WordDatatype_char):
# C level
# (this can be much faster if we could compare larger memory
# zones)
w = other
m = min(self._length, w._length)
for i in range(m):
if self._data[self._length-i-1] != w._data[w._length-i-1]:
break
else:
if self._length <= w._length:
return self
else:
return other
return self._new_c(self._data+self._length-i, i, self)
elif PySequence_Check(other):
# Python level
lo = len(other)
m = min(self._length, lo)
for i in range(m):
if self._data[self._length-i-1] != other[lo-i-1]:
break
else:
if self._length == m:
return self
else:
i += 1
return self._new_c(self._data+self._length-i, i, self)
raise TypeError("unsupported input {}".format(other))