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# SOME DESCRIPTIVE TITLE.
# Copyright (C) 2001 Python Software Foundation
# This file is distributed under the same license as the Python package.
# FIRST AUTHOR <EMAIL@ADDRESS>, YEAR.
#
# Translators:
# python-doc bot, 2025
#
#, fuzzy
msgid ""
msgstr ""
"Project-Id-Version: Python 3.14\n"
"Report-Msgid-Bugs-To: \n"
"POT-Creation-Date: 2026-02-25 14:44+0000\n"
"PO-Revision-Date: 2025-09-16 00:00+0000\n"
"Last-Translator: python-doc bot, 2025\n"
"Language-Team: Japanese (https://app.transifex.com/python-doc/teams/5390/"
"ja/)\n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"
"Language: ja\n"
"Plural-Forms: nplurals=1; plural=0;\n"
#: ../../howto/mro.rst:4
msgid "The Python 2.3 Method Resolution Order"
msgstr ""
#: ../../howto/mro.rst:8
msgid ""
"This is a historical document, provided as an appendix to the official "
"documentation. The Method Resolution Order discussed here was *introduced* "
"in Python 2.3, but it is still used in later versions -- including Python 3."
msgstr ""
#: ../../howto/mro.rst:13
msgid "By `Michele Simionato <https://www.phyast.pitt.edu/~micheles/>`__."
msgstr ""
#: ../../howto/mro.rst:0
msgid "Abstract"
msgstr "概要"
#: ../../howto/mro.rst:17
msgid ""
"*This document is intended for Python programmers who want to understand the "
"C3 Method Resolution Order used in Python 2.3. Although it is not intended "
"for newbies, it is quite pedagogical with many worked out examples. I am "
"not aware of other publicly available documents with the same scope, "
"therefore it should be useful.*"
msgstr ""
#: ../../howto/mro.rst:23
msgid "Disclaimer:"
msgstr ""
#: ../../howto/mro.rst:25
msgid ""
"*I donate this document to the Python Software Foundation, under the Python "
"2.3 license. As usual in these circumstances, I warn the reader that what "
"follows* should *be correct, but I don't give any warranty. Use it at your "
"own risk and peril!*"
msgstr ""
#: ../../howto/mro.rst:30
msgid "Acknowledgments:"
msgstr ""
#: ../../howto/mro.rst:32
msgid ""
"*All the people of the Python mailing list who sent me their support. Paul "
"Foley who pointed out various imprecisions and made me to add the part on "
"local precedence ordering. David Goodger for help with the formatting in "
"reStructuredText. David Mertz for help with the editing. Finally, Guido van "
"Rossum who enthusiastically added this document to the official Python 2.3 "
"home-page.*"
msgstr ""
#: ../../howto/mro.rst:40
msgid "The beginning"
msgstr ""
#: ../../howto/mro.rst:42
msgid "*Felix qui potuit rerum cognoscere causas* -- Virgilius"
msgstr ""
#: ../../howto/mro.rst:44
msgid ""
"Everything started with a post by Samuele Pedroni to the Python development "
"mailing list [#]_. In his post, Samuele showed that the Python 2.2 method "
"resolution order is not monotonic and he proposed to replace it with the C3 "
"method resolution order. Guido agreed with his arguments and therefore now "
"Python 2.3 uses C3. The C3 method itself has nothing to do with Python, "
"since it was invented by people working on Dylan and it is described in a "
"paper intended for lispers [#]_. The present paper gives a (hopefully) "
"readable discussion of the C3 algorithm for Pythonistas who want to "
"understand the reasons for the change."
msgstr ""
#: ../../howto/mro.rst:55
msgid ""
"First of all, let me point out that what I am going to say only applies to "
"the *new style classes* introduced in Python 2.2: *classic classes* "
"maintain their old method resolution order, depth first and then left to "
"right. Therefore, there is no breaking of old code for classic classes; and "
"even if in principle there could be breaking of code for Python 2.2 new "
"style classes, in practice the cases in which the C3 resolution order "
"differs from the Python 2.2 method resolution order are so rare that no real "
"breaking of code is expected. Therefore:"
msgstr ""
#: ../../howto/mro.rst:64
msgid "*Don't be scared!*"
msgstr ""
#: ../../howto/mro.rst:66
msgid ""
"Moreover, unless you make strong use of multiple inheritance and you have "
"non-trivial hierarchies, you don't need to understand the C3 algorithm, and "
"you can easily skip this paper. On the other hand, if you really want to "
"know how multiple inheritance works, then this paper is for you. The good "
"news is that things are not as complicated as you might expect."
msgstr ""
#: ../../howto/mro.rst:73
msgid "Let me begin with some basic definitions."
msgstr ""
#: ../../howto/mro.rst:75
msgid ""
"Given a class C in a complicated multiple inheritance hierarchy, it is a non-"
"trivial task to specify the order in which methods are overridden, i.e. to "
"specify the order of the ancestors of C."
msgstr ""
#: ../../howto/mro.rst:79
msgid ""
"The list of the ancestors of a class C, including the class itself, ordered "
"from the nearest ancestor to the furthest, is called the class precedence "
"list or the *linearization* of C."
msgstr ""
#: ../../howto/mro.rst:83
msgid ""
"The *Method Resolution Order* (MRO) is the set of rules that construct the "
"linearization. In the Python literature, the idiom \"the MRO of C\" is also "
"used as a synonymous for the linearization of the class C."
msgstr ""
#: ../../howto/mro.rst:88
msgid ""
"For instance, in the case of single inheritance hierarchy, if C is a "
"subclass of C1, and C1 is a subclass of C2, then the linearization of C is "
"simply the list [C, C1 , C2]. However, with multiple inheritance "
"hierarchies, the construction of the linearization is more cumbersome, since "
"it is more difficult to construct a linearization that respects *local "
"precedence ordering* and *monotonicity*."
msgstr ""
#: ../../howto/mro.rst:96
msgid ""
"I will discuss the local precedence ordering later, but I can give the "
"definition of monotonicity here. A MRO is monotonic when the following is "
"true: *if C1 precedes C2 in the linearization of C, then C1 precedes C2 in "
"the linearization of any subclass of C*. Otherwise, the innocuous operation "
"of deriving a new class could change the resolution order of methods, "
"potentially introducing very subtle bugs. Examples where this happens will "
"be shown later."
msgstr ""
#: ../../howto/mro.rst:104
msgid ""
"Not all classes admit a linearization. There are cases, in complicated "
"hierarchies, where it is not possible to derive a class such that its "
"linearization respects all the desired properties."
msgstr ""
#: ../../howto/mro.rst:108
msgid "Here I give an example of this situation. Consider the hierarchy"
msgstr ""
#: ../../howto/mro.rst:116
msgid ""
"which can be represented with the following inheritance graph, where I have "
"denoted with O the ``object`` class, which is the beginning of any hierarchy "
"for new style classes:"
msgstr ""
#: ../../howto/mro.rst:120
msgid ""
" -----------\n"
"| |\n"
"| O |\n"
"| / \\ |\n"
" - X Y /\n"
" | / | /\n"
" | / |/\n"
" A B\n"
" \\ /\n"
" ?"
msgstr ""
#: ../../howto/mro.rst:133
msgid ""
"In this case, it is not possible to derive a new class C from A and B, since "
"X precedes Y in A, but Y precedes X in B, therefore the method resolution "
"order would be ambiguous in C."
msgstr ""
#: ../../howto/mro.rst:137
msgid ""
"Python 2.3 raises an exception in this situation (TypeError: MRO conflict "
"among bases Y, X) forbidding the naive programmer from creating ambiguous "
"hierarchies. Python 2.2 instead does not raise an exception, but chooses an "
"*ad hoc* ordering (CABXYO in this case)."
msgstr ""
#: ../../howto/mro.rst:143
msgid "The C3 Method Resolution Order"
msgstr ""
#: ../../howto/mro.rst:145
msgid ""
"Let me introduce a few simple notations which will be useful for the "
"following discussion. I will use the shortcut notation::"
msgstr ""
#: ../../howto/mro.rst:148
msgid "C1 C2 ... CN"
msgstr ""
#: ../../howto/mro.rst:150
msgid "to indicate the list of classes [C1, C2, ... , CN]."
msgstr ""
#: ../../howto/mro.rst:152
msgid "The *head* of the list is its first element::"
msgstr ""
#: ../../howto/mro.rst:154
msgid "head = C1"
msgstr ""
#: ../../howto/mro.rst:156
msgid "whereas the *tail* is the rest of the list::"
msgstr ""
#: ../../howto/mro.rst:158
msgid "tail = C2 ... CN."
msgstr ""
#: ../../howto/mro.rst:160
msgid "I shall also use the notation::"
msgstr ""
#: ../../howto/mro.rst:162
msgid "C + (C1 C2 ... CN) = C C1 C2 ... CN"
msgstr ""
#: ../../howto/mro.rst:164
msgid "to denote the sum of the lists [C] + [C1, C2, ... ,CN]."
msgstr ""
#: ../../howto/mro.rst:166
msgid "Now I can explain how the MRO works in Python 2.3."
msgstr ""
#: ../../howto/mro.rst:168
msgid ""
"Consider a class C in a multiple inheritance hierarchy, with C inheriting "
"from the base classes B1, B2, ... , BN. We want to compute the "
"linearization L[C] of the class C. The rule is the following:"
msgstr ""
#: ../../howto/mro.rst:173
msgid ""
"*the linearization of C is the sum of C plus the merge of the linearizations "
"of the parents and the list of the parents.*"
msgstr ""
#: ../../howto/mro.rst:176
msgid "In symbolic notation::"
msgstr ""
#: ../../howto/mro.rst:178
msgid "L[C(B1 ... BN)] = C + merge(L[B1] ... L[BN], B1 ... BN)"
msgstr ""
#: ../../howto/mro.rst:180
msgid ""
"In particular, if C is the ``object`` class, which has no parents, the "
"linearization is trivial::"
msgstr ""
#: ../../howto/mro.rst:183
msgid "L[object] = object."
msgstr ""
#: ../../howto/mro.rst:185
msgid ""
"However, in general one has to compute the merge according to the following "
"prescription:"
msgstr ""
#: ../../howto/mro.rst:188
msgid ""
"*take the head of the first list, i.e L[B1][0]; if this head is not in the "
"tail of any of the other lists, then add it to the linearization of C and "
"remove it from the lists in the merge, otherwise look at the head of the "
"next list and take it, if it is a good head. Then repeat the operation "
"until all the class are removed or it is impossible to find good heads. In "
"this case, it is impossible to construct the merge, Python 2.3 will refuse "
"to create the class C and will raise an exception.*"
msgstr ""
#: ../../howto/mro.rst:197
msgid ""
"This prescription ensures that the merge operation *preserves* the ordering, "
"if the ordering can be preserved. On the other hand, if the order cannot be "
"preserved (as in the example of serious order disagreement discussed above) "
"then the merge cannot be computed."
msgstr ""
#: ../../howto/mro.rst:202
msgid ""
"The computation of the merge is trivial if C has only one parent (single "
"inheritance); in this case::"
msgstr ""
#: ../../howto/mro.rst:205
msgid "L[C(B)] = C + merge(L[B],B) = C + L[B]"
msgstr ""
#: ../../howto/mro.rst:207
msgid ""
"However, in the case of multiple inheritance things are more cumbersome and "
"I don't expect you can understand the rule without a couple of examples ;-)"
msgstr ""
#: ../../howto/mro.rst:212
msgid "Examples"
msgstr "使用例"
#: ../../howto/mro.rst:214
msgid "First example. Consider the following hierarchy:"
msgstr ""
#: ../../howto/mro.rst:224
msgid "In this case the inheritance graph can be drawn as:"
msgstr ""
#: ../../howto/mro.rst:226
msgid ""
" 6\n"
" ---\n"
"Level 3 | O | (more general)\n"
" / --- \\\n"
" / | \\ |\n"
" / | \\ |\n"
" / | \\ |\n"
" --- --- --- |\n"
"Level 2 3 | D | 4| E | | F | 5 |\n"
" --- --- --- |\n"
" \\ \\ _ / | |\n"
" \\ / \\ _ | |\n"
" \\ / \\ | |\n"
" --- --- |\n"
"Level 1 1 | B | | C | 2 |\n"
" --- --- |\n"
" \\ / |\n"
" \\ / \\ /\n"
" ---\n"
"Level 0 0 | A | (more specialized)\n"
" ---"
msgstr ""
#: ../../howto/mro.rst:251
msgid "The linearizations of O,D,E and F are trivial::"
msgstr ""
#: ../../howto/mro.rst:253
msgid ""
"L[O] = O\n"
"L[D] = D O\n"
"L[E] = E O\n"
"L[F] = F O"
msgstr ""
#: ../../howto/mro.rst:258
msgid "The linearization of B can be computed as::"
msgstr ""
#: ../../howto/mro.rst:260
msgid "L[B] = B + merge(DO, EO, DE)"
msgstr ""
#: ../../howto/mro.rst:262
msgid ""
"We see that D is a good head, therefore we take it and we are reduced to "
"compute ``merge(O,EO,E)``. Now O is not a good head, since it is in the "
"tail of the sequence EO. In this case the rule says that we have to skip to "
"the next sequence. Then we see that E is a good head; we take it and we are "
"reduced to compute ``merge(O,O)`` which gives O. Therefore::"
msgstr ""
#: ../../howto/mro.rst:268
msgid "L[B] = B D E O"
msgstr ""
#: ../../howto/mro.rst:270
msgid "Using the same procedure one finds::"
msgstr ""
#: ../../howto/mro.rst:272
msgid ""
"L[C] = C + merge(DO,FO,DF)\n"
" = C + D + merge(O,FO,F)\n"
" = C + D + F + merge(O,O)\n"
" = C D F O"
msgstr ""
#: ../../howto/mro.rst:277
msgid "Now we can compute::"
msgstr ""
#: ../../howto/mro.rst:279
msgid ""
"L[A] = A + merge(BDEO,CDFO,BC)\n"
" = A + B + merge(DEO,CDFO,C)\n"
" = A + B + C + merge(DEO,DFO)\n"
" = A + B + C + D + merge(EO,FO)\n"
" = A + B + C + D + E + merge(O,FO)\n"
" = A + B + C + D + E + F + merge(O,O)\n"
" = A B C D E F O"
msgstr ""
#: ../../howto/mro.rst:287
msgid ""
"In this example, the linearization is ordered in a pretty nice way according "
"to the inheritance level, in the sense that lower levels (i.e. more "
"specialized classes) have higher precedence (see the inheritance graph). "
"However, this is not the general case."
msgstr ""
#: ../../howto/mro.rst:292
msgid ""
"I leave as an exercise for the reader to compute the linearization for my "
"second example:"
msgstr ""
#: ../../howto/mro.rst:303
msgid ""
"The only difference with the previous example is the change B(D,E) --> B(E,"
"D); however even such a little modification completely changes the ordering "
"of the hierarchy:"
msgstr ""
#: ../../howto/mro.rst:307
msgid ""
" 6\n"
" ---\n"
"Level 3 | O |\n"
" / --- \\\n"
" / | \\\n"
" / | \\\n"
" / | \\\n"
" --- --- ---\n"
"Level 2 2 | E | 4 | D | | F | 5\n"
" --- --- ---\n"
" \\ / \\ /\n"
" \\ / \\ /\n"
" \\ / \\ /\n"
" --- ---\n"
"Level 1 1 | B | | C | 3\n"
" --- ---\n"
" \\ /\n"
" \\ /\n"
" ---\n"
"Level 0 0 | A |\n"
" ---"
msgstr ""
#: ../../howto/mro.rst:332
msgid ""
"Notice that the class E, which is in the second level of the hierarchy, "
"precedes the class C, which is in the first level of the hierarchy, i.e. E "
"is more specialized than C, even if it is in a higher level."
msgstr ""
#: ../../howto/mro.rst:336
msgid ""
"A lazy programmer can obtain the MRO directly from Python 2.2, since in this "
"case it coincides with the Python 2.3 linearization. It is enough to invoke "
"the :meth:`~type.mro` method of class A:"
msgstr ""
#: ../../howto/mro.rst:345
msgid ""
"Finally, let me consider the example discussed in the first section, "
"involving a serious order disagreement. In this case, it is straightforward "
"to compute the linearizations of O, X, Y, A and B:"
msgstr ""
#: ../../howto/mro.rst:349
msgid ""
"L[O] = 0\n"
"L[X] = X O\n"
"L[Y] = Y O\n"
"L[A] = A X Y O\n"
"L[B] = B Y X O"
msgstr ""
#: ../../howto/mro.rst:357
msgid ""
"However, it is impossible to compute the linearization for a class C that "
"inherits from A and B::"
msgstr ""
#: ../../howto/mro.rst:360
msgid ""
"L[C] = C + merge(AXYO, BYXO, AB)\n"
" = C + A + merge(XYO, BYXO, B)\n"
" = C + A + B + merge(XYO, YXO)"
msgstr ""
#: ../../howto/mro.rst:364
msgid ""
"At this point we cannot merge the lists XYO and YXO, since X is in the tail "
"of YXO whereas Y is in the tail of XYO: therefore there are no good heads "
"and the C3 algorithm stops. Python 2.3 raises an error and refuses to "
"create the class C."
msgstr ""
#: ../../howto/mro.rst:370
msgid "Bad Method Resolution Orders"
msgstr ""
#: ../../howto/mro.rst:372
msgid ""
"A MRO is *bad* when it breaks such fundamental properties as local "
"precedence ordering and monotonicity. In this section, I will show that "
"both the MRO for classic classes and the MRO for new style classes in Python "
"2.2 are bad."
msgstr ""
#: ../../howto/mro.rst:377
msgid ""
"It is easier to start with the local precedence ordering. Consider the "
"following example:"
msgstr ""
#: ../../howto/mro.rst:384
msgid "with inheritance diagram"
msgstr ""
#: ../../howto/mro.rst:386
msgid ""
" O\n"
" |\n"
"(buy spam) F\n"
" | \\\n"
" | E (buy eggs)\n"
" | /\n"
" G\n"
"\n"
" (buy eggs or spam ?)"
msgstr ""
#: ../../howto/mro.rst:399
msgid ""
"We see that class G inherits from F and E, with F *before* E: therefore we "
"would expect the attribute *G.remember2buy* to be inherited by *F."
"remember2buy* and not by *E.remember2buy*: nevertheless Python 2.2 gives"
msgstr ""
#: ../../howto/mro.rst:407
msgid ""
"This is a breaking of local precedence ordering since the order in the local "
"precedence list, i.e. the list of the parents of G, is not preserved in the "
"Python 2.2 linearization of G::"
msgstr ""
#: ../../howto/mro.rst:411
msgid "L[G,P22]= G E F object # F *follows* E"
msgstr ""
#: ../../howto/mro.rst:413
msgid ""
"One could argue that the reason why F follows E in the Python 2.2 "
"linearization is that F is less specialized than E, since F is the "
"superclass of E; nevertheless the breaking of local precedence ordering is "
"quite non-intuitive and error prone. This is particularly true since it is "
"a different from old style classes:"
msgstr ""
#: ../../howto/mro.rst:425
msgid ""
"In this case the MRO is GFEF and the local precedence ordering is preserved."
msgstr ""
#: ../../howto/mro.rst:428
msgid ""
"As a general rule, hierarchies such as the previous one should be avoided, "
"since it is unclear if F should override E or vice-versa. Python 2.3 solves "
"the ambiguity by raising an exception in the creation of class G, "
"effectively stopping the programmer from generating ambiguous hierarchies. "
"The reason for that is that the C3 algorithm fails when the merge::"
msgstr ""
#: ../../howto/mro.rst:435
msgid "merge(FO,EFO,FE)"
msgstr ""
#: ../../howto/mro.rst:437
msgid ""
"cannot be computed, because F is in the tail of EFO and E is in the tail of "
"FE."
msgstr ""
#: ../../howto/mro.rst:440
msgid ""
"The real solution is to design a non-ambiguous hierarchy, i.e. to derive G "
"from E and F (the more specific first) and not from F and E; in this case "
"the MRO is GEF without any doubt."
msgstr ""
#: ../../howto/mro.rst:444
msgid ""
" O\n"
" |\n"
" F (spam)\n"
" / |\n"
"(eggs) E |\n"
" \\ |\n"
" G\n"
" (eggs, no doubt)"
msgstr ""
#: ../../howto/mro.rst:456
msgid ""
"Python 2.3 forces the programmer to write good hierarchies (or, at least, "
"less error-prone ones)."
msgstr ""
#: ../../howto/mro.rst:459
msgid ""
"On a related note, let me point out that the Python 2.3 algorithm is smart "
"enough to recognize obvious mistakes, as the duplication of classes in the "
"list of parents:"
msgstr ""
#: ../../howto/mro.rst:469
msgid ""
"Python 2.2 (both for classic classes and new style classes) in this "
"situation, would not raise any exception."
msgstr ""
#: ../../howto/mro.rst:472
msgid ""
"Finally, I would like to point out two lessons we have learned from this "
"example:"
msgstr ""
#: ../../howto/mro.rst:475
msgid ""
"despite the name, the MRO determines the resolution order of attributes, not "
"only of methods;"
msgstr ""
#: ../../howto/mro.rst:478
msgid ""
"the default food for Pythonistas is spam ! (but you already knew that ;-)"
msgstr ""
#: ../../howto/mro.rst:481
msgid ""
"Having discussed the issue of local precedence ordering, let me now consider "
"the issue of monotonicity. My goal is to show that neither the MRO for "
"classic classes nor that for Python 2.2 new style classes is monotonic."
msgstr ""
#: ../../howto/mro.rst:486
msgid ""
"To prove that the MRO for classic classes is non-monotonic is rather "
"trivial, it is enough to look at the diamond diagram:"
msgstr ""
#: ../../howto/mro.rst:489
msgid ""
" C\n"
" / \\\n"
" / \\\n"
"A B\n"
" \\ /\n"
" \\ /\n"
" D"
msgstr ""
#: ../../howto/mro.rst:500
msgid "One easily discerns the inconsistency::"
msgstr ""
#: ../../howto/mro.rst:502
msgid ""
"L[B,P21] = B C # B precedes C : B's methods win\n"
"L[D,P21] = D A C B C # B follows C : C's methods win!"
msgstr ""
#: ../../howto/mro.rst:505
msgid ""
"On the other hand, there are no problems with the Python 2.2 and 2.3 MROs, "
"they give both::"
msgstr ""
#: ../../howto/mro.rst:508
msgid "L[D] = D A B C"
msgstr ""
#: ../../howto/mro.rst:510
msgid ""
"Guido points out in his essay [#]_ that the classic MRO is not so bad in "
"practice, since one can typically avoids diamonds for classic classes. But "
"all new style classes inherit from ``object``, therefore diamonds are "
"unavoidable and inconsistencies shows up in every multiple inheritance graph."
msgstr ""
#: ../../howto/mro.rst:516
msgid ""
"The MRO of Python 2.2 makes breaking monotonicity difficult, but not "
"impossible. The following example, originally provided by Samuele Pedroni, "
"shows that the MRO of Python 2.2 is non-monotonic:"
msgstr ""
#: ../../howto/mro.rst:530
msgid ""
"Here are the linearizations according to the C3 MRO (the reader should "
"verify these linearizations as an exercise and draw the inheritance "
"diagram ;-) ::"
msgstr ""
#: ../../howto/mro.rst:534
msgid ""
"L[A] = A O\n"
"L[B] = B O\n"
"L[C] = C O\n"
"L[D] = D O\n"
"L[E] = E O\n"
"L[K1]= K1 A B C O\n"
"L[K2]= K2 D B E O\n"
"L[K3]= K3 D A O\n"
"L[Z] = Z K1 K2 K3 D A B C E O"
msgstr ""
#: ../../howto/mro.rst:544
msgid ""
"Python 2.2 gives exactly the same linearizations for A, B, C, D, E, K1, K2 "
"and K3, but a different linearization for Z::"
msgstr ""
#: ../../howto/mro.rst:547
msgid "L[Z,P22] = Z K1 K3 A K2 D B C E O"
msgstr ""
#: ../../howto/mro.rst:549
msgid ""
"It is clear that this linearization is *wrong*, since A comes before D "
"whereas in the linearization of K3 A comes *after* D. In other words, in K3 "
"methods derived by D override methods derived by A, but in Z, which still is "
"a subclass of K3, methods derived by A override methods derived by D! This "
"is a violation of monotonicity. Moreover, the Python 2.2 linearization of Z "
"is also inconsistent with local precedence ordering, since the local "
"precedence list of the class Z is [K1, K2, K3] (K2 precedes K3), whereas in "
"the linearization of Z K2 *follows* K3. These problems explain why the 2.2 "
"rule has been dismissed in favor of the C3 rule."
msgstr ""
#: ../../howto/mro.rst:561
msgid "The end"
msgstr ""
#: ../../howto/mro.rst:563
msgid ""
"This section is for the impatient reader, who skipped all the previous "
"sections and jumped immediately to the end. This section is for the lazy "
"programmer too, who didn't want to exercise her/his brain. Finally, it is "
"for the programmer with some hubris, otherwise s/he would not be reading a "
"paper on the C3 method resolution order in multiple inheritance "
"hierarchies ;-) These three virtues taken all together (and *not* "
"separately) deserve a prize: the prize is a short Python 2.2 script that "
"allows you to compute the 2.3 MRO without risk to your brain. Simply change "
"the last line to play with the various examples I have discussed in this "
"paper.::"
msgstr ""
#: ../../howto/mro.rst:574
msgid ""
"#<mro.py>\n"
"\n"
"\"\"\"C3 algorithm by Samuele Pedroni (with readability enhanced by me)."
"\"\"\"\n"
"\n"
"class __metaclass__(type):\n"
" \"All classes are metamagically modified to be nicely printed\"\n"
" __repr__ = lambda cls: cls.__name__\n"
"\n"
"class ex_2:\n"
" \"Serious order disagreement\" #From Guido\n"
" class O: pass\n"
" class X(O): pass\n"
" class Y(O): pass\n"
" class A(X,Y): pass\n"
" class B(Y,X): pass\n"
" try:\n"
" class Z(A,B): pass #creates Z(A,B) in Python 2.2\n"
" except TypeError:\n"
" pass # Z(A,B) cannot be created in Python 2.3\n"
"\n"
"class ex_5:\n"
" \"My first example\"\n"
" class O: pass\n"
" class F(O): pass\n"
" class E(O): pass\n"
" class D(O): pass\n"
" class C(D,F): pass\n"
" class B(D,E): pass\n"
" class A(B,C): pass\n"
"\n"
"class ex_6:\n"
" \"My second example\"\n"
" class O: pass\n"
" class F(O): pass\n"
" class E(O): pass\n"
" class D(O): pass\n"
" class C(D,F): pass\n"
" class B(E,D): pass\n"
" class A(B,C): pass\n"
"\n"
"class ex_9:\n"
" \"Difference between Python 2.2 MRO and C3\" #From Samuele\n"
" class O: pass\n"
" class A(O): pass\n"
" class B(O): pass\n"
" class C(O): pass\n"
" class D(O): pass\n"
" class E(O): pass\n"
" class K1(A,B,C): pass\n"
" class K2(D,B,E): pass\n"
" class K3(D,A): pass\n"
" class Z(K1,K2,K3): pass\n"
"\n"
"def merge(seqs):\n"
" print '\\n\\nCPL[%s]=%s' % (seqs[0][0],seqs),\n"
" res = []; i=0\n"
" while 1:\n"
" nonemptyseqs=[seq for seq in seqs if seq]\n"
" if not nonemptyseqs: return res\n"
" i+=1; print '\\n',i,'round: candidates...',\n"
" for seq in nonemptyseqs: # find merge candidates among seq heads\n"
" cand = seq[0]; print ' ',cand,\n"
" nothead=[s for s in nonemptyseqs if cand in s[1:]]\n"
" if nothead: cand=None #reject candidate\n"
" else: break\n"
" if not cand: raise \"Inconsistent hierarchy\"\n"
" res.append(cand)\n"
" for seq in nonemptyseqs: # remove cand\n"
" if seq[0] == cand: del seq[0]\n"
"\n"
"def mro(C):\n"
" \"Compute the class precedence list (mro) according to C3\"\n"
" return merge([[C]]+map(mro,C.__bases__)+[list(C.__bases__)])\n"
"\n"
"def print_mro(C):\n"
" print '\\nMRO[%s]=%s' % (C,mro(C))\n"
" print '\\nP22 MRO[%s]=%s' % (C,C.mro())\n"
"\n"
"print_mro(ex_9.Z)\n"
"\n"
"#</mro.py>"
msgstr ""
#: ../../howto/mro.rst:656
msgid "That's all folks,"
msgstr ""
#: ../../howto/mro.rst:658
msgid "enjoy !"
msgstr ""
#: ../../howto/mro.rst:662
msgid "Resources"
msgstr ""
#: ../../howto/mro.rst:664
msgid ""
"The thread on python-dev started by Samuele Pedroni: https://mail.python.org/"
"pipermail/python-dev/2002-October/029035.html"
msgstr ""
#: ../../howto/mro.rst:667
msgid ""
"The paper *A Monotonic Superclass Linearization for Dylan*: https://doi."
"org/10.1145/236337.236343"
msgstr ""
#: ../../howto/mro.rst:670
msgid ""
"Guido van Rossum's essay, *Unifying types and classes in Python 2.2*: "
"https://web.archive.org/web/20140210194412/http://www.python.org/download/"
"releases/2.2.2/descrintro"
msgstr ""