classes.po

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msgid ""
msgstr ""
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#: ../../tutorial/classes.rst:5
msgid "Classes"
msgstr "类"

#: ../../tutorial/classes.rst:7
msgid ""
"Classes provide a means of bundling data and functionality together.  "
"Creating a new class creates a new *type* of object, allowing new "
"*instances* of that type to be made.  Each class instance can have "
"attributes attached to it for maintaining its state.  Class instances can "
"also have methods (defined by its class) for modifying its state."
msgstr ""
"类提供了把数据和功能绑定在一起的方法。创建新类时创建了新的对象 *类型*，从而能够创建该类型的新 "
"*实例*。实例具有能维持自身状态的属性，还具有能修改自身状态的方法（由其所属的类来定义）。"

#: ../../tutorial/classes.rst:13
msgid ""
"Compared with other programming languages, Python's class mechanism adds "
"classes with a minimum of new syntax and semantics.  It is a mixture of the "
"class mechanisms found in C++ and Modula-3.  Python classes provide all the "
"standard features of Object Oriented Programming: the class inheritance "
"mechanism allows multiple base classes, a derived class can override any "
"methods of its base class or classes, and a method can call the method of a "
"base class with the same name.  Objects can contain arbitrary amounts and "
"kinds of data.  As is true for modules, classes partake of the dynamic "
"nature of Python: they are created at runtime, and can be modified further "
"after creation."
msgstr ""
"和其他编程语言相比，Python 的类只使用了很少的新语法和语义。Python 的类有点类似于 C++ 和 Modula-3 "
"中类的结合体，而且支持面向对象编程（OOP）的所有标准特性：类的继承机制支持多个基类、派生的类能覆盖基类的方法、类的方法能调用基类中的同名方法。对象可包含任意数量和类型的数据。和模块一样，类也支持"
" Python 动态特性：在运行时创建，创建后还可以修改。"

#: ../../tutorial/classes.rst:23
msgid ""
"In C++ terminology, normally class members (including the data members) are "
"*public* (except see below :ref:`tut-private`), and all member functions are"
" *virtual*.  As in Modula-3, there are no shorthands for referencing the "
"object's members from its methods: the method function is declared with an "
"explicit first argument representing the object, which is provided "
"implicitly by the call.  As in Smalltalk, classes themselves are objects.  "
"This provides semantics for importing and renaming.  Unlike C++ and "
"Modula-3, built-in types can be used as base classes for extension by the "
"user.  Also, like in C++, most built-in operators with special syntax "
"(arithmetic operators, subscripting etc.) can be redefined for class "
"instances."
msgstr ""
"如果用 C++ 术语来描述的话，类成员（包括数据成员）通常为 *public* （例外的情况见下文 :ref:`tut-"
"private`），所有成员函数都为 *virtual* 。与 Modula-3 "
"中一样，没有用于从对象的方法中引用本对象成员的简写形式：方法函数在声明时，有一个显式的第一个参数代表本对象，该参数由方法调用隐式提供。与在 "
"Smalltalk 中一样，Python 的类也是对象，这为导入和重命名提供了语义支持。与 C++ 和 Modula-3 不同，Python "
"的内置类型可以用作基类，供用户扩展。此外，与 C++ 一样，具有特殊语法的内置运算符（算术运算符、下标等）都可以为类实例重新定义。"

#: ../../tutorial/classes.rst:34
msgid ""
"(Lacking universally accepted terminology to talk about classes, I will make"
" occasional use of Smalltalk and C++ terms.  I would use Modula-3 terms, "
"since its object-oriented semantics are closer to those of Python than C++, "
"but I expect that few readers have heard of it.)"
msgstr ""
"由于缺乏关于类的公认术语，本章中偶尔会使用 Smalltalk 和 C++ 的术语。本章还会使用 Modula-3 的术语，Modula-3 "
"的面向对象语义比 C++ 更接近 Python，但估计听说过这门语言的读者很少。"

#: ../../tutorial/classes.rst:43
msgid "A Word About Names and Objects"
msgstr "名称和对象"

#: ../../tutorial/classes.rst:45
msgid ""
"Objects have individuality, and multiple names (in multiple scopes) can be "
"bound to the same object.  This is known as aliasing in other languages.  "
"This is usually not appreciated on a first glance at Python, and can be "
"safely ignored when dealing with immutable basic types (numbers, strings, "
"tuples).  However, aliasing has a possibly surprising effect on the "
"semantics of Python code involving mutable objects such as lists, "
"dictionaries, and most other types. This is usually used to the benefit of "
"the program, since aliases behave like pointers in some respects.  For "
"example, passing an object is cheap since only a pointer is passed by the "
"implementation; and if a function modifies an object passed as an argument, "
"the caller will see the change --- this eliminates the need for two "
"different argument passing mechanisms as in Pascal."
msgstr ""
"对象之间相互独立，多个名称（甚至是多个作用域内的多个名称）可以绑定到同一对象。这在其他语言中通常被称为别名。Python "
"初学者通常不容易理解这个概念，处理数字、字符串、元组等不可变基本类型时，可以不必理会。但是，对于涉及可变对象（如列表、字典，以及大多数其他类型）的 "
"Python "
"代码的语义，别名可能会产生意料之外的效果。这样做，通常是为了让程序受益，因为别名在某些方面就像指针。例如，传递对象的代价很小，因为实现只传递一个指针；如果函数修改了作为参数传递的对象，调用者就可以看到更改——无需像"
" Pascal 那样用两个不同的机制来传参。"

#: ../../tutorial/classes.rst:61
msgid "Python Scopes and Namespaces"
msgstr "Python 作用域和命名空间"

#: ../../tutorial/classes.rst:63
msgid ""
"Before introducing classes, I first have to tell you something about "
"Python's scope rules.  Class definitions play some neat tricks with "
"namespaces, and you need to know how scopes and namespaces work to fully "
"understand what's going on. Incidentally, knowledge about this subject is "
"useful for any advanced Python programmer."
msgstr ""
"在介绍类前，首先要介绍 Python "
"的作用域规则。类定义对命名空间有一些巧妙的技巧，了解作用域和命名空间的工作机制有利于加强对类的理解。并且，即便对于高级 Python "
"程序员，这方面的知识也很有用。"

#: ../../tutorial/classes.rst:69
msgid "Let's begin with some definitions."
msgstr "接下来，我们先了解一些定义。"

#: ../../tutorial/classes.rst:71
msgid ""
"A *namespace* is a mapping from names to objects.  Most namespaces are "
"currently implemented as Python dictionaries, but that's normally not "
"noticeable in any way (except for performance), and it may change in the "
"future.  Examples of namespaces are: the set of built-in names (containing "
"functions such as :func:`abs`, and built-in exception names); the global "
"names in a module; and the local names in a function invocation.  In a sense"
" the set of attributes of an object also form a namespace.  The important "
"thing to know about namespaces is that there is absolutely no relation "
"between names in different namespaces; for instance, two different modules "
"may both define a function ``maximize`` without confusion --- users of the "
"modules must prefix it with the module name."
msgstr ""
"*namespace* （命名空间）是从名称到对象的映射。现在，大多数命名空间都使用 Python "
"字典实现，但除非涉及到性能优化，我们一般不会关注这方面的事情，而且将来也可能会改变这种方式。命名空间的例子有：内置名称集合（包括 :func:`abs`"
" "
"函数以及内置异常的名称等）；一个模块的全局名称；一个函数调用中的局部名称。对象的属性集合也是命名空间的一种形式。关于命名空间的一个重要知识点是，不同命名空间中的名称之间绝对没有关系；例如，两个不同的模块都可以定义"
" ``maximize`` 函数，且不会造成混淆。用户使用函数时必须要在函数名前面加上模块名。"

#: ../../tutorial/classes.rst:82
msgid ""
"By the way, I use the word *attribute* for any name following a dot --- for "
"example, in the expression ``z.real``, ``real`` is an attribute of the "
"object ``z``.  Strictly speaking, references to names in modules are "
"attribute references: in the expression ``modname.funcname``, ``modname`` is"
" a module object and ``funcname`` is an attribute of it.  In this case there"
" happens to be a straightforward mapping between the module's attributes and"
" the global names defined in the module: they share the same namespace!  "
"[#]_"
msgstr ""
"点号之后的名称是 **属性**。例如，表达式 ``z.real`` 中，``real`` 是对象 ``z`` "
"的属性。严格来说，对模块中名称的引用是属性引用：表达式 ``modname.funcname`` 中，``modname`` "
"是模块对象，``funcname`` 是模块的属性。模块属性和模块中定义的全局名称之间存在直接的映射：它们共享相同的命名空间！ [#]_"

#: ../../tutorial/classes.rst:90
msgid ""
"Attributes may be read-only or writable.  In the latter case, assignment to "
"attributes is possible.  Module attributes are writable: you can write "
"``modname.the_answer = 42``.  Writable attributes may also be deleted with "
"the :keyword:`del` statement.  For example, ``del modname.the_answer`` will "
"remove the attribute :attr:`!the_answer` from the object named by "
"``modname``."
msgstr ""
"属性可以是只读的或者可写的。 在后一种情况下，可以对属性进行赋值。 模块属性是可写的：你可以写入 ``modname.the_answer = 42``"
" 。  也可以使用 :keyword:`del` 语句删除可写属性。 例如，``del modname.the_answer`` 将从名为 "
"``modname`` 对象中移除属性 :attr:`!the_answer`。"

#: ../../tutorial/classes.rst:96
msgid ""
"Namespaces are created at different moments and have different lifetimes.  "
"The namespace containing the built-in names is created when the Python "
"interpreter starts up, and is never deleted.  The global namespace for a "
"module is created when the module definition is read in; normally, module "
"namespaces also last until the interpreter quits.  The statements executed "
"by the top-level invocation of the interpreter, either read from a script "
"file or interactively, are considered part of a module called "
":mod:`__main__`, so they have their own global namespace.  (The built-in "
"names actually also live in a module; this is called :mod:`builtins`.)"
msgstr ""
"命名空间是在不同时刻创建的，且拥有不同的生命周期。内置名称的命名空间是在 Python "
"解释器启动时创建的，永远不会被删除。模块的全局命名空间在读取模块定义时创建；通常，模块的命名空间也会持续到解释器退出。从脚本文件读取或交互式读取的，由解释器顶层调用执行的语句是"
" :mod:`__main__` 模块调用的一部分，也拥有自己的全局命名空间。内置名称实际上也在模块里，即 :mod:`builtins` 。"

#: ../../tutorial/classes.rst:106
msgid ""
"The local namespace for a function is created when the function is called, "
"and deleted when the function returns or raises an exception that is not "
"handled within the function.  (Actually, forgetting would be a better way to"
" describe what actually happens.)  Of course, recursive invocations each "
"have their own local namespace."
msgstr ""
"函数的局部命名空间在函数被调用时被创建，并在函数返回或抛出未在函数内被处理的异常时，被删除。（实际上，用“遗忘”来描述实际发生的情况会更好一些。）当然，每次递归调用都有自己的局部命名空间。"

#: ../../tutorial/classes.rst:112
msgid ""
"A *scope* is a textual region of a Python program where a namespace is "
"directly accessible.  \"Directly accessible\" here means that an unqualified"
" reference to a name attempts to find the name in the namespace."
msgstr ""
"一个命名空间的 *作用域* 是 Python "
"代码中的一段文本区域，从这个区域可直接访问该命名空间。“可直接访问”的意思是，该文本区域内的名称在被非限定引用时，查找名称的范围，是包括该命名空间在内的。"

#: ../../tutorial/classes.rst:116
msgid ""
"Although scopes are determined statically, they are used dynamically. At any"
" time during execution, there are 3 or 4 nested scopes whose namespaces are "
"directly accessible:"
msgstr "作用域虽然是被静态确定的，但会被动态使用。执行期间的任何时刻，都会有 3 或 4 个“命名空间可直接访问”的嵌套作用域："

#: ../../tutorial/classes.rst:120
msgid "the innermost scope, which is searched first, contains the local names"
msgstr "最内层作用域，包含局部名称，并首先在其中进行搜索"

#: ../../tutorial/classes.rst:121
msgid ""
"the scopes of any enclosing functions, which are searched starting with the "
"nearest enclosing scope, contain non-local, but also non-global names"
msgstr "那些外层闭包函数的作用域，包含“非局部、非全局”的名称，从最靠内层的那个作用域开始，逐层向外搜索。"

#: ../../tutorial/classes.rst:123
msgid "the next-to-last scope contains the current module's global names"
msgstr "倒数第二层作用域，包含当前模块的全局名称"

#: ../../tutorial/classes.rst:124
msgid ""
"the outermost scope (searched last) is the namespace containing built-in "
"names"
msgstr "最外层（最后搜索）的作用域，是内置名称的命名空间"

#: ../../tutorial/classes.rst:126
msgid ""
"If a name is declared global, then all references and assignments go "
"directly to the next-to-last scope containing the module's global names.  To"
" rebind variables found outside of the innermost scope, the "
":keyword:`nonlocal` statement can be used; if not declared nonlocal, those "
"variables are read-only (an attempt to write to such a variable will simply "
"create a *new* local variable in the innermost scope, leaving the "
"identically named outer variable unchanged)."
msgstr ""
"如果一个名称被声明为全局，则所有引用和赋值都将直接指向“倒数第二层作用域”，即包含模块的全局名称的作用域。 "
"要重新绑定在最内层作用域以外找到的变量，可以使用 :keyword:`nonlocal` 语句；如果未使用 nonlocal "
"声明，这些变量将为只读（尝试写入这样的变量将在最内层作用域中创建一个 *新的* 局部变量，而使得同名的外部变量保持不变）。"

#: ../../tutorial/classes.rst:133
msgid ""
"Usually, the local scope references the local names of the (textually) "
"current function.  Outside functions, the local scope references the same "
"namespace as the global scope: the module's namespace. Class definitions "
"place yet another namespace in the local scope."
msgstr ""
"通常，当前局部作用域将（按字面文本）引用当前函数的局部名称。在函数之外，局部作用域引用与全局作用域一致的命名空间：模块的命名空间。 "
"类定义在局部命名空间内再放置另一个命名空间。"

#: ../../tutorial/classes.rst:138
msgid ""
"It is important to realize that scopes are determined textually: the global "
"scope of a function defined in a module is that module's namespace, no "
"matter from where or by what alias the function is called.  On the other "
"hand, the actual search for names is done dynamically, at run time --- "
"however, the language definition is evolving towards static name resolution,"
" at \"compile\" time, so don't rely on dynamic name resolution!  (In fact, "
"local variables are already determined statically.)"
msgstr ""
"划重点，作用域是按字面文本确定的：模块内定义的函数的全局作用域就是该模块的命名空间，无论该函数从什么地方或以什么别名被调用。另一方面，实际的名称搜索是在运行时动态完成的。但是，Python"
" 正在朝着“编译时静态名称解析”的方向发展，因此不要过于依赖动态名称解析！（局部变量已经是被静态确定了。）"

#: ../../tutorial/classes.rst:146
msgid ""
"A special quirk of Python is that -- if no :keyword:`global` or "
":keyword:`nonlocal` statement is in effect -- assignments to names always go"
" into the innermost scope. Assignments do not copy data --- they just bind "
"names to objects.  The same is true for deletions: the statement ``del x`` "
"removes the binding of ``x`` from the namespace referenced by the local "
"scope.  In fact, all operations that introduce new names use the local "
"scope: in particular, :keyword:`import` statements and function definitions "
"bind the module or function name in the local scope."
msgstr ""
"Python 有一个特殊规定。如果不存在生效的 :keyword:`global` 或 :keyword:`nonlocal` "
"语句，则对名称的赋值总是会进入最内层作用域。赋值不会复制数据，只是将名称绑定到对象。删除也是如此：语句 ``del x`` "
"从局部作用域引用的命名空间中移除对 ``x`` 的绑定。所有引入新名称的操作都是使用局部作用域：尤其是 :keyword:`import` "
"语句和函数定义会在局部作用域中绑定模块或函数名称。"

#: ../../tutorial/classes.rst:154
msgid ""
"The :keyword:`global` statement can be used to indicate that particular "
"variables live in the global scope and should be rebound there; the "
":keyword:`nonlocal` statement indicates that particular variables live in an"
" enclosing scope and should be rebound there."
msgstr ""
":keyword:`global` 语句用于表明特定变量在全局作用域里，并应在全局作用域中重新绑定；:keyword:`nonlocal` "
"语句表明特定变量在外层作用域中，并应在外层作用域中重新绑定。"

#: ../../tutorial/classes.rst:162
msgid "Scopes and Namespaces Example"
msgstr "作用域和命名空间示例"

#: ../../tutorial/classes.rst:164
msgid ""
"This is an example demonstrating how to reference the different scopes and "
"namespaces, and how :keyword:`global` and :keyword:`nonlocal` affect "
"variable binding::"
msgstr ""
"下例演示了如何引用不同作用域和名称空间，以及 :keyword:`global` 和 :keyword:`nonlocal` 对变量绑定的影响："

#: ../../tutorial/classes.rst:168
msgid ""
"def scope_test():\n"
"    def do_local():\n"
"        spam = \"local spam\"\n"
"\n"
"    def do_nonlocal():\n"
"        nonlocal spam\n"
"        spam = \"nonlocal spam\"\n"
"\n"
"    def do_global():\n"
"        global spam\n"
"        spam = \"global spam\"\n"
"\n"
"    spam = \"test spam\"\n"
"    do_local()\n"
"    print(\"After local assignment:\", spam)\n"
"    do_nonlocal()\n"
"    print(\"After nonlocal assignment:\", spam)\n"
"    do_global()\n"
"    print(\"After global assignment:\", spam)\n"
"\n"
"scope_test()\n"
"print(\"In global scope:\", spam)"
msgstr ""
"def scope_test():\n"
"    def do_local():\n"
"        spam = \"local spam\"\n"
"\n"
"    def do_nonlocal():\n"
"        nonlocal spam\n"
"        spam = \"nonlocal spam\"\n"
"\n"
"    def do_global():\n"
"        global spam\n"
"        spam = \"global spam\"\n"
"\n"
"    spam = \"test spam\"\n"
"    do_local()\n"
"    print(\"After local assignment:\", spam)\n"
"    do_nonlocal()\n"
"    print(\"After nonlocal assignment:\", spam)\n"
"    do_global()\n"
"    print(\"After global assignment:\", spam)\n"
"\n"
"scope_test()\n"
"print(\"In global scope:\", spam)"

#: ../../tutorial/classes.rst:191
msgid "The output of the example code is:"
msgstr "示例代码的输出是："

#: ../../tutorial/classes.rst:193
msgid ""
"After local assignment: test spam\n"
"After nonlocal assignment: nonlocal spam\n"
"After global assignment: nonlocal spam\n"
"In global scope: global spam"
msgstr ""
"After local assignment: test spam\n"
"After nonlocal assignment: nonlocal spam\n"
"After global assignment: nonlocal spam\n"
"In global scope: global spam"

#: ../../tutorial/classes.rst:200
msgid ""
"Note how the *local* assignment (which is default) didn't change "
"*scope_test*\\'s binding of *spam*.  The :keyword:`nonlocal` assignment "
"changed *scope_test*\\'s binding of *spam*, and the :keyword:`global` "
"assignment changed the module-level binding."
msgstr ""
"注意，**局部** 赋值（这是默认状态）不会改变 *scope_test* 对 *spam* 的绑定。 :keyword:`nonlocal` "
"赋值会改变 *scope_test* 对 *spam* 的绑定，而 :keyword:`global` 赋值会改变模块层级的绑定。"

#: ../../tutorial/classes.rst:205
msgid ""
"You can also see that there was no previous binding for *spam* before the "
":keyword:`global` assignment."
msgstr "而且，:keyword:`global` 赋值前没有 *spam* 的绑定。"

#: ../../tutorial/classes.rst:212
msgid "A First Look at Classes"
msgstr "初探类"

#: ../../tutorial/classes.rst:214
msgid ""
"Classes introduce a little bit of new syntax, three new object types, and "
"some new semantics."
msgstr "类引入了一点新语法，三种新的对象类型和一些新语义。"

#: ../../tutorial/classes.rst:221
msgid "Class Definition Syntax"
msgstr "类定义语法"

#: ../../tutorial/classes.rst:223
msgid "The simplest form of class definition looks like this::"
msgstr "最简单的类定义形式如下："

#: ../../tutorial/classes.rst:225
msgid ""
"class ClassName:\n"
"    <statement-1>\n"
"    .\n"
"    .\n"
"    .\n"
"    <statement-N>"
msgstr ""
"class ClassName:\n"
"    <语句-1>\n"
"    .\n"
"    .\n"
"    .\n"
"    <语句-N>"

#: ../../tutorial/classes.rst:232
msgid ""
"Class definitions, like function definitions (:keyword:`def` statements) "
"must be executed before they have any effect.  (You could conceivably place "
"a class definition in a branch of an :keyword:`if` statement, or inside a "
"function.)"
msgstr ""
"与函数定义 (:keyword:`def` 语句) 一样，类定义必须先执行才能生效。把类定义放在 :keyword:`if` "
"语句的分支里或函数内部试试。"

#: ../../tutorial/classes.rst:236
msgid ""
"In practice, the statements inside a class definition will usually be "
"function definitions, but other statements are allowed, and sometimes useful"
" --- we'll come back to this later.  The function definitions inside a class"
" normally have a peculiar form of argument list, dictated by the calling "
"conventions for methods --- again, this is explained later."
msgstr ""
"在实践中，类定义内的语句通常都是函数定义，但也可以是其他语句。这部分内容稍后再讨论。类里的函数定义一般是特殊的参数列表，这是由方法调用的约定规范所指明的"
" --- 同样，稍后再解释。"

#: ../../tutorial/classes.rst:242
msgid ""
"When a class definition is entered, a new namespace is created, and used as "
"the local scope --- thus, all assignments to local variables go into this "
"new namespace.  In particular, function definitions bind the name of the new"
" function here."
msgstr ""
"当进入类定义时，将创建一个新的命名空间，并将其用作局部作用域 --- 因此，所有对局部变量的赋值都是在这个新命名空间之内。 "
"特别的，函数定义会绑定到这里的新函数名称。"

#: ../../tutorial/classes.rst:247
msgid ""
"When a class definition is left normally (via the end), a *class object* is "
"created.  This is basically a wrapper around the contents of the namespace "
"created by the class definition; we'll learn more about class objects in the"
" next section.  The original local scope (the one in effect just before the "
"class definition was entered) is reinstated, and the class object is bound "
"here to the class name given in the class definition header "
"(:class:`!ClassName` in the example)."
msgstr ""
"当 (从结尾处) 正常离开类定义时，将创建一个 *类对象*。 "
"这基本上是一个围绕类定义所创建的命名空间的包装器；我们将在下一节中了解有关类对象的更多信息。 原始的 (在进入类定义之前有效的) "
"作用域将重新生效，类对象将在这里与类定义头所给出的类名称进行绑定 (在这个示例中为 :class:`!ClassName`)。"

#: ../../tutorial/classes.rst:259
msgid "Class Objects"
msgstr "Class 对象"

#: ../../tutorial/classes.rst:261
msgid ""
"Class objects support two kinds of operations: attribute references and "
"instantiation."
msgstr "类对象支持两种操作：属性引用和实例化。"

#: ../../tutorial/classes.rst:264
msgid ""
"*Attribute references* use the standard syntax used for all attribute "
"references in Python: ``obj.name``.  Valid attribute names are all the names"
" that were in the class's namespace when the class object was created.  So, "
"if the class definition looked like this::"
msgstr ""
"*属性引用* 使用 Python 中所有属性引用所使用的标准语法: ``obj.name``。 "
"有效的属性名称是类对象被创建时存在于类命名空间中的所有名称。 因此，如果类定义是这样的::"

#: ../../tutorial/classes.rst:269
msgid ""
"class MyClass:\n"
"    \"\"\"A simple example class\"\"\"\n"
"    i = 12345\n"
"\n"
"    def f(self):\n"
"        return 'hello world'"
msgstr ""
"class MyClass:\n"
"    \"\"\"一个简单的示例类\"\"\"\n"
"    i = 12345\n"
"\n"
"    def f(self):\n"
"        return 'hello world'"

#: ../../tutorial/classes.rst:276
msgid ""
"then ``MyClass.i`` and ``MyClass.f`` are valid attribute references, "
"returning an integer and a function object, respectively. Class attributes "
"can also be assigned to, so you can change the value of ``MyClass.i`` by "
"assignment. :attr:`~type.__doc__` is also a valid attribute, returning the "
"docstring belonging to the class: ``\"A simple example class\"``."
msgstr ""
"那么 ``MyClass.i`` 和 ``MyClass.f`` 就是有效的属性引用，将分别返回一个整数和一个函数对象。 "
"类属性也可以被赋值，因此可以通过赋值来改变 ``MyClass.i`` 的值。 :attr:`~type.__doc__` "
"也是一个有效的属性，将返回所属类的文档字符串: ``\"A simple example class\"``。"

#: ../../tutorial/classes.rst:282
msgid ""
"Class *instantiation* uses function notation.  Just pretend that the class "
"object is a parameterless function that returns a new instance of the class."
" For example (assuming the above class)::"
msgstr "类的 *实例化* 使用函数表示法。 可以把类对象视为是返回该类的一个新实例的不带参数的函数。 举例来说（假设使用上述的类）::"

#: ../../tutorial/classes.rst:286 ../../tutorial/classes.rst:303
msgid "x = MyClass()"
msgstr "x = MyClass()"

#: ../../tutorial/classes.rst:288
msgid ""
"creates a new *instance* of the class and assigns this object to the local "
"variable ``x``."
msgstr "创建类的新 *实例* 并将此对象分配给局部变量 ``x``。"

#: ../../tutorial/classes.rst:291
msgid ""
"The instantiation operation (\"calling\" a class object) creates an empty "
"object. Many classes like to create objects with instances customized to a "
"specific initial state. Therefore a class may define a special method named "
":meth:`~object.__init__`, like this::"
msgstr ""
"实例化操作 (“调用”类对象) 会创建一个空对象。 许多类都希望创建的对象实例是根据特定初始状态定制的。 因此一个类可能会定义名为 "
":meth:`~object.__init__` 的特殊方法，就像这样::"

#: ../../tutorial/classes.rst:296
msgid ""
"def __init__(self):\n"
"    self.data = []"
msgstr ""
"def __init__(self):\n"
"    self.data = []"

#: ../../tutorial/classes.rst:299
msgid ""
"When a class defines an :meth:`~object.__init__` method, class instantiation"
" automatically invokes :meth:`!__init__` for the newly created class "
"instance.  So in this example, a new, initialized instance can be obtained "
"by::"
msgstr ""
"当一个类定义了 :meth:`~object.__init__` 方法时，类的实例化会自动为新创建的类实例唤起 :meth:`!__init__`。 "
"因此在这个例子中，可以通过以下语句获得一个已初始化的新实例::"

#: ../../tutorial/classes.rst:305
msgid ""
"Of course, the :meth:`~object.__init__` method may have arguments for "
"greater flexibility.  In that case, arguments given to the class "
"instantiation operator are passed on to :meth:`!__init__`.  For example, ::"
msgstr ""
"当然，:meth:`~object.__init__` 方法还有一些参数用于实现更高的灵活性。 在这种情况下，提供给类实例化运算符的参数将被传递给 "
":meth:`!__init__`。 例如， ::"

#: ../../tutorial/classes.rst:309
msgid ""
">>> class Complex:\n"
"...     def __init__(self, realpart, imagpart):\n"
"...         self.r = realpart\n"
"...         self.i = imagpart\n"
"...\n"
">>> x = Complex(3.0, -4.5)\n"
">>> x.r, x.i\n"
"(3.0, -4.5)"
msgstr ""
">>> class Complex:\n"
"...     def __init__(self, realpart, imagpart):\n"
"...         self.r = realpart\n"
"...         self.i = imagpart\n"
"...\n"
">>> x = Complex(3.0, -4.5)\n"
">>> x.r, x.i\n"
"(3.0, -4.5)"

#: ../../tutorial/classes.rst:322
msgid "Instance Objects"
msgstr "实例对象"

#: ../../tutorial/classes.rst:324
msgid ""
"Now what can we do with instance objects?  The only operations understood by"
" instance objects are attribute references.  There are two kinds of valid "
"attribute names: data attributes and methods."
msgstr "现在我们能用实例对象做什么？ 实例对象所能理解的唯一操作是属性引用。 有两种有效的属性名称：数据属性和方法。"

#: ../../tutorial/classes.rst:328
msgid ""
"*data attributes* correspond to \"instance variables\" in Smalltalk, and to "
"\"data members\" in C++.  Data attributes need not be declared; like local "
"variables, they spring into existence when they are first assigned to.  For "
"example, if ``x`` is the instance of :class:`!MyClass` created above, the "
"following piece of code will print the value ``16``, without leaving a "
"trace::"
msgstr ""
"*数据属性* 对应于 Smalltalk 中的“实例变量”，以及 C++ 中的“数据成员”。 "
"数据属性不需要声明；就像局部变量一样，它们将在首次被赋值时产生。 举例来说，如果 ``x`` 是上面创建的 :class:`!MyClass` "
"的实例，则以下代码将打印数值 ``16``，且不保留任何追踪信息::"

#: ../../tutorial/classes.rst:334
msgid ""
"x.counter = 1\n"
"while x.counter < 10:\n"
"    x.counter = x.counter * 2\n"
"print(x.counter)\n"
"del x.counter"
msgstr ""
"x.counter = 1\n"
"while x.counter < 10:\n"
"    x.counter = x.counter * 2\n"
"print(x.counter)\n"
"del x.counter"

#: ../../tutorial/classes.rst:340
msgid ""
"The other kind of instance attribute reference is a *method*. A method is a "
"function that \"belongs to\" an object."
msgstr "另一种实例属性引用称为 *方法*。 方法是“从属于”对象的函数。"

#: ../../tutorial/classes.rst:345
msgid ""
"Valid method names of an instance object depend on its class.  By "
"definition, all attributes of a class that are function  objects define "
"corresponding methods of its instances.  So in our example, ``x.f`` is a "
"valid method reference, since ``MyClass.f`` is a function, but ``x.i`` is "
"not, since ``MyClass.i`` is not.  But ``x.f`` is not the same thing as "
"``MyClass.f`` --- it is a *method object*, not a function object."
msgstr ""
"实例对象的有效方法名称依赖于其所属的类。 根据定义，一个类中所有是函数对象的属性都是定义了其实例的相应方法。 因此在我们的示例中，``x.f`` "
"是有效的方法引用，因为 ``MyClass.f`` 是一个函数，而 ``x.i`` 不是方法，因为 ``MyClass.i`` 不是函数。 但是 "
"``x.f`` 与 ``MyClass.f`` 并不是一回事 --- 它是一个 *方法对象*，不是函数对象。"

#: ../../tutorial/classes.rst:356
msgid "Method Objects"
msgstr "方法对象"

#: ../../tutorial/classes.rst:358
msgid "Usually, a method is called right after it is bound::"
msgstr "通常，方法在绑定后立即被调用::"

#: ../../tutorial/classes.rst:360
msgid "x.f()"
msgstr "x.f()"

#: ../../tutorial/classes.rst:362
msgid ""
"In the :class:`!MyClass` example, this will return the string ``'hello "
"world'``. However, it is not necessary to call a method right away: ``x.f`` "
"is a method object, and can be stored away and called at a later time.  For "
"example::"
msgstr ""
"在 :class:`!MyClass` 示例中，这将返回字符串 ``'hello world'``。 但是，方法并不是必须立即调用: ``x.f`` "
"是一个方法对象，它可以被保存起来以后再调用。 例如::"

#: ../../tutorial/classes.rst:366
msgid ""
"xf = x.f\n"
"while True:\n"
"    print(xf())"
msgstr ""
"xf = x.f\n"
"while True:\n"
"    print(xf())"

#: ../../tutorial/classes.rst:370
msgid "will continue to print ``hello world`` until the end of time."
msgstr "将持续打印 ``hello world``，直到结束。"

#: ../../tutorial/classes.rst:372
msgid ""
"What exactly happens when a method is called?  You may have noticed that "
"``x.f()`` was called without an argument above, even though the function "
"definition for :meth:`!f` specified an argument.  What happened to the "
"argument? Surely Python raises an exception when a function that requires an"
" argument is called without any --- even if the argument isn't actually "
"used..."
msgstr ""
"当一个方法被调用时究竟会发生什么？ 你可能已经注意到尽管 :meth:`!f` 的函数定义指定了一个参数，但上面调用 ``x.f()`` "
"时却没有带参数。 这个参数发生了什么事？ 当一个需要参数的函数在不附带任何参数的情况下被调用时 Python 肯定会引发异常 --- "
"即使参数实际上没有被使用..."

#: ../../tutorial/classes.rst:378
msgid ""
"Actually, you may have guessed the answer: the special thing about methods "
"is that the instance object is passed as the first argument of the function."
"  In our example, the call ``x.f()`` is exactly equivalent to "
"``MyClass.f(x)``.  In general, calling a method with a list of *n* arguments"
" is equivalent to calling the corresponding function with an argument list "
"that is created by inserting the method's instance object before the first "
"argument."
msgstr ""
"实际上，你可能已经猜到了答案：方法的特殊之处就在于实例对象会作为函数的第一个参数被传入。 在我们的示例中，调用 ``x.f()`` 其实就相当于 "
"``MyClass.f(x)``。 总之，调用一个具有 *n* "
"个参数的方法就相当于调用再多一个参数的对应函数，这个参数值为方法所属实例对象，位置在其他参数之前。"

#: ../../tutorial/classes.rst:385
msgid ""
"In general, methods work as follows.  When a non-data attribute of an "
"instance is referenced, the instance's class is searched. If the name "
"denotes a valid class attribute that is a function object, references to "
"both the instance object and the function object are packed into a method "
"object.  When the method object is called with an argument list, a new "
"argument list is constructed from the instance object and the argument list,"
" and the function object is called with this new argument list."
msgstr ""
"总而言之，方法的运作方式如下。 当一个实例的非数据属性被引用时，将搜索该实例所属的类。 "
"如果名称表示一个属于函数对象的有效类属性，则指向实例对象和函数对象的引用将被打包为一个方法对象。 "
"当传入一个参数列表调用该方法对象时，将基于实例对象和参数列表构造一个新的参数列表，并传入这个新参数列表调用相应的函数对象。"

#: ../../tutorial/classes.rst:398
msgid "Class and Instance Variables"
msgstr "类和实例变量"

#: ../../tutorial/classes.rst:400
msgid ""
"Generally speaking, instance variables are for data unique to each instance "
"and class variables are for attributes and methods shared by all instances "
"of the class::"
msgstr "一般来说，实例变量用于每个实例的唯一数据，而类变量用于类的所有实例共享的属性和方法::"

#: ../../tutorial/classes.rst:404
msgid ""
"class Dog:\n"
"\n"
"    kind = 'canine'         # class variable shared by all instances\n"
"\n"
"    def __init__(self, name):\n"
"        self.name = name    # instance variable unique to each instance\n"
"\n"
">>> d = Dog('Fido')\n"
">>> e = Dog('Buddy')\n"
">>> d.kind                  # shared by all dogs\n"
"'canine'\n"
">>> e.kind                  # shared by all dogs\n"
"'canine'\n"
">>> d.name                  # unique to d\n"
"'Fido'\n"
">>> e.name                  # unique to e\n"
"'Buddy'"
msgstr ""
"class Dog:\n"
"\n"
"    kind = 'canine'         # 类变量被所有实例所共享\n"
"\n"
"    def __init__(self, name):\n"
"        self.name = name    # 实例变量为每个实例所独有\n"
"\n"
">>> d = Dog('Fido')\n"
">>> e = Dog('Buddy')\n"
">>> d.kind                  # 被所有的 Dog 实例所共享\n"
"'canine'\n"
">>> e.kind                  # 被所有的 Dog 实例所共享\n"
"'canine'\n"
">>> d.name                  # 为 d 所独有\n"
"'Fido'\n"
">>> e.name                  # 为 e 所独有\n"
"'Buddy'"

#: ../../tutorial/classes.rst:422
msgid ""
"As discussed in :ref:`tut-object`, shared data can have possibly surprising "
"effects with involving :term:`mutable` objects such as lists and "
"dictionaries. For example, the *tricks* list in the following code should "
"not be used as a class variable because just a single list would be shared "
"by all *Dog* instances::"
msgstr ""
"正如 :ref:`tut-object` 中已讨论过的，共享数据可能在涉及 :term:`mutable` 对象例如列表和字典的时候导致令人惊讶的结果。"
" 例如以下代码中的 *tricks* 列表不应该被用作类变量，因为所有的 *Dog* 实例将只共享一个单独的列表::"

#: ../../tutorial/classes.rst:428
msgid ""
"class Dog:\n"
"\n"
"    tricks = []             # mistaken use of a class variable\n"
"\n"
"    def __init__(self, name):\n"
"        self.name = name\n"
"\n"
"    def add_trick(self, trick):\n"
"        self.tricks.append(trick)\n"
"\n"
">>> d = Dog('Fido')\n"
">>> e = Dog('Buddy')\n"
">>> d.add_trick('roll over')\n"
">>> e.add_trick('play dead')\n"
">>> d.tricks                # unexpectedly shared by all dogs\n"
"['roll over', 'play dead']"
msgstr ""
"class Dog:\n"
"\n"
"    tricks = []             # 类变量的错误用法\n"
"\n"
"    def __init__(self, name):\n"
"        self.name = name\n"
"\n"
"    def add_trick(self, trick):\n"
"        self.tricks.append(trick)\n"
"\n"
">>> d = Dog('Fido')\n"
">>> e = Dog('Buddy')\n"
">>> d.add_trick('roll over')\n"
">>> e.add_trick('play dead')\n"
">>> d.tricks                # 非预期地被所有的 Dog 实例所共享\n"
"['roll over', 'play dead']"

#: ../../tutorial/classes.rst:445
msgid "Correct design of the class should use an instance variable instead::"
msgstr "正确的类设计应该使用实例变量::"

#: ../../tutorial/classes.rst:447
msgid ""
"class Dog:\n"
"\n"
"    def __init__(self, name):\n"
"        self.name = name\n"
"        self.tricks = []    # creates a new empty list for each dog\n"
"\n"
"    def add_trick(self, trick):\n"
"        self.tricks.append(trick)\n"
"\n"
">>> d = Dog('Fido')\n"
">>> e = Dog('Buddy')\n"
">>> d.add_trick('roll over')\n"
">>> e.add_trick('play dead')\n"
">>> d.tricks\n"
"['roll over']\n"
">>> e.tricks\n"
"['play dead']"
msgstr ""
"class Dog:\n"
"\n"
"    def __init__(self, name):\n"
"        self.name = name\n"
"        self.tricks = []    # 为每个 Dog 实例新建一个空列表\n"
"\n"
"    def add_trick(self, trick):\n"
"        self.tricks.append(trick)\n"
"\n"
">>> d = Dog('Fido')\n"
">>> e = Dog('Buddy')\n"
">>> d.add_trick('roll over')\n"
">>> e.add_trick('play dead')\n"
">>> d.tricks\n"
"['roll over']\n"
">>> e.tricks\n"
"['play dead']"

#: ../../tutorial/classes.rst:469
msgid "Random Remarks"
msgstr "补充说明"

#: ../../tutorial/classes.rst:473
msgid ""
"If the same attribute name occurs in both an instance and in a class, then "
"attribute lookup prioritizes the instance::"
msgstr "如果同样的属性名称同时出现在实例和类中，则属性查找会优先选择实例::"

#: ../../tutorial/classes.rst:476
msgid ""
">>> class Warehouse:\n"
"...    purpose = 'storage'\n"
"...    region = 'west'\n"
"...\n"
">>> w1 = Warehouse()\n"
">>> print(w1.purpose, w1.region)\n"
"storage west\n"
">>> w2 = Warehouse()\n"
">>> w2.region = 'east'\n"
">>> print(w2.purpose, w2.region)\n"
"storage east"
msgstr ""
">>> class Warehouse:\n"
"...    purpose = 'storage'\n"
"...    region = 'west'\n"
"...\n"
">>> w1 = Warehouse()\n"
">>> print(w1.purpose, w1.region)\n"
"storage west\n"
">>> w2 = Warehouse()\n"
">>> w2.region = 'east'\n"
">>> print(w2.purpose, w2.region)\n"
"storage east"

#: ../../tutorial/classes.rst:488
msgid ""
"Data attributes may be referenced by methods as well as by ordinary users "
"(\"clients\") of an object.  In other words, classes are not usable to "
"implement pure abstract data types.  In fact, nothing in Python makes it "
"possible to enforce data hiding --- it is all based upon convention.  (On "
"the other hand, the Python implementation, written in C, can completely hide"
" implementation details and control access to an object if necessary; this "
"can be used by extensions to Python written in C.)"
msgstr ""
"数据属性可以被方法以及一个对象的普通用户（“客户端”）所引用。 换句话说，类不能用于实现纯抽象数据类型。 实际上，在 Python "
"中没有任何东西能强制隐藏数据 --- 它是完全基于约定的。 （而在另一方面，用 C 语言编写的 Python "
"实现则可以完全隐藏实现细节，并在必要时控制对象的访问；此特性可以通过用 C 编写 Python 扩展来使用。）"

#: ../../tutorial/classes.rst:496
msgid ""
"Clients should use data attributes with care --- clients may mess up "
"invariants maintained by the methods by stamping on their data attributes.  "
"Note that clients may add data attributes of their own to an instance object"
" without affecting the validity of the methods, as long as name conflicts "
"are avoided --- again, a naming convention can save a lot of headaches here."
msgstr ""
"客户端应当谨慎地使用数据属性 --- 客户端可能通过直接操作数据属性的方式破坏由方法所维护的固定变量。 "
"请注意客户端可以向一个实例对象添加他们自己的数据属性而不会影响方法的可用性，只要保证避免名称冲突 --- "
"再次提醒，在此使用命名约定可以省去许多令人头痛的麻烦。"

#: ../../tutorial/classes.rst:502
msgid ""
"There is no shorthand for referencing data attributes (or other methods!) "
"from within methods.  I find that this actually increases the readability of"
" methods: there is no chance of confusing local variables and instance "
"variables when glancing through a method."
msgstr ""
"在方法内部引用数据属性（或其他方法！）并没有简便方式。 我发现这实际上提升了方法的可读性：当浏览一个方法代码时，不会存在混淆局部变量和实例变量的机会。"

#: ../../tutorial/classes.rst:507
msgid ""
"Often, the first argument of a method is called ``self``.  This is nothing "
"more than a convention: the name ``self`` has absolutely no special meaning "
"to Python.  Note, however, that by not following the convention your code "
"may be less readable to other Python programmers, and it is also conceivable"
" that a *class browser* program might be written that relies upon such a "
"convention."
msgstr ""
"方法的第一个参数常常被命名为 ``self``。 这也不过就是一个约定: ``self`` 这一名称在 Python 中绝对没有特殊含义。 "
"但是要注意，不遵循此约定会使得你的代码对其他 Python 程序员来说缺乏可读性，而且也可以想像一个 *类浏览器* 程序的编写可能会依赖于这样的约定。"

#: ../../tutorial/classes.rst:513
msgid ""
"Any function object that is a class attribute defines a method for instances"
" of that class.  It is not necessary that the function definition is "
"textually enclosed in the class definition: assigning a function object to a"
" local variable in the class is also ok.  For example::"
msgstr ""
"任何一个作为类属性的函数都为该类的实例定义了一个相应方法。 函数定义的文本并非必须包含于类定义之内：将一个函数对象赋值给一个局部变量也是可以的。 "
"例如::"

#: ../../tutorial/classes.rst:518
msgid ""
"# Function defined outside the class\n"
"def f1(self, x, y):\n"
"    return min(x, x+y)\n"
"\n"
"class C:\n"
"    f = f1\n"
"\n"
"    def g(self):\n"
"        return 'hello world'\n"
"\n"
"    h = g"
msgstr ""
"# 在类之外定义的函数\n"
"def f1(self, x, y):\n"
"    return min(x, x+y)\n"
"\n"
"class C:\n"
"    f = f1\n"
"\n"
"    def g(self):\n"
"        return 'hello world'\n"
"\n"
"    h = g"

#: ../../tutorial/classes.rst:530
msgid ""
"Now ``f``, ``g`` and ``h`` are all attributes of class :class:`!C` that "
"refer to function objects, and consequently they are all methods of "
"instances of :class:`!C` --- ``h`` being exactly equivalent to ``g``.  Note "
"that this practice usually only serves to confuse the reader of a program."
msgstr ""
"现在 ``f``、``g`` 和 ``h`` 都 :class:`!C` 类的指向函数对象的属性，因此它们都是 :class:`!C` 实例的方法 "
"--- 其中 ``h`` 与 ``g`` 完全等价。 但请注意这种做法通常只会使程序的阅读者感到迷惑。"

#: ../../tutorial/classes.rst:535
msgid ""
"Methods may call other methods by using method attributes of the ``self`` "