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# eric R <trencyclopedia@gmail.com>, 2020
# Woko <banbooliu@gmail.com>, 2020
# df2dc1c92e792f7ae8417c51df43db8f_594d92a <0f49be28017426edb1db1a2ab6e67088_717605>, 2020
# Freesand Leo <yuqinju@163.com>, 2020
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# 
#, fuzzy
msgid ""
msgstr ""
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"Plural-Forms: nplurals=1; plural=0;\n"

#: ../../tutorial/datastructures.rst:5
msgid "Data Structures"
msgstr "数据结构"

#: ../../tutorial/datastructures.rst:7
msgid ""
"This chapter describes some things you've learned about already in more "
"detail, and adds some new things as well."
msgstr "本章深入讲解之前学过的一些内容，同时，还增加了新的知识点。"

#: ../../tutorial/datastructures.rst:13
msgid "More on Lists"
msgstr "列表详解"

#: ../../tutorial/datastructures.rst:15
msgid ""
"The list data type has some more methods.  Here are all of the methods of "
"list objects:"
msgstr "列表数据类型支持很多方法，列表对象的所有方法所示如下："

#: ../../tutorial/datastructures.rst:22
msgid ""
"Add an item to the end of the list.  Equivalent to ``a[len(a):] = [x]``."
msgstr "在列表末尾添加一个元素，相当于 ``a[len(a):] = [x]`` 。"

#: ../../tutorial/datastructures.rst:28
msgid ""
"Extend the list by appending all the items from the iterable.  Equivalent to"
" ``a[len(a):] = iterable``."
msgstr "用可迭代对象的元素扩展列表。相当于  ``a[len(a):] = iterable`` 。"

#: ../../tutorial/datastructures.rst:35
msgid ""
"Insert an item at a given position.  The first argument is the index of the "
"element before which to insert, so ``a.insert(0, x)`` inserts at the front "
"of the list, and ``a.insert(len(a), x)`` is equivalent to ``a.append(x)``."
msgstr ""
"在指定位置插入元素。第一个参数是插入元素的索引，因此，``a.insert(0, x)`` 在列表开头插入元素， ``a.insert(len(a), "
"x)`` 等同于 ``a.append(x)`` 。"

#: ../../tutorial/datastructures.rst:43
msgid ""
"Remove the first item from the list whose value is equal to *x*.  It raises "
"a :exc:`ValueError` if there is no such item."
msgstr "从列表中删除第一个值为 *x* 的元素。未找到指定元素时，触发 :exc:`ValueError` 异常。"

#: ../../tutorial/datastructures.rst:50
msgid ""
"Remove the item at the given position in the list, and return it.  If no "
"index is specified, ``a.pop()`` removes and returns the last item in the "
"list.  (The square brackets around the *i* in the method signature denote "
"that the parameter is optional, not that you should type square brackets at "
"that position.  You will see this notation frequently in the Python Library "
"Reference.)"
msgstr ""
"删除列表中指定位置的元素，并返回被删除的元素。未指定位置时，``a.pop()`` 删除并返回列表的最后一个元素。（方法签名中 *i* "
"两边的方括号表示该参数是可选的，不是要求输入方括号。这种表示法常见于 Python 参考库）。"

#: ../../tutorial/datastructures.rst:60
msgid "Remove all items from the list.  Equivalent to ``del a[:]``."
msgstr "删除列表里的所有元素，相当于 ``del a[:]`` 。"

#: ../../tutorial/datastructures.rst:66
msgid ""
"Return zero-based index in the list of the first item whose value is equal "
"to *x*. Raises a :exc:`ValueError` if there is no such item."
msgstr "返回列表中第一个值为 *x* 的元素的零基索引。未找到指定元素时，触发 :exc:`ValueError` 异常。"

#: ../../tutorial/datastructures.rst:69
msgid ""
"The optional arguments *start* and *end* are interpreted as in the slice "
"notation and are used to limit the search to a particular subsequence of the"
" list.  The returned index is computed relative to the beginning of the full"
" sequence rather than the *start* argument."
msgstr ""
"可选参数 *start* 和 *end* 是切片符号，用于将搜索限制为列表的特定子序列。返回的索引是相对于整个序列的开始计算的，而不是 *start* "
"参数。"

#: ../../tutorial/datastructures.rst:78
msgid "Return the number of times *x* appears in the list."
msgstr "返回列表中元素 *x* 出现的次数。"

#: ../../tutorial/datastructures.rst:84
msgid ""
"Sort the items of the list in place (the arguments can be used for sort "
"customization, see :func:`sorted` for their explanation)."
msgstr "就地排序列表中的元素（要了解自定义排序参数，详见 :func:`sorted`）。"

#: ../../tutorial/datastructures.rst:91
msgid "Reverse the elements of the list in place."
msgstr "翻转列表中的元素。"

#: ../../tutorial/datastructures.rst:97
msgid "Return a shallow copy of the list.  Equivalent to ``a[:]``."
msgstr "返回列表的浅拷贝。相当于 ``a[:]``  。"

#: ../../tutorial/datastructures.rst:100
msgid "An example that uses most of the list methods::"
msgstr "多数列表方法示例："

#: ../../tutorial/datastructures.rst:123
msgid ""
"You might have noticed that methods like ``insert``, ``remove`` or ``sort`` "
"that only modify the list have no return value printed -- they return the "
"default ``None``. [1]_  This is a design principle for all mutable data "
"structures in Python."
msgstr ""
"``insert``、``remove``、``sort`` 等方法只修改列表，不输出返回值——返回的默认值为 ``None`` 。[1]_ 这是所有 "
"Python 可变数据结构的设计原则。"

#: ../../tutorial/datastructures.rst:128
msgid ""
"Another thing you might notice is that not all data can be sorted or "
"compared.  For instance, ``[None, 'hello', 10]`` doesn't sort because "
"integers can't be compared to strings and *None* can't be compared to other "
"types.  Also, there are some types that don't have a defined ordering "
"relation.  For example, ``3+4j < 5+7j`` isn't a valid comparison."
msgstr ""
"还有，不是所有数据都可以排序或比较。例如，``[None, 'hello', 10]`` 就不可排序，因为整数不能与字符串对比，而 *None* "
"不能与其他类型对比。有些类型根本就没有定义顺序关系，例如，``3+4j < 5+7j`` 这种对比操作就是无效的。"

#: ../../tutorial/datastructures.rst:139
msgid "Using Lists as Stacks"
msgstr "用列表实现堆栈"

#: ../../tutorial/datastructures.rst:144
msgid ""
"The list methods make it very easy to use a list as a stack, where the last "
"element added is the first element retrieved (\"last-in, first-out\").  To "
"add an item to the top of the stack, use :meth:`append`.  To retrieve an "
"item from the top of the stack, use :meth:`pop` without an explicit index.  "
"For example::"
msgstr ""
"使用列表方法实现堆栈非常容易，最后插入的最先取出（“后进先出”）。把元素添加到堆栈的顶端，使用 :meth:`append` 。从堆栈顶部取出元素，使用"
" :meth:`pop` ，不用指定索引。例如："

#: ../../tutorial/datastructures.rst:169
msgid "Using Lists as Queues"
msgstr "用列表实现队列"

#: ../../tutorial/datastructures.rst:173
msgid ""
"It is also possible to use a list as a queue, where the first element added "
"is the first element retrieved (\"first-in, first-out\"); however, lists are"
" not efficient for this purpose.  While appends and pops from the end of "
"list are fast, doing inserts or pops from the beginning of a list is slow "
"(because all of the other elements have to be shifted by one)."
msgstr ""
"列表也可以用作队列，最先加入的元素，最先取出（“先进先出”）；然而，列表作为队列的效率很低。因为，在列表末尾添加和删除元素非常快，但在列表开头插入或移除元素却很慢（因为所有其他元素都必须移动一位）。"

#: ../../tutorial/datastructures.rst:179
msgid ""
"To implement a queue, use :class:`collections.deque` which was designed to "
"have fast appends and pops from both ends.  For example::"
msgstr "实现队列最好用 :class:`collections.deque`，可以快速从两端添加或删除元素。例如："

#: ../../tutorial/datastructures.rst:197
msgid "List Comprehensions"
msgstr "列表推导式"

#: ../../tutorial/datastructures.rst:199
msgid ""
"List comprehensions provide a concise way to create lists. Common "
"applications are to make new lists where each element is the result of some "
"operations applied to each member of another sequence or iterable, or to "
"create a subsequence of those elements that satisfy a certain condition."
msgstr ""
"列表推导式创建列表的方式更简洁。常见的用法为，对序列或可迭代对象中的每个元素应用某种操作，用生成的结果创建新的列表；或用满足特定条件的元素创建子序列。"

#: ../../tutorial/datastructures.rst:204
msgid "For example, assume we want to create a list of squares, like::"
msgstr "例如，创建平方值的列表："

#: ../../tutorial/datastructures.rst:213
msgid ""
"Note that this creates (or overwrites) a variable named ``x`` that still "
"exists after the loop completes.  We can calculate the list of squares "
"without any side effects using::"
msgstr "注意，这段代码创建（或覆盖）变量 ``x``，该变量在循环结束后仍然存在。下述方法可以无副作用地计算平方列表："

#: ../../tutorial/datastructures.rst:219
msgid "or, equivalently::"
msgstr "或等价于："

#: ../../tutorial/datastructures.rst:223
msgid "which is more concise and readable."
msgstr "上面这种写法更简洁、易读。"

#: ../../tutorial/datastructures.rst:225
msgid ""
"A list comprehension consists of brackets containing an expression followed "
"by a :keyword:`!for` clause, then zero or more :keyword:`!for` or "
":keyword:`!if` clauses.  The result will be a new list resulting from "
"evaluating the expression in the context of the :keyword:`!for` and "
":keyword:`!if` clauses which follow it. For example, this listcomp combines "
"the elements of two lists if they are not equal::"
msgstr ""
"列表推导式的方括号内包含以下内容：一个表达式，后面为一个 :keyword:`!for` 子句，然后，是零个或多个 :keyword:`!for` 或 "
":keyword:`!if` 子句。结果是由表达式依据 :keyword:`!for` 和 :keyword:`!if` 子句求值计算而得出一个新列表。"
" 举例来说，以下列表推导式将两个列表中不相等的元素组合起来："

#: ../../tutorial/datastructures.rst:235
msgid "and it's equivalent to::"
msgstr "等价于："

#: ../../tutorial/datastructures.rst:246
msgid ""
"Note how the order of the :keyword:`for` and :keyword:`if` statements is the"
" same in both these snippets."
msgstr "注意，上面两段代码中，:keyword:`for` 和 :keyword:`if` 的顺序相同。"

#: ../../tutorial/datastructures.rst:249
msgid ""
"If the expression is a tuple (e.g. the ``(x, y)`` in the previous example), "
"it must be parenthesized. ::"
msgstr "表达式是元组（例如上例的 ``(x, y)``）时，必须加上括号："

#: ../../tutorial/datastructures.rst:280
msgid ""
"List comprehensions can contain complex expressions and nested functions::"
msgstr "列表推导式可以使用复杂的表达式和嵌套函数："

#: ../../tutorial/datastructures.rst:287
msgid "Nested List Comprehensions"
msgstr "嵌套的列表推导式"

#: ../../tutorial/datastructures.rst:289
msgid ""
"The initial expression in a list comprehension can be any arbitrary "
"expression, including another list comprehension."
msgstr "列表推导式中的初始表达式可以是任何表达式，甚至可以是另一个列表推导式。"

#: ../../tutorial/datastructures.rst:292
msgid ""
"Consider the following example of a 3x4 matrix implemented as a list of 3 "
"lists of length 4::"
msgstr "下面这个 3x4 矩阵，由 3 个长度为 4 的列表组成："

#: ../../tutorial/datastructures.rst:301
msgid "The following list comprehension will transpose rows and columns::"
msgstr "下面的列表推导式可以转置行列："

#: ../../tutorial/datastructures.rst:306
msgid ""
"As we saw in the previous section, the nested listcomp is evaluated in the "
"context of the :keyword:`for` that follows it, so this example is equivalent"
" to::"
msgstr "如上节所示，嵌套的列表推导式基于其后的 :keyword:`for` 求值，所以这个例子等价于："

#: ../../tutorial/datastructures.rst:317
msgid "which, in turn, is the same as::"
msgstr "反过来说，也等价于："

#: ../../tutorial/datastructures.rst:330
msgid ""
"In the real world, you should prefer built-in functions to complex flow "
"statements. The :func:`zip` function would do a great job for this use "
"case::"
msgstr "实际应用中，最好用内置函数替代复杂的流程语句。此时，:func:`zip` 函数更好用："

#: ../../tutorial/datastructures.rst:336
msgid ""
"See :ref:`tut-unpacking-arguments` for details on the asterisk in this line."
msgstr "关于本行中星号的详细说明，参见 :ref:`tut-unpacking-arguments`。"

#: ../../tutorial/datastructures.rst:341
msgid "The :keyword:`!del` statement"
msgstr ":keyword:`!del` 语句"

#: ../../tutorial/datastructures.rst:343
msgid ""
"There is a way to remove an item from a list given its index instead of its "
"value: the :keyword:`del` statement.  This differs from the :meth:`pop` "
"method which returns a value.  The :keyword:`!del` statement can also be "
"used to remove slices from a list or clear the entire list (which we did "
"earlier by assignment of an empty list to the slice).  For example::"
msgstr ""
":keyword:`del` 语句按索引，而不是值从列表中移除元素。与返回值的 :meth:`pop` 方法不同， :keyword:`!del` "
"语句也可以从列表中移除切片，或清空整个列表（之前是将空列表赋值给切片）。 例如："

#: ../../tutorial/datastructures.rst:360
msgid ":keyword:`del` can also be used to delete entire variables::"
msgstr ":keyword:`del` 也可以用来删除整个变量："

#: ../../tutorial/datastructures.rst:364
msgid ""
"Referencing the name ``a`` hereafter is an error (at least until another "
"value is assigned to it).  We'll find other uses for :keyword:`del` later."
msgstr "此后，再引用 ``a`` 就会报错（直到为它赋与另一个值）。后文会介绍 :keyword:`del` 的其他用法。"

#: ../../tutorial/datastructures.rst:371
msgid "Tuples and Sequences"
msgstr "元组和序列"

#: ../../tutorial/datastructures.rst:373
msgid ""
"We saw that lists and strings have many common properties, such as indexing "
"and slicing operations.  They are two examples of *sequence* data types (see"
" :ref:`typesseq`).  Since Python is an evolving language, other sequence "
"data types may be added.  There is also another standard sequence data type:"
" the *tuple*."
msgstr ""
"列表和字符串有很多共性，例如，索引和切片操作。这两种数据类型是 *序列* （参见 :ref:`typesseq`）。随着 Python "
"语言的发展，其他的序列类型也被加入其中。本节介绍另一种标准序列类型：*元组*。"

#: ../../tutorial/datastructures.rst:379
msgid ""
"A tuple consists of a number of values separated by commas, for instance::"
msgstr "元组由多个用逗号隔开的值组成，例如："

#: ../../tutorial/datastructures.rst:401
msgid ""
"As you see, on output tuples are always enclosed in parentheses, so that "
"nested tuples are interpreted correctly; they may be input with or without "
"surrounding parentheses, although often parentheses are necessary anyway (if"
" the tuple is part of a larger expression).  It is not possible to assign to"
" the individual items of a tuple, however it is possible to create tuples "
"which contain mutable objects, such as lists."
msgstr ""
"输出时，元组都要由圆括号标注，这样才能正确地解释嵌套元组。输入时，圆括号可有可无，不过经常是必须的（如果元组是更大的表达式的一部分）。不允许为元组中的单个元素赋值，当然，可以创建含列表等可变对象的元组。"

#: ../../tutorial/datastructures.rst:408
msgid ""
"Though tuples may seem similar to lists, they are often used in different "
"situations and for different purposes. Tuples are :term:`immutable`, and "
"usually contain a heterogeneous sequence of elements that are accessed via "
"unpacking (see later in this section) or indexing (or even by attribute in "
"the case of :func:`namedtuples <collections.namedtuple>`). Lists are "
":term:`mutable`, and their elements are usually homogeneous and are accessed"
" by iterating over the list."
msgstr ""
"虽然，元组与列表很像，但使用场景不同，用途也不同。元组是 :term:`immutable` "
"（不可变的），一般可包含异质元素序列，通过解包（见本节下文）或索引访问（如果是 :func:`namedtuples "
"<collections.namedtuple>`，可以属性访问）。列表是 :term:`mutable` "
"（可变的），列表元素一般为同质类型，可迭代访问。"

#: ../../tutorial/datastructures.rst:416
msgid ""
"A special problem is the construction of tuples containing 0 or 1 items: the"
" syntax has some extra quirks to accommodate these.  Empty tuples are "
"constructed by an empty pair of parentheses; a tuple with one item is "
"constructed by following a value with a comma (it is not sufficient to "
"enclose a single value in parentheses). Ugly, but effective.  For example::"
msgstr ""
"构造 0 个或 1 "
"个元素的元组比较特殊：为了适应这种情况，对句法有一些额外的改变。用一对空圆括号就可以创建空元组；只有一个元素的元组可以通过在这个元素后添加逗号来构建（圆括号里只有一个值的话不够明确）。丑陋，但是有效。例如："

#: ../../tutorial/datastructures.rst:431
msgid ""
"The statement ``t = 12345, 54321, 'hello!'`` is an example of *tuple "
"packing*: the values ``12345``, ``54321`` and ``'hello!'`` are packed "
"together in a tuple. The reverse operation is also possible::"
msgstr ""
"语句 ``t = 12345, 54321, 'hello!'`` 是 *元组打包* 的例子：值 ``12345``, ``54321`` 和 "
"``'hello!'`` 一起被打包进元组。逆操作也可以："

#: ../../tutorial/datastructures.rst:437
msgid ""
"This is called, appropriately enough, *sequence unpacking* and works for any"
" sequence on the right-hand side.  Sequence unpacking requires that there "
"are as many variables on the left side of the equals sign as there are "
"elements in the sequence.  Note that multiple assignment is really just a "
"combination of tuple packing and sequence unpacking."
msgstr ""
"称之为 *序列解包*  "
"也是妥妥的，适用于右侧的任何序列。序列解包时，左侧变量与右侧序列元素的数量应相等。注意，多重赋值其实只是元组打包和序列解包的组合。"

#: ../../tutorial/datastructures.rst:447
msgid "Sets"
msgstr "集合"

#: ../../tutorial/datastructures.rst:449
msgid ""
"Python also includes a data type for *sets*.  A set is an unordered "
"collection with no duplicate elements.  Basic uses include membership "
"testing and eliminating duplicate entries.  Set objects also support "
"mathematical operations like union, intersection, difference, and symmetric "
"difference."
msgstr ""
"Python 还支持 *集合* "
"这种数据类型。集合是由不重复元素组成的无序容器。基本用法包括成员检测、消除重复元素。集合对象支持合集、交集、差集、对称差分等数学运算。"

#: ../../tutorial/datastructures.rst:454
msgid ""
"Curly braces or the :func:`set` function can be used to create sets.  Note: "
"to create an empty set you have to use ``set()``, not ``{}``; the latter "
"creates an empty dictionary, a data structure that we discuss in the next "
"section."
msgstr ""
"创建集合用花括号或 :func:`set` 函数。注意，创建空集合只能用 ``set()``，不能用 ``{}``，``{}`` "
"创建的是空字典，下一小节介绍数据结构：字典。"

#: ../../tutorial/datastructures.rst:458
msgid "Here is a brief demonstration::"
msgstr "以下是一些简单的示例 ::"

#: ../../tutorial/datastructures.rst:483
msgid ""
"Similarly to :ref:`list comprehensions <tut-listcomps>`, set comprehensions "
"are also supported::"
msgstr "与 :ref:`列表推导式 <tut-listcomps>` 类似，集合也支持推导式："

#: ../../tutorial/datastructures.rst:494
msgid "Dictionaries"
msgstr "字典"

#: ../../tutorial/datastructures.rst:496
msgid ""
"Another useful data type built into Python is the *dictionary* (see "
":ref:`typesmapping`). Dictionaries are sometimes found in other languages as"
" \"associative memories\" or \"associative arrays\".  Unlike sequences, "
"which are indexed by a range of numbers, dictionaries are indexed by *keys*,"
" which can be any immutable type; strings and numbers can always be keys.  "
"Tuples can be used as keys if they contain only strings, numbers, or tuples;"
" if a tuple contains any mutable object either directly or indirectly, it "
"cannot be used as a key. You can't use lists as keys, since lists can be "
"modified in place using index assignments, slice assignments, or methods "
"like :meth:`append` and :meth:`extend`."
msgstr ""
"*字典* （参见 :ref:`typesmapping`） 也是一种常用的 Python 內置数据类型。其他语言可能把字典称为 *联合内存* 或 "
"*联合数组*。与以连续整数为索引的序列不同，字典以 *关键字* "
"为索引，关键字通常是字符串或数字，也可以是其他任意不可变类型。只包含字符串、数字、元组的元组，也可以用作关键字。但如果元组直接或间接地包含了可变对象，就不能用作关键字。列表不能当关键字，因为列表可以用索引、切片、:meth:`append`"
" 、:meth:`extend` 等方法修改。"

#: ../../tutorial/datastructures.rst:507
msgid ""
"It is best to think of a dictionary as a set of *key: value* pairs, with the"
" requirement that the keys are unique (within one dictionary). A pair of "
"braces creates an empty dictionary: ``{}``. Placing a comma-separated list "
"of key:value pairs within the braces adds initial key:value pairs to the "
"dictionary; this is also the way dictionaries are written on output."
msgstr ""
"可以把字典理解为 *键值对* 的集合，但字典的键必须是唯一的。花括号 ``{}`` "
"用于创建空字典。另一种初始化字典的方式是，在花括号里输入逗号分隔的键值对，这也是字典的输出方式。"

#: ../../tutorial/datastructures.rst:513
msgid ""
"The main operations on a dictionary are storing a value with some key and "
"extracting the value given the key.  It is also possible to delete a "
"key:value pair with ``del``. If you store using a key that is already in "
"use, the old value associated with that key is forgotten.  It is an error to"
" extract a value using a non-existent key."
msgstr ""
"字典的主要用途是通过关键字存储、提取值。用 ``del`` "
"可以删除键值对。用已存在的关键字存储值，与该关键字关联的旧值会被取代。通过不存在的键提取值，则会报错。"

#: ../../tutorial/datastructures.rst:519
msgid ""
"Performing ``list(d)`` on a dictionary returns a list of all the keys used "
"in the dictionary, in insertion order (if you want it sorted, just use "
"``sorted(d)`` instead). To check whether a single key is in the dictionary, "
"use the :keyword:`in` keyword."
msgstr ""
"对字典执行 ``list(d)`` 操作，返回该字典中所有键的列表，按插入次序排列（如需排序，请使用 "
"``sorted(d)``）。检查字典里是否存在某个键，使用关键字 :keyword:`in`。"

#: ../../tutorial/datastructures.rst:524
msgid "Here is a small example using a dictionary::"
msgstr "以下是一些字典的简单示例："

#: ../../tutorial/datastructures.rst:545
msgid ""
"The :func:`dict` constructor builds dictionaries directly from sequences of "
"key-value pairs::"
msgstr ":func:`dict` 构造函数可以直接用键值对序列创建字典："

#: ../../tutorial/datastructures.rst:551
msgid ""
"In addition, dict comprehensions can be used to create dictionaries from "
"arbitrary key and value expressions::"
msgstr "字典推导式可以用任意键值表达式创建字典："

#: ../../tutorial/datastructures.rst:557
msgid ""
"When the keys are simple strings, it is sometimes easier to specify pairs "
"using keyword arguments::"
msgstr "关键字是比较简单的字符串时，直接用关键字参数指定键值对更便捷："

#: ../../tutorial/datastructures.rst:567
msgid "Looping Techniques"
msgstr "循环的技巧"

#: ../../tutorial/datastructures.rst:569
msgid ""
"When looping through dictionaries, the key and corresponding value can be "
"retrieved at the same time using the :meth:`items` method. ::"
msgstr "在字典中循环时，用 :meth:`items` 方法可同时取出键和对应的值："

#: ../../tutorial/datastructures.rst:579
msgid ""
"When looping through a sequence, the position index and corresponding value "
"can be retrieved at the same time using the :func:`enumerate` function. ::"
msgstr "在序列中循环时，用 :func:`enumerate` 函数可以同时取出位置索引和对应的值："

#: ../../tutorial/datastructures.rst:589
msgid ""
"To loop over two or more sequences at the same time, the entries can be "
"paired with the :func:`zip` function. ::"
msgstr "同时循环两个或多个序列时，用 :func:`zip` 函数可以将其内的元素一一匹配："

#: ../../tutorial/datastructures.rst:601
msgid ""
"To loop over a sequence in reverse, first specify the sequence in a forward "
"direction and then call the :func:`reversed` function. ::"
msgstr "为了逆向对序列进行循环，可以求出欲循环的正向序列，然后调用 :func:`reversed` 函数："

#: ../../tutorial/datastructures.rst:613
msgid ""
"To loop over a sequence in sorted order, use the :func:`sorted` function "
"which returns a new sorted list while leaving the source unaltered. ::"
msgstr "按指定顺序循环序列，可以用 :func:`sorted` 函数，在不改动原序列的基础上，返回一个重新的序列："

#: ../../tutorial/datastructures.rst:625
msgid ""
"It is sometimes tempting to change a list while you are looping over it; "
"however, it is often simpler and safer to create a new list instead. ::"
msgstr "一般来说，在循环中修改列表的内容时，创建新列表比较简单，且安全："

#: ../../tutorial/datastructures.rst:642
msgid "More on Conditions"
msgstr "深入条件控制"

#: ../../tutorial/datastructures.rst:644
msgid ""
"The conditions used in ``while`` and ``if`` statements can contain any "
"operators, not just comparisons."
msgstr "``while`` 和 ``if`` 条件句不只可以进行比较，还可以使用任意运算符。"

#: ../../tutorial/datastructures.rst:647
msgid ""
"The comparison operators ``in`` and ``not in`` check whether a value occurs "
"(does not occur) in a sequence.  The operators ``is`` and ``is not`` compare"
" whether two objects are really the same object; this only matters for "
"mutable objects like lists.  All comparison operators have the same "
"priority, which is lower than that of all numerical operators."
msgstr ""
"比较操作符 ``in`` 和 ``not in`` 校验一个值是否在（或不在）一个序列里。操作符 ``is`` 和 ``is not`` "
"比较两个对象是不是同一个对象，这只对像列表这样的可变对象比较重要。所有的比较操作符都有相同的优先级，且这个优先级比数值运算符低。"

#: ../../tutorial/datastructures.rst:653
msgid ""
"Comparisons can be chained.  For example, ``a < b == c`` tests whether ``a``"
" is less than ``b`` and moreover ``b`` equals ``c``."
msgstr "比较操作支持链式操作。例如，``a < b == c`` 校验 ``a`` 是否小于 ``b``，且 ``b`` 是否等于 ``c``。"

#: ../../tutorial/datastructures.rst:656
msgid ""
"Comparisons may be combined using the Boolean operators ``and`` and ``or``, "
"and the outcome of a comparison (or of any other Boolean expression) may be "
"negated with ``not``.  These have lower priorities than comparison "
"operators; between them, ``not`` has the highest priority and ``or`` the "
"lowest, so that ``A and not B or C`` is equivalent to ``(A and (not B)) or "
"C``. As always, parentheses can be used to express the desired composition."
msgstr ""
"比较操作可以用布尔运算符 ``and`` 和 ``or`` 组合，并且，比较操作（或其他布尔运算）的结果都可以用 ``not`` "
"取反。这些操作符的优先级低于比较操作符；``not`` 的优先级最高， ``or`` 的优先级最低，因此，``A and not B or C`` "
"等价于 ``(A and (not B)) or C``。与其他运算符操作一样，此处也可以用圆括号表示想要的组合。"

#: ../../tutorial/datastructures.rst:663
msgid ""
"The Boolean operators ``and`` and ``or`` are so-called *short-circuit* "
"operators: their arguments are evaluated from left to right, and evaluation "
"stops as soon as the outcome is determined.  For example, if ``A`` and ``C``"
" are true but ``B`` is false, ``A and B and C`` does not evaluate the "
"expression ``C``.  When used as a general value and not as a Boolean, the "
"return value of a short-circuit operator is the last evaluated argument."
msgstr ""
"布尔运算符 ``and`` 和 ``or`` 是所谓的 *短路* 运算符：其参数从左至右求值，一旦可以确定结果，求值就会停止。例如，如果 ``A`` 和"
" ``C`` 为真，``B`` 为假，那么 ``A and B and C`` 不会对 ``C`` "
"求值。用作普通值而不是布尔值时，短路运算符的返回值通常是最后一个求了值的参数。"

#: ../../tutorial/datastructures.rst:670
msgid ""
"It is possible to assign the result of a comparison or other Boolean "
"expression to a variable.  For example, ::"
msgstr "还可以把比较运算或其它布尔表达式的结果赋值给变量，例如："

#: ../../tutorial/datastructures.rst:678
msgid ""
"Note that in Python, unlike C, assignment inside expressions must be done "
"explicitly with the :ref:`walrus operator <why-can-t-i-use-an-assignment-in-"
"an-expression>` ``:=``. This avoids a common class of problems encountered "
"in C programs: typing ``=`` in an expression when ``==`` was intended."
msgstr ""
"注意，Python 与 C 不同，在表达式内部赋值必须显式使用 :ref:`海象运算符 <why-can-t-i-use-an-assignment-"
"in-an-expression>` ``:=``。 这避免了 C 程序中常见的问题：要在表达式中写 ``==`` 时，却写成了 ``=``。"

#: ../../tutorial/datastructures.rst:688
msgid "Comparing Sequences and Other Types"
msgstr "序列和其他类型的比较"

#: ../../tutorial/datastructures.rst:689
msgid ""
"Sequence objects typically may be compared to other objects with the same "
"sequence type. The comparison uses *lexicographical* ordering: first the "
"first two items are compared, and if they differ this determines the outcome"
" of the comparison; if they are equal, the next two items are compared, and "
"so on, until either sequence is exhausted. If two items to be compared are "
"themselves sequences of the same type, the lexicographical comparison is "
"carried out recursively.  If all items of two sequences compare equal, the "
"sequences are considered equal. If one sequence is an initial sub-sequence "
"of the other, the shorter sequence is the smaller (lesser) one.  "
"Lexicographical ordering for strings uses the Unicode code point number to "
"order individual characters. Some examples of comparisons between sequences "
"of the same type::"
msgstr ""
"序列对象可以与相同序列类型的其他对象比较。这种比较使用 *字典式* "
"顺序：首先，比较前两个对应元素，如果不相等，则可确定比较结果；如果相等，则比较之后的两个元素，以此类推，直到其中一个序列结束。如果要比较的两个元素本身是相同类型的序列，则递归地执行字典式顺序比较。如果两个序列中所有的对应元素都相等，则两个序列相等。如果一个序列是另一个的初始子序列，则较短的序列可被视为较小（较少）的序列。"
" 对于字符串来说，字典式顺序使用 Unicode 码位序号排序单个字符。下面列出了一些比较相同类型序列的例子："

#: ../../tutorial/datastructures.rst:709
msgid ""
"Note that comparing objects of different types with ``<`` or ``>`` is legal "
"provided that the objects have appropriate comparison methods.  For example,"
" mixed numeric types are compared according to their numeric value, so 0 "
"equals 0.0, etc.  Otherwise, rather than providing an arbitrary ordering, "
"the interpreter will raise a :exc:`TypeError` exception."
msgstr ""
"注意，当比较不同类型的对象时，只要待比较的对象提供了合适的比较方法，就可以使用 ``<`` 和 ``>`` "
"进行比较。例如，混合的数字类型通过数字值进行比较，所以，0 等于 0.0，等等。如果没有提供合适的比较方法，解释器不会随便给出一个比较结果，而是引发 "
":exc:`TypeError` 异常。"

#: ../../tutorial/datastructures.rst:717
msgid "Footnotes"
msgstr "备注"

#: ../../tutorial/datastructures.rst:718
msgid ""
"Other languages may return the mutated object, which allows method chaining,"
" such as ``d->insert(\"a\")->remove(\"b\")->sort();``."
msgstr "别的语言可能会将可变对象返回，允许方法连续执行，例如 ``d->insert(\"a\")->remove(\"b\")->sort();``。"