datastructures.po

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msgstr ""
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#:../../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. Similar to ``a[len(a):] = [x]``."
msgstr"在列表末尾添加一项。 类似于 ``a[len(a):] = [x]``。"

#:../../tutorial/datastructures.rst:28
msgid""
"Extend the list by appending all the items from the iterable. Similar to "
"``a[len(a):] = iterable``."
msgstr"通过添加来自 iterable 的所有项来扩展列表。 类似于 ``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. It raises an :exc:`IndexError` if the list is empty or the index is "
"outside the list range."
msgstr""
"移除列表中给定位置上的条目，并返回该条目。 如果未指定索引号，则 ``a.pop()`` 将移除并返回列表中的最后一个条目。 "
"如果列表为空或索引号在列表索引范围之外则会引发 :exc:`IndexError`。"

#:../../tutorial/datastructures.rst:59
msgid"Remove all items from the list. Similar to ``del a[:]``."
msgstr"移除列表中的所有项。 类似于 ``del a[:]``。"

#:../../tutorial/datastructures.rst:65
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:68
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:77
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:83
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:90
msgid"Reverse the elements of the list in place."
msgstr"翻转列表中的元素。"

#:../../tutorial/datastructures.rst:96
msgid"Return a shallow copy of the list. Similar to ``a[:]``."
msgstr"返回列表的浅拷贝。 类似于 ``a[:]``。"

#:../../tutorial/datastructures.rst:99
msgid"An example that uses most of the list methods::"
msgstr"多数列表方法示例："

#:../../tutorial/datastructures.rst:101
msgid""
">>> fruits = ['orange', 'apple', 'pear', 'banana', 'kiwi', 'apple', 'banana']\n"
">>> fruits.count('apple')\n"
"2\n"
">>> fruits.count('tangerine')\n"
"0\n"
">>> fruits.index('banana')\n"
"3\n"
">>> fruits.index('banana', 4) # Find next banana starting at position 4\n"
"6\n"
">>> fruits.reverse()\n"
">>> fruits\n"
"['banana', 'apple', 'kiwi', 'banana', 'pear', 'apple', 'orange']\n"
">>> fruits.append('grape')\n"
">>> fruits\n"
"['banana', 'apple', 'kiwi', 'banana', 'pear', 'apple', 'orange', 'grape']\n"
">>> fruits.sort()\n"
">>> fruits\n"
"['apple', 'apple', 'banana', 'banana', 'grape', 'kiwi', 'orange', 'pear']\n"
">>> fruits.pop()\n"
"'pear'"
msgstr""
">>> fruits = ['orange', 'apple', 'pear', 'banana', 'kiwi', 'apple', 'banana']\n"
">>> fruits.count('apple')\n"
"2\n"
">>> fruits.count('tangerine')\n"
"0\n"
">>> fruits.index('banana')\n"
"3\n"
">>> fruits.index('banana', 4) # 从 4 号位开始查找下一个 banana\n"
"6\n"
">>> fruits.reverse()\n"
">>> fruits\n"
"['banana', 'apple', 'kiwi', 'banana', 'pear', 'apple', 'orange']\n"
">>> fruits.append('grape')\n"
">>> fruits\n"
"['banana', 'apple', 'kiwi', 'banana', 'pear', 'apple', 'orange', 'grape']\n"
">>> fruits.sort()\n"
">>> fruits\n"
"['apple', 'apple', 'banana', 'banana', 'grape', 'kiwi', 'orange', 'pear']\n"
">>> fruits.pop()\n"
"'pear'"

#:../../tutorial/datastructures.rst:122
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``. [#]_ This is a design principle for all mutable data "
"structures in Python."
msgstr""
"你可能已经注意到 ``insert``, ``remove`` 或 ``sort`` 等仅修改列表的方法都不会打印返回值 -- 它们返回默认值 "
"``None``。 [#]_ 这是适用于 Python 中所有可变数据结构的设计原则。"

#:../../tutorial/datastructures.rst:127
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""
"你可能会注意到的另一件事是并非所有数据都可以排序或比较。 举例来说，``[None, 'hello', 10]`` 就不可排序因为整数不能与字符串比较而"
" ``None`` 不能与其他类型比较。 此外，还存在一些没有定义顺序关系的类型。 例如，``3+4j < 5+7j`` 就不是一个合法的比较。"

#:../../tutorial/datastructures.rst:138
msgid"Using Lists as Stacks"
msgstr"用列表实现堆栈"

#:../../tutorial/datastructures.rst:143
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""
"列表方法使得将列表用作栈非常容易，最后添加的元素会最先被取出（“后进先出”）。 要将一个条目添加到栈顶，可使用 :meth:`!append`。 "
"要从栈顶取出一个条目，则使用 :meth:`!pop` 且不必显式指定索引。 例如::"

#:../../tutorial/datastructures.rst:148
msgid""
">>> stack = [3, 4, 5]\n"
">>> stack.append(6)\n"
">>> stack.append(7)\n"
">>> stack\n"
"[3, 4, 5, 6, 7]\n"
">>> stack.pop()\n"
"7\n"
">>> stack\n"
"[3, 4, 5, 6]\n"
">>> stack.pop()\n"
"6\n"
">>> stack.pop()\n"
"5\n"
">>> stack\n"
"[3, 4]"
msgstr""
">>> stack = [3, 4, 5]\n"
">>> stack.append(6)\n"
">>> stack.append(7)\n"
">>> stack\n"
"[3, 4, 5, 6, 7]\n"
">>> stack.pop()\n"
"7\n"
">>> stack\n"
"[3, 4, 5, 6]\n"
">>> stack.pop()\n"
"6\n"
">>> stack.pop()\n"
"5\n"
">>> stack\n"
"[3, 4]"

#:../../tutorial/datastructures.rst:168
msgid"Using Lists as Queues"
msgstr"用列表实现队列"

#:../../tutorial/datastructures.rst:172
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:178
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:181
msgid""
">>> from collections import deque\n"
">>> queue = deque([\"Eric\", \"John\", \"Michael\"])\n"
">>> queue.append(\"Terry\") # Terry arrives\n"
">>> queue.append(\"Graham\") # Graham arrives\n"
">>> queue.popleft() # The first to arrive now leaves\n"
"'Eric'\n"
">>> queue.popleft() # The second to arrive now leaves\n"
"'John'\n"
">>> queue # Remaining queue in order of arrival\n"
"deque(['Michael', 'Terry', 'Graham'])"
msgstr""
">>> from collections import deque\n"
">>> queue = deque([\"Eric\", \"John\", \"Michael\"])\n"
">>> queue.append(\"Terry\") # Terry 到了\n"
">>> queue.append(\"Graham\") # Graham 到了\n"
">>> queue.popleft() # 第一个到的现在走了\n"
"'Eric'\n"
">>> queue.popleft() # 第二个到的现在走了\n"
"'John'\n"
">>> queue # 按到达顺序排列的剩余队列\n"
"deque(['Michael', 'Terry', 'Graham'])"

#:../../tutorial/datastructures.rst:196
msgid"List Comprehensions"
msgstr"列表推导式"

#:../../tutorial/datastructures.rst:198
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:203
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:205
msgid""
">>> squares = []\n"
">>> for x in range(10):\n"
"... squares.append(x**2)\n"
"...\n"
">>> squares\n"
"[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]"
msgstr""
">>> squares = []\n"
">>> for x in range(10):\n"
"... squares.append(x**2)\n"
"...\n"
">>> squares\n"
"[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]"

#:../../tutorial/datastructures.rst:212
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:216
msgid"squares = list(map(lambda x: x**2, range(10)))"
msgstr"squares = list(map(lambda x: x**2, range(10)))"

#:../../tutorial/datastructures.rst:218
msgid"or, equivalently::"
msgstr"或等价于："

#:../../tutorial/datastructures.rst:220
msgid"squares = [x**2 for x in range(10)]"
msgstr"squares = [x**2 for x in range(10)]"

#:../../tutorial/datastructures.rst:222
msgid"which is more concise and readable."
msgstr"上面这种写法更简洁、易读。"

#:../../tutorial/datastructures.rst:224
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:231
msgid""
">>> [(x, y) for x in [1,2,3] for y in [3,1,4] if x != y]\n"
"[(1, 3), (1, 4), (2, 3), (2, 1), (2, 4), (3, 1), (3, 4)]"
msgstr""
">>> [(x, y) for x in [1,2,3] for y in [3,1,4] if x != y]\n"
"[(1, 3), (1, 4), (2, 3), (2, 1), (2, 4), (3, 1), (3, 4)]"

#:../../tutorial/datastructures.rst:234
msgid"and it's equivalent to::"
msgstr"等价于："

#:../../tutorial/datastructures.rst:236
msgid""
">>> combs = []\n"
">>> for x in [1,2,3]:\n"
"... for y in [3,1,4]:\n"
"... if x != y:\n"
"... combs.append((x, y))\n"
"...\n"
">>> combs\n"
"[(1, 3), (1, 4), (2, 3), (2, 1), (2, 4), (3, 1), (3, 4)]"
msgstr""
">>> combs = []\n"
">>> for x in [1,2,3]:\n"
"... for y in [3,1,4]:\n"
"... if x != y:\n"
"... combs.append((x, y))\n"
"...\n"
">>> combs\n"
"[(1, 3), (1, 4), (2, 3), (2, 1), (2, 4), (3, 1), (3, 4)]"

#:../../tutorial/datastructures.rst:245
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:248
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:251
msgid""
">>> vec = [-4, -2, 0, 2, 4]\n"
">>> # create a new list with the values doubled\n"
">>> [x*2 for x in vec]\n"
"[-8, -4, 0, 4, 8]\n"
">>> # filter the list to exclude negative numbers\n"
">>> [x for x in vec if x >= 0]\n"
"[0, 2, 4]\n"
">>> # apply a function to all the elements\n"
">>> [abs(x) for x in vec]\n"
"[4, 2, 0, 2, 4]\n"
">>> # call a method on each element\n"
">>> freshfruit = [' banana', ' loganberry ', 'passion fruit ']\n"
">>> [weapon.strip() for weapon in freshfruit]\n"
"['banana', 'loganberry', 'passion fruit']\n"
">>> # create a list of 2-tuples like (number, square)\n"
">>> [(x, x**2) for x in range(6)]\n"
"[(0, 0), (1, 1), (2, 4), (3, 9), (4, 16), (5, 25)]\n"
">>> # the tuple must be parenthesized, otherwise an error is raised\n"
">>> [x, x**2 for x in range(6)]\n"
" File \"<stdin>\", line 1\n"
" [x, x**2 for x in range(6)]\n"
" ^^^^^^^\n"
"SyntaxError: did you forget parentheses around the comprehension target?\n"
">>> # flatten a list using a listcomp with two 'for'\n"
">>> vec = [[1,2,3], [4,5,6], [7,8,9]]\n"
">>> [num for elem in vec for num in elem]\n"
"[1, 2, 3, 4, 5, 6, 7, 8, 9]"
msgstr""
">>> vec = [-4, -2, 0, 2, 4]\n"
">>> # 新建一个将值翻倍的列表\n"
">>> [x*2 for x in vec]\n"
"[-8, -4, 0, 4, 8]\n"
">>> # 过滤列表以排除负数\n"
">>> [x for x in vec if x >= 0]\n"
"[0, 2, 4]\n"
">>> # 对所有元素应用一个函数\n"
">>> [abs(x) for x in vec]\n"
"[4, 2, 0, 2, 4]\n"
">>> # 在每个元素上调用一个方法\n"
">>> freshfruit = [' banana', ' loganberry ', 'passion fruit ']\n"
">>> [weapon.strip() for weapon in freshfruit]\n"
"['banana', 'loganberry', 'passion fruit']\n"
">>> # 创建一个包含 (数字, 平方) 2 元组的列表\n"
">>> [(x, x**2) for x in range(6)]\n"
"[(0, 0), (1, 1), (2, 4), (3, 9), (4, 16), (5, 25)]\n"
">>> # 元组必须加圆括号，否则会引发错误\n"
">>> [x, x**2 for x in range(6)]\n"
" File \"<stdin>\", line 1\n"
" [x, x**2 for x in range(6)]\n"
" ^^^^^^^\n"
"SyntaxError: did you forget parentheses around the comprehension target?\n"
">>> # 使用两个 'for' 来展平嵌套的列表\n"
">>> vec = [[1,2,3], [4,5,6], [7,8,9]]\n"
">>> [num for elem in vec for num in elem]\n"
"[1, 2, 3, 4, 5, 6, 7, 8, 9]"

#:../../tutorial/datastructures.rst:279
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:281
msgid""
">>> from math import pi\n"
">>> [str(round(pi, i)) for i in range(1, 6)]\n"
"['3.1', '3.14', '3.142', '3.1416', '3.14159']"
msgstr""
">>> from math import pi\n"
">>> [str(round(pi, i)) for i in range(1, 6)]\n"
"['3.1', '3.14', '3.142', '3.1416', '3.14159']"

#:../../tutorial/datastructures.rst:286
msgid"Nested List Comprehensions"
msgstr"嵌套的列表推导式"

#:../../tutorial/datastructures.rst:288
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:291
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:294
msgid""
">>> matrix = [\n"
"... [1, 2, 3, 4],\n"
"... [5, 6, 7, 8],\n"
"... [9, 10, 11, 12],\n"
"... ]"
msgstr""
">>> matrix = [\n"
"... [1, 2, 3, 4],\n"
"... [5, 6, 7, 8],\n"
"... [9, 10, 11, 12],\n"
"... ]"

#:../../tutorial/datastructures.rst:300
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:302
msgid""
">>> [[row[i] for row in matrix] for i in range(4)]\n"
"[[1, 5, 9], [2, 6, 10], [3, 7, 11], [4, 8, 12]]"
msgstr""
">>> [[row[i] for row in matrix] for i in range(4)]\n"
"[[1, 5, 9], [2, 6, 10], [3, 7, 11], [4, 8, 12]]"

#:../../tutorial/datastructures.rst:305
msgid""
"As we saw in the previous section, the inner list comprehension is evaluated"
" in the context of the :keyword:`for` that follows it, so this example is "
"equivalent to::"
msgstr"如我们在之前小节中看到的，内部的列表推导式是在它之后的 :keyword:`for` 的上下文中被求值的，所以这个例子等价于::"

#:../../tutorial/datastructures.rst:309
msgid""
">>> transposed = []\n"
">>> for i in range(4):\n"
"... transposed.append([row[i] for row in matrix])\n"
"...\n"
">>> transposed\n"
"[[1, 5, 9], [2, 6, 10], [3, 7, 11], [4, 8, 12]]"
msgstr""
">>> transposed = []\n"
">>> for i in range(4):\n"
"... transposed.append([row[i] for row in matrix])\n"
"...\n"
">>> transposed\n"
"[[1, 5, 9], [2, 6, 10], [3, 7, 11], [4, 8, 12]]"

#:../../tutorial/datastructures.rst:316
msgid"which, in turn, is the same as::"
msgstr"反过来说，也等价于："

#:../../tutorial/datastructures.rst:318
msgid""
">>> transposed = []\n"
">>> for i in range(4):\n"
"... # the following 3 lines implement the nested listcomp\n"
"... transposed_row = []\n"
"... for row in matrix:\n"
"... transposed_row.append(row[i])\n"
"... transposed.append(transposed_row)\n"
"...\n"
">>> transposed\n"
"[[1, 5, 9], [2, 6, 10], [3, 7, 11], [4, 8, 12]]"
msgstr""
">>> transposed = []\n"
">>> for i in range(4):\n"
"... # 以下 3 行实现了嵌套的列表组\n"
"... transposed_row = []\n"
"... for row in matrix:\n"
"... transposed_row.append(row[i])\n"
"... transposed.append(transposed_row)\n"
"...\n"
">>> transposed\n"
"[[1, 5, 9], [2, 6, 10], [3, 7, 11], [4, 8, 12]]"

#:../../tutorial/datastructures.rst:329
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:332
msgid""
">>> list(zip(*matrix))\n"
"[(1, 5, 9), (2, 6, 10), (3, 7, 11), (4, 8, 12)]"
msgstr""
">>> list(zip(*matrix))\n"
"[(1, 5, 9), (2, 6, 10), (3, 7, 11), (4, 8, 12)]"

#:../../tutorial/datastructures.rst:335
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:340
msgid"The :keyword:`!del` statement"
msgstr":keyword:`!del` 语句"

#:../../tutorial/datastructures.rst:342
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""
"可以按索引而不是按值从一个列表移除条目：即使用 :keyword:`del` 语句。 这不同于返回一个值的 :meth:`!pop` 方法。 "
":keyword:`!del` 语句还可被用来从列表移除切片或清空整个列表（之前我们通过将一个空列表赋值给切片实现此功能）。 例如::"

#:../../tutorial/datastructures.rst:348
msgid""
">>> a = [-1, 1, 66.25, 333, 333, 1234.5]\n"
">>> del a[0]\n"
">>> a\n"
"[1, 66.25, 333, 333, 1234.5]\n"
">>> del a[2:4]\n"
">>> a\n"
"[1, 66.25, 1234.5]\n"
">>> del a[:]\n"
">>> a\n"
"[]"
msgstr""
">>> a = [-1, 1, 66.25, 333, 333, 1234.5]\n"
">>> del a[0]\n"
">>> a\n"
"[1, 66.25, 333, 333, 1234.5]\n"
">>> del a[2:4]\n"
">>> a\n"
"[1, 66.25, 1234.5]\n"
">>> del a[:]\n"
">>> a\n"
"[]"

#:../../tutorial/datastructures.rst:359
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:361
msgid">>> del a"
msgstr">>> del a"

#:../../tutorial/datastructures.rst:363
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:370
msgid"Tuples and Sequences"
msgstr"元组和序列"

#:../../tutorial/datastructures.rst:372
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:378
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:380
msgid""
">>> t = 12345, 54321, 'hello!'\n"
">>> t[0]\n"
"12345\n"
">>> t\n"
"(12345, 54321, 'hello!')\n"
">>> # Tuples may be nested:\n"
">>> u = t, (1, 2, 3, 4, 5)\n"
">>> u\n"
"((12345, 54321, 'hello!'), (1, 2, 3, 4, 5))\n"
">>> # Tuples are immutable:\n"
">>> t[0] = 88888\n"
"Traceback (most recent call last):\n"
" File \"<stdin>\", line 1, in <module>\n"
"TypeError: 'tuple' object does not support item assignment\n"
">>> # but they can contain mutable objects:\n"
">>> v = ([1, 2, 3], [3, 2, 1])\n"
">>> v\n"
"([1, 2, 3], [3, 2, 1])"
msgstr""
">>> t = 12345, 54321, 'hello!'\n"
">>> t[0]\n"
"12345\n"
">>> t\n"
"(12345, 54321, 'hello!')\n"
">>> # 元组可以嵌套：\n"
">>> u = t, (1, 2, 3, 4, 5)\n"
">>> u\n"
"((12345, 54321, 'hello!'), (1, 2, 3, 4, 5))\n"
">>> # 元组是不可变对象：\n"
">>> t[0] = 88888\n"
"Traceback (most recent call last):\n"
" File \"<stdin>\", line 1, in <module>\n"
"TypeError: 'tuple' object does not support item assignment\n"
">>> # 但它们可以包含可变对象：\n"
">>> v = ([1, 2, 3], [3, 2, 1])\n"
">>> v\n"
"([1, 2, 3], [3, 2, 1])"

#:../../tutorial/datastructures.rst:400
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:407
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:415
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:421
msgid""
">>> empty = ()\n"
">>> singleton = 'hello', # <-- note trailing comma\n"
">>> len(empty)\n"
"0\n"
">>> len(singleton)\n"
"1\n"
">>> singleton\n"
"('hello',)"
msgstr""
">>> empty = ()\n"
">>> singleton = 'hello', # <-- 注意末尾的逗号\n"
">>> len(empty)\n"
"0\n"
">>> len(singleton)\n"
"1\n"
">>> singleton\n"
"('hello',)"

#:../../tutorial/datastructures.rst:430
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:434
msgid">>> x, y, z = t"
msgstr">>> x, y, z = t"

#:../../tutorial/datastructures.rst:436
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:446
msgid"Sets"
msgstr"集合"

#:../../tutorial/datastructures.rst:448
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:453
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:457
msgid"Here is a brief demonstration::"
msgstr"以下是一些简单的示例 ::"

#:../../tutorial/datastructures.rst:459
msgid""
">>> basket = {'apple', 'orange', 'apple', 'pear', 'orange', 'banana'}\n"
">>> print(basket) # show that duplicates have been removed\n"
"{'orange', 'banana', 'pear', 'apple'}\n"
">>> 'orange' in basket # fast membership testing\n"
"True\n"
">>> 'crabgrass' in basket\n"
"False\n"
"\n"
">>> # Demonstrate set operations on unique letters from two words\n"
">>>\n"
">>> a = set('abracadabra')\n"
">>> b = set('alacazam')\n"
">>> a # unique letters in a\n"
"{'a', 'r', 'b', 'c', 'd'}\n"
">>> a - b # letters in a but not in b\n"
"{'r', 'd', 'b'}\n"
">>> a | b # letters in a or b or both\n"
"{'a', 'c', 'r', 'd', 'b', 'm', 'z', 'l'}\n"
">>> a & b # letters in both a and b\n"
"{'a', 'c'}\n"
">>> a ^ b # letters in a or b but not both\n"
"{'r', 'd', 'b', 'm', 'z', 'l'}"
msgstr""
">>> basket = {'apple', 'orange', 'apple', 'pear', 'orange', 'banana'}\n"
">>> print(basket) # 显示重复项已被移除\n"
"{'orange', 'banana', 'pear', 'apple'}\n"
">>> 'orange' in basket # 快速成员检测\n"
"True\n"
">>> 'crabgrass' in basket\n"
"False\n"
"\n"
">>> # 演示针对两个单词中独有的字母进行集合运算\n"
">>>\n"
">>> a = set('abracadabra')\n"
">>> b = set('alacazam')\n"
">>> a # a 中独有的字母\n"
"{'a', 'r', 'b', 'c', 'd'}\n"
">>> a - b # 存在于 a 中但不存在于 b 中的字母\n"
"{'r', 'd', 'b'}\n"
">>> a | b # 存在于 a 或 b 中或两者中皆有的字母\n"
"{'a', 'c', 'r', 'd', 'b', 'm', 'z', 'l'}\n"
">>> a & b # 同时存在于 a 和 b 中的字母\n"
"{'a', 'c'}\n"
">>> a ^ b # 存在于 a 或 b 中但非两者中皆有的字母\n"
"{'r', 'd', 'b', 'm', 'z', 'l'}"

#:../../tutorial/datastructures.rst:482
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:485
msgid""
">>> a = {x for x in 'abracadabra' if x not in 'abc'}\n"
">>> a\n"
"{'r', 'd'}"
msgstr""
">>> a = {x for x in 'abracadabra' if x not in 'abc'}\n"
">>> a\n"
"{'r', 'd'}"

#:../../tutorial/datastructures.rst:493
msgid"Dictionaries"
msgstr"字典"

#:../../tutorial/datastructures.rst:495
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""
"另一个常用的 Python 内置数据类型是 *字典* (参见 :ref:`typesmapping`)。 "
"字典在其他编程语言中可能称为“联合内存”或“联合数组”。 与以连续整数为索引的序列不同，字典是以 *键* "
"来索引的，键可以是任何不可变类型；字符串和数字总是可以作为键。 "
"元组在其仅包含字符串、数字或元组时也可以作为键；如果一个元组直接或间接地包含了任何可变对象，则不可以用作键。 "
"你不能使用列表作为键，因为列表可使用索引赋值、切片赋值或 :meth:`!append` 和 :meth:`!extend` 等方法进行原地修改。"

#:../../tutorial/datastructures.rst:506
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:512
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:518
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:523
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:525
msgid""
">>> tel = {'jack': 4098, 'sape': 4139}\n"
">>> tel['guido'] = 4127\n"
">>> tel\n"
"{'jack': 4098, 'sape': 4139, 'guido': 4127}\n"
">>> tel['jack']\n"
"4098\n"
">>> del tel['sape']\n"
">>> tel['irv'] = 4127\n"
">>> tel\n"
"{'jack': 4098, 'guido': 4127, 'irv': 4127}\n"
">>> list(tel)\n"
"['jack', 'guido', 'irv']\n"
">>> sorted(tel)\n"
"['guido', 'irv', 'jack']\n"
">>> 'guido' in tel\n"
"True\n"
">>> 'jack' not in tel\n"
"False"
msgstr""
">>> tel = {'jack': 4098, 'sape': 4139}\n"
">>> tel['guido'] = 4127\n"
">>> tel\n"
"{'jack': 4098, 'sape': 4139, 'guido': 4127}\n"
">>> tel['jack']\n"
"4098\n"
">>> del tel['sape']\n"
">>> tel['irv'] = 4127\n"
">>> tel\n"
"{'jack': 4098, 'guido': 4127, 'irv': 4127}\n"
">>> list(tel)\n"
"['jack', 'guido', 'irv']\n"
">>> sorted(tel)\n"
"['guido', 'irv', 'jack']\n"
">>> 'guido' in tel\n"
"True\n"
">>> 'jack' not in tel\n"
"False"

#:../../tutorial/datastructures.rst:544
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:547
msgid""
">>> dict([('sape', 4139), ('guido', 4127), ('jack', 4098)])\n"
"{'sape': 4139, 'guido': 4127, 'jack': 4098}"
msgstr""
">>> dict([('sape', 4139), ('guido', 4127), ('jack', 4098)])\n"
"{'sape': 4139, 'guido': 4127, 'jack': 4098}"

#:../../tutorial/datastructures.rst:550
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:553
msgid""
">>> {x: x**2 for x in (2, 4, 6)}\n"
"{2: 4, 4: 16, 6: 36}"
msgstr""
">>> {x: x**2 for x in (2, 4, 6)}\n"
"{2: 4, 4: 16, 6: 36}"

#:../../tutorial/datastructures.rst:556
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:559
msgid""
">>> dict(sape=4139, guido=4127, jack=4098)\n"