云南大学数学与统计学院数学系信息与计算科学专业
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1.2.3 Python’s Built-In Classes
＊Python 的内建类
Table 1.2 provides a summary of commonly used, built-in
classes in Python; we take particular note of which classes are
mutable and which are immutable. A class is immutable if
each object of that class has a fixed value upon instantiation
that cannot subsequently be changed. For example, the float
class is immutable. Once an instance has been created, its value
cannot be changed (although an identifier referencing that
object can be reassigned to a different value).
＊表 1.2 提供了有关 Python 中常用的内置类的总结；我们
要特别注意哪些类是可变的，哪些是不可变的。如果该
类的每个对象在实例化后都具有固定值，而且不能随后
更改，那么这个类是不可变的。例如，float 类是不可变
的。实例一经创建，其值不能被更改（尽管可以将指向
该对象的标识符重新分配给不同的值）。
In this section, we provide an introduction to these classes,
discussing their purpose and presenting several means for
creating instances of the classes. Literal forms (such as 98.6)
exist for most of the built-in classes, and all of the classes
support a traditional constructor form that creates instances
that are based upon one or more existing values. Operators
supported by these classes are described in Section 1.3. More
detailed information about these classes can be found in later
chapters as follows: lists and tuples (Chapter 5); strings
(Chapters 5 and 13, and Appendix A); sets and dictionaries
(Chapter 10).
＊在本节中，我们将介绍这些类，讨论它们的存在意义
以及介绍几种创建类实例的方法。大多数内置类都有字
面形式（如 98.6），同时所有类都支持像构建函数那样
的构建形式，来创建基于一个或多个现有值的实例。这
些类支持的运算符在第 1.3 节中有描述。有关这些类的更
多详细信息，请参见以下章节：列表和元组（第 5 章）；
字符串（第 5 章和第 13 章以及附录 A）；集合和字典
（第 10 章）。
The bool Class
＊布尔类
The bool class is used to manipulate logical (Boolean) values,
and the only two instances of that class are expressed as the
literals True and False. The default constructor, bool(), returns
False, but there is no reason to use that syntax rather than the
more direct literal form. Python allows the creation of a
Boolean value from a nonboolean type using the syntax
bool(foo) for value foo. The interpretation depends upon the
type of the parameter. Numbers evaluate to False if zero, and
True if nonzero. Sequences and other container types, such as
strings and lists, evaluate to False if empty and True if nonempty.
An important application of this interpretation is the use of a
nonboolean value as a condition in a control structure.
＊bool 类用于操纵逻辑（布尔）值，该类的唯一两个实
例表示为 True 和 False。构造函数 bool()默认返回 False，
一般直接使用文字形式，而不是调用 bool()函数。Python
允许使用 bool(foo)语句，将非布尔类的值，转化为一个
布尔值。函数返回值取决于参数的类型：如果零，则评
估为 False，如果非零，则返回 True。序列以及其他的容
器类型，如字符串和列表，如果为空，则评估为 False，
如果非空，则评估为 True。这种解释，使得非布尔值也
可以作为控制结构中的判断条件。
The int Class
＊整数类
The int and float classes are the primary numeric types in
Python. The int class is designed to represent integer values
with arbitrary magnitude. Unlike Java and C++, which support
different integral types with different precisions (e.g., int,
short, long), Python automatically chooses the internal
representation for an integer based upon the magnitude of its
value. Typical literals for integers include 0,137, and -23. In
some contexts, it is convenient to express an integral value
using binary, octal, or hexadecimal. That can be done by using
a prefix of the number 0 and then a character to describe the
base. Example of such literals are respectively 0b1011, 0o52,
and 0x7f.
＊int 和 float 类是 Python 中的基本数字类型。int 类被设计
为表示任意大小的整数值。不像 Java 和 C++那样支持不
同精度（例如，int，short，long）的整数类型，Python 会
根据其值的大小自动选择整数的占用空间。整数的典型
样式包括 0,137 和-23。在某些情况下，使用二进制，八进
制或十六进制表达整数值会更加方便。这种非十进制的
表示方法可以这样写，用 0 作为前缀，其后跟着表示进位
制的英文首字母小写，之后跟着数字。例子中的表达式
分别为 0b1011，0o52 以及 0x7f。
The integer constructor, int(), returns value 0 by default. But
this constructor can be used to construct an integer value based
upon an existing value of another type. For example, if f
represents a floating-point value, the syntax int(f) produces the
truncated value of f. For example, both int(3.14) and int(3.99)
produce the value 3, while int(-3.9) produces the value -3. The
constructor can also be used to parse a string that is presumed
to represent an integral value (such as one entered by a user).
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