python内置模块--builtins

Python内置模块 builtins 概览，包括常见 FUNCTIONS 和基础 CLASSES。

打印 sys.builtin_module_names 可查看 python 解释器自带的基础模块：

>>> import sys
>>> sys.builtin_module_names
('_ast', '_codecs', '_collections', '_functools', '_imp', '_io', '_locale', '_operator', '_signal', '_sre', '_stat', '_string', '_symtable', '_thread', '_tracemalloc', '_warnings', '_weakref', 'atexit', 'builtins', 'errno', 'faulthandler', 'gc', 'itertools', 'marshal', 'posix', 'pwd', 'sys', 'time', 'xxsubtype', 'zipimport')

A tuple of strings giving the names of all modules that are compiled into this Python interpreter.

builtins

在 python help utility 交互控制台中，直接输入 builtins 可查看模块帮助。
在 python 交互控制台中，则先执行 import builtins 导入 builtins 模块，再调用 help(builtins) 查看模块帮助。

>>> import builtins
>>> help(builtins)

Help on built-in module builtins:

NAME
    builtins - Built-in functions, exceptions, and other objects.

DESCRIPTION
    Noteworthy: None is the `nil' object; Ellipsis represents `...' in slices.

• 执行 print(builtins.__doc__) 查看模块概要：

>>> import builtins
>>> print(builtins.__doc__)
Built-in functions, exceptions, and other objects.

Noteworthy: None is the `nil' object; Ellipsis represents `...' in slices.

• 执行 dir(builtins) 查看模块：

>>> import builtins
>>> dir(builtins)

> 也可执行 `print(builtins.__dict__)` 打印 builtins 模块的符号表。

Understanding Data Types in Python

以下先过滤内置模块中的公开符号，然后再进一步过滤出以“is”开头的判断接口：

>>> [n for n in dir(builtins) if not n.startswith('_') and n.startswith('is')]
['isinstance', 'issubclass']

FUNCTIONS

builtins 模块提供了一些常用的内置函数（FUNCTIONS），大概分为 vars、math、utility 三类：

vars

    globals()
        Return the dictionary containing the current scope's global variables.

    locals()
        Return a dictionary containing the current scope's local variables.

    vars(...)
        vars([object]) -> dictionary

        Without arguments, equivalent to locals().
        With an argument, equivalent to object.__dict__.

math

    abs(x, /)
        Return the absolute value of the argument.

    divmod(x, y, /)
        Return the tuple (x//y, x%y).  Invariant: div*y + mod == x.

    max(...)

    min(...)

    pow(x, y, z=None, /)
        Equivalent to x**y (with two arguments) or x**y % z (with three arguments)

    round(...)
        round(number[, ndigits]) -> number

    sorted(iterable, /, *, key=None, reverse=False)
        Return a new list containing all items from the iterable in ascending order.

    sum(iterable, start=0, /)
        Return the sum of a 'start' value (default: 0) plus an iterable of numbers

更多可参考 math、cmath 等 C 标准的数学库模块，或安装更专业的第三方科学计算库 SciPy 组织提供的 SciPy 和 NumPy。

inspect.isbuiltin

由于 python3 控制台 REPL 默认导入了 builtins 模块，因此可以直接输入函数符号名，如下显示则为内置函数：

>>> len
<built-in function len>
>>> open
<built-in function open>
>>> print
<built-in function print>

另外，也可通过 inspect.isbuiltin(object) 判断 object 是否为内置函数：

inspect.isbuiltin(object)
Return true if the object is a built-in function or a bound built-in method.

示例如下：

>>> inspect.isbuiltin(print)
True
>>> inspect.isbuiltin(len)
True
>>> inspect.isbuiltin(hex)
True
>>> inspect.isbuiltin(str)
False
>>> inspect.isbuiltin(string)
False

inspect in builtins

由于 python3 控制台 REPL 默认导入了 builtins 模块，因此可以直接输入类名，根据输出的提示信息判断是否为内建模块：

str 为内建类型（在 builtins 模块中），string 不是内建类型（但是标准库）：

>>> str
<class 'str'>

>>> string
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'string' is not defined

enumerate 为内建类型，enum 不是内建类型：

>>> enum
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'enum' is not defined

>>> enumerate
<class 'enumerate'>

date 和 datetime 非内建类型：

>>> date
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'date' is not defined

>>> datetime
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'datetime' is not defined

除此之外，还可以通过 in dir(builtins) 判断是否在dir列表中，来判断符号是否在内置命名空间 builtins 中。

>>> import builtins
>>> 'list' in [n for n in dir(builtins) if not n.startswith('_')]
True

或者尝试执行 help(list) 或 dir(list)，看是否正常输出从而判断是否包含在内置命名空间 builtins 中。

CLASSES

builtins 模块还提供了一些常用的基础类（CLASSES）：

CLASSES
    object
        BaseException

        bytearray
        bytes
        classmethod
        complex
        dict
        enumerate
        filter
        float
        frozenset
        int
            bool
        list
        map
        memoryview
        property
        range
        reversed
        set
        slice
        staticmethod
        str
        super
        tuple
        type
        zip

How do I check whether a module is installed or not in Python?

How to Check if a List, Tuple or Dictionary is Empty in Python

>>> str.__module__
'builtins'

>>> import inspect
>>> inspect.getmodule(str)
<module 'builtins' (built-in)>

str

Text Sequence Type — str

Textual data in Python is handled with str objects.

字符串类 str 是 python 最常用的类，用来处理文本数据。

字符串有三种定义方式：

• Single quotes: 'allows embedded "double" quotes'
• Double quotes: "allows embedded 'single' quotes"
• Triple quoted: '''Three single quotes''', """Three double quotes"""

Triple quoted strings may span multiple lines - all associated whitespace will be included in the string literal.

其中单引号定义的字符串中可携带双引号；双引号定义的字符串中可携带单引号。
若想以跨行模式定义长字符串，则可考虑使用三引号，支持换行书写。

---

两个相邻的字符串字面量会自动连接：

>>> str1='Py' 'thon'
>>> str1
'Python'

>>> prefix='Py'
>>> prefix+'thon'
'Python'

---

当书写长字符串时，使用 () 定义多个字面量部分，换行时自动跨行续接，直到反括号结束：

# 小括号定义多个字面量拼接
>>> text=('Put several strings within parentheses '
... 'to have them joined together.')
>>> text
'Put several strings within parentheses to have them joined together.'

# 三引号跨行书写长字符串
>>> text='''Put several strings within parentheses 
... to have them joined together.'''
>>> text
'Put several strings within parentheses \nto have them joined together.'

str[subscripted_index]：基于脚标索引访问指定位置的字符（位置对应长度为1的子串）。

Strings can be indexed (subscripted), with the first character having index 0. There is no separate character type; a character is simply a string of size one:

str[start:stop]：访问索引区间为 [start, stop) 对应的子字符串。

subscripted_index、start、stop 均可为负数，其中 -1 索引最后一个元素，依次类推。

Numeric Types

Numeric Types

• int：整形
• float：浮点型
• complex：复数

Binary Sequence Types

• bytes objects are immutable sequences of single bytes.
• bytearray objects are a mutable counterpart to bytes objects.

String and Bytes literals
Bytes and Bytearray Operations

Sequence Types

Sequence Types

list

列表 list 定义格式为：[e1, e2, e3, ...]

其中 e 可以为基本类型或 tuple、list、set、dict 等复合类型

# [整形,字符串,元组,列表,集合,字典]
>>> list1=[1,'2',(3,4),[5,6],{7,8},{'a':9,'b':10}]
>>> len(list1)
6

针对标量数值类型，可使用比 list 更高效的 array 类型（Efficient arrays of numeric values）。

Arrays are sequence types and behave very much like lists, except that the type of objects stored in them is constrained.

tuple

Tuples are immutable sequences, typically used to store collections of heterogeneous data.

元组 tuple 定义格式为：(e1, e2, e3, ...)

其中 e 可以为基本类型或 tuple、list、set、dict 等复合类型

# (整形,字符串,元组,列表,集合,字典)
>>> tuple1=(1,'2',(3,4),[5,6],{7,8},{'a':9,'b':10})
>>> len(tuple1)
6

内置函数 enumerate() 产生的结果为 list<tuple>，每个列表元素为 (index, value) 二元组（2-tuples）。

>>> help(enumerate)

Help on class enumerate in module builtins:

class enumerate(object)
 |  enumerate(iterable[, start]) -> iterator for index, value of iterable
 |  
 |  Return an enumerate object.  iterable must be another object that supports iteration.  The enumerate object yields pairs containing a count (from start, which defaults to zero) and a value yielded by the iterable argument.
 |  enumerate is useful for obtaining an indexed list:
 |      (0, seq[0]), (1, seq[1]), (2, seq[2]), ...

以下为具体示例：

>>> seasons = ['Spring', 'Summer', 'Fall', 'Winter']
>>> list(enumerate(seasons))
[(0, 'Spring'), (1, 'Summer'), (2, 'Fall'), (3, 'Winter')]

range

range 定义了区间范围。

The arguments to the range constructor must be integers (either built-in int or any object that implements the __index__ special method).

• class range(stop)
• class range(start, stop[, step])

定义前开后闭区间 start ≤ e ＜ stop，步进为 step。

start 默认为0；step 默认为1。

>>> list(range(10))
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

>>> list(range(1, 11))
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

>>> list(range(0, 30, 5))
[0, 5, 10, 15, 20, 25]

range(start,stop,step) 可用 while 循环等效实现：

>>> start=0
>>> stop=30
>>> step=5

>>> r=range(start,stop,step)
>>> list(r)
[0, 5, 10, 15, 20, 25]

# range 的等效定义
>>> i=0
>>> v=0
>>> while True:
...     v = start+i*step
...     if v >= stop:
...         break
...     else:
...         print('v[%d] = %d' % (i, v))
...         i += 1
... 
v[0] = 0
v[1] = 5
v[2] = 10
v[3] = 15
v[4] = 20
v[5] = 25

典型应用是 stop 取 len(list)，基于索引循环遍历列表：

>>> for i in range(len(list1)):\
...     print(list1[i])
... 
1
2
(3, 4)
[5, 6]
{8, 7}
{'a': 9, 'b': 10}

Set Types

Set Types — set, frozenset

• set：无序集合

A set object is an unordered collection of distinct hashable objects.

集合定义格式为：{e1, e2, e3, ...}

其中 e 可以为基本类型或 tuple 类型

>>> set1={1,'2',(3,4)}
>>> len(set1)
3

set 中的元素必须提供 __hash__() 方法，为 hashable（has a hash value），否则报错 TypeError: unhashable type:

>>> set2={1,'2',(3,4),[5,6]}
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'list'
>>> set3={1,'2',(3,4),{7,8}}
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'set'
>>> set4={1,'2',(3,4),{'a':9,'b':10}}
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'dict'

更多容器相关的类型，可参考 collections。

Mapping Types

Mapping Types — dict

• dict：无序字典(键值对映射)

A mapping object maps hashable values to arbitrary objects. Mappings are mutable objects. There is currently only one standard mapping type, the dictionary.
A dictionary's keys are almost arbitrary values. Values that are not hashable, that is, values containing lists, dictionaries or other mutable types may not be used as keys.

• key 必须为 arbitrary（hashable），list、set、dict 等 unhashable 类型不能作为键；
• value 可为 not hashable 或 hashable。

>>> dict1[squares]=3
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'list'
>>> dict1[3]=squares
>>> dict1
{3: [1, 4, 9, 16, 25]}

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