Python_常见内置函数

Posted 2021-03-03 shz-blog

1. 方法

 注：class（类）是具有相同的属性和方法的对象的集合。

2. 例子

 （1）数据/集合类型

• str(object=‘‘); str(object=b‘‘, encoding=‘utf-8‘, errors=‘strict‘)
• int(x, base=10)
• float(x=0)
• complex(real=0, imag=0)

 1 >>> str(123)
 2 ‘123‘
 3 >>> str([‘a‘, ‘b‘, ‘c‘])
 4 "[‘a‘, ‘b‘, ‘c‘]"
 5 >>> str(123).join([‘a‘, ‘b‘, ‘c‘])
 6 ‘a123b123c‘
 7 >>> int(‘123‘)
 8 123
 9 >>> float(‘123‘)
10 123.0
11 >>> (0.75).as_integer_ratio()
12 (3, 4)
13 >>> (1.0).is_integer()
14 True
15 >>> complex(1, 2)
16 (1+2j)
17 >>> complex(1, 2).conjugate()
18 (1-2j)

注：str方法，详情见https://www.cnblogs.com/shz-blog/p/12426630.html

• range(stop), range(start, stop[, step])
• tuple(iterable=())
• list([iterable])
• dict(); dict(mapping); dict(iterable); dict(**kwargs)

 1 >>> r = range(40, 1, -3)
 2 >>> t = tuple(r)
 3 >>> l = list(r)
 4 >>> t
 5 (40, 37, 34, 31, 28, 25, 22, 19, 16, 13, 10, 7, 4)
 6 >>> l
 7 [40, 37, 34, 31, 28, 25, 22, 19, 16, 13, 10, 7, 4]
 8 >>> r.count(1)
 9 0
10 >>> r.index(31)
11 3
12 >>> t.count(10)
13 1
14 >>> t.index(31)
15 3
16 >>> l.sort()
17 >>> l
18 [4, 7, 10, 13, 16, 19, 22, 25, 28, 31, 34, 37, 40]
19 >>> dict(a=1, b=2, c=3)
20 {‘a‘: 1, ‘b‘: 2, ‘c‘: 3}
21 >>> dict(zip(list(‘abc‘), [1, 2, 3]))
22 {‘a‘: 1, ‘b‘: 2, ‘c‘: 3}
23 >>> dict([(‘a‘, 1), (‘b‘, 2), (‘c‘, 3)])
24 {‘a‘: 1, ‘b‘: 2, ‘c‘: 3}
25 >>> dict(a=1, b=2, c=3).items()
26 dict_items([(‘a‘, 1), (‘b‘, 2), (‘c‘, 3)])

注：list方法，详情见https://www.cnblogs.com/shz-blog/p/12438954.html；

　   dict方法，详情见https://www.cnblogs.com/shz-blog/p/12456194.html

• set([iterable])
• frozenset([iterable])

 1 >>> s1 = set(‘hello‘)
 2 >>> s1
 3 {‘o‘, ‘h‘, ‘e‘, ‘l‘}
 4 >>> s1.add(123)
 5 >>> s1
 6 {‘o‘, ‘l‘, ‘h‘, ‘e‘, 123}
 7 >>> s1.discard(‘o‘)
 8 >>> s1
 9 {‘l‘, ‘h‘, ‘e‘, 123}
10 >>> s2 = set(‘lemon‘)
11 >>> s2
12 {‘o‘, ‘l‘, ‘e‘, ‘m‘, ‘n‘}
13 >>> s1.update(s2)
14 >>> s1
15 {‘o‘, ‘l‘, ‘h‘, ‘e‘, ‘m‘, ‘n‘, 123}

 1 >>> a = frozenset(‘hello world‘)
 2 >>> a
 3 frozenset({‘w‘, ‘l‘, ‘ ‘, ‘r‘, ‘o‘, ‘h‘, ‘d‘, ‘e‘})
 4 >>> b = frozenset(range(5))
 5 >>> b
 6 frozenset({0, 1, 2, 3, 4})
 7 >>> c = frozenset(range(2,7))
 8 >>> c
 9 frozenset({2, 3, 4, 5, 6})
10 >>> b.union(c)    # 并集
11 frozenset({0, 1, 2, 3, 4, 5, 6})
12 >>> b.intersection(c)    # 交集
13 frozenset({2, 3, 4})
14 >>> b.difference(c)    # 差集
15 frozenset({0, 1})
16 >>> c.difference(b)    # 差集
17 frozenset({5, 6})
18 >>> b.symmetric_difference(c)    # 对称差集
19 frozenset({0, 1, 5, 6})
20 >>> b.isdisjoint(c)    # 是否没有交集
21 False
22 >>> d = frozenset(range(2,5))
23 >>> d
24 frozenset({2, 3, 4})
25 >>> d.issubset(b)    # 是否被包含
26 True
27 >>> b.issuperset(d)    # 是否包含
28 True
29 >>> e = d.copy()    #复制
30 >>> id(d) == id(e)
31 True

•  bytearray和bytes

 1 >>> bytes()
 2 b‘‘
 3 >>> bytes(3)
 4 b‘x00x00x00‘
 5 >>> bytes(‘abc‘, ‘utf-8‘)
 6 b‘abc‘
 7 >>> bytes([1, 2, 3])
 8 b‘x01x02x03‘
 9 >>> b‘abcd‘.replace(b‘bc‘, b‘XY‘)
10 b‘aXYd‘
11 
12 >>> B = b‘abc‘
13 >>> BA = bytearray(B)
14 >>> BA
15 bytearray(b‘abc‘)
16 >>> [i for i in B]
17 [97, 98, 99]
18 >>> [i for i in BA]
19 [97, 98, 99]
20 >>> B[0] = 65
21 Traceback (most recent call last):
22   File "<pyshell#25>", line 1, in <module>
23     B[0] = 65
24 TypeError: ‘bytes‘ object does not support item assignment
25 >>> BA[0] = 65
26 >>> BA
27 bytearray(b‘Abc‘)

（2）操作

• format(value, format_spec=‘‘)

　　详情见https://www.cnblogs.com/shz-blog/p/12422194.html

• len(obj)
• sorted(iterable, key=None, reverse=False)
• reversed(sequence)
• slice(stop); slice(start, stop[, step])

 1 >>> L = list(‘abcde‘)
 2 >>> L
 3 [‘a‘, ‘b‘, ‘c‘, ‘d‘, ‘e‘]
 4 >>> len(L)
 5 5
 6 >>> sorted(L, reverse=True)
 7 [‘e‘, ‘d‘, ‘c‘, ‘b‘, ‘a‘]
 8 >>> list(reversed(L))
 9 [‘e‘, ‘d‘, ‘c‘, ‘b‘, ‘a‘]
10 >>> L[slice(1, 4, 2)]
11 [‘b‘, ‘d‘]

• enumerate(iterable, start=0)
• zip(iter1 [,iter2 [...]])
• map(func, *iterables)

 1 >>> l1 = [1, 2, 3]
 2 >>> l2 = [4, 5, 6]
 3 >>> l3 = [7, 8, 9, 10]
 4 
 5 >>> list(enumerate(l3))
 6 [(0, 7), (1, 8), (2, 9), (3, 10)]
 7 
 8 >>> list(zip(l1, l2))
 9 [(1, 4), (2, 5), (3, 6)]
10 >>> list(zip(l1, l3))
11 [(1, 7), (2, 8), (3, 9)]
12 >>> list(zip(*zip(l1, l3)))    # *理解为解压
13 [(1, 2, 3), (7, 8, 9)]
14 
15 >>> list(map(lambda x: x * 3, l1))
16 [3, 6, 9]
17 >>> list(map(lambda x, y: x + y, l1, l2))
18 [5, 7, 9]

（3）输入输出

•  input(prompt=None)
• open(file, mode=‘r‘, buffering=-1, encoding=None, errors=None, newline=None, closefd=True, opener=None)
• print(value, ..., sep=‘ ‘, end=‘ ‘, file=sys.stdout, flush=False)

1 >>> age = input(‘请输入年龄:‘)
2 请输入年龄:18
3 >>> age
4 ‘18‘
5 >>> type(age)
6 <class ‘str‘>

 注：open的用法，详情见https://www.cnblogs.com/sesshoumaru/p/6047046.html；

        文件的打开、读取等各种操作，详情见https://www.cnblogs.com/hackpig/p/8215786.html

1 >>> print(‘hello world‘, ‘hello Bunny‘, sep=‘
‘, end=‘_‘*10)
2 hello world
3 hello Bunny__________

注：flush的用法，参考https://blog.csdn.net/Zhongjie1986/article/details/91890109

（4）数学函数

• abs(x)
• divmod(x, y)
• pow(x, y, z=None)
• round(number, ndigits=None)
• sum(iterable, start=0)
• max(arg1, arg2, *args, *[, key=func]); max(iterable, *[, default=obj, key=func])
• min(arg1, arg2, *args, *[, key=func]); min(iterable, *[, default=obj, key=func])

 1 >>> abs(-10)
 2 10
 3 >>> divmod(11, 3)
 4 (3, 2)
 5 >>> pow(2, 3)
 6 8
 7 >>> pow(2, 3, 3)
 8 2
 9 >>> round(1.2345, 2)
10 1.23
11 >>> sum(range(5))
12 10

 1 >>> max(1, 2, 3)
 2 3
 3 >>> max(1, 2, ‘3‘)
 4 Traceback (most recent call last):
 5   File "<pyshell#1>", line 1, in <module>
 6     max(1, 2, ‘3‘)
 7 TypeError: ‘>‘ not supported between instances of ‘str‘ and ‘int‘
 8 >>> max(1, 2, ‘3‘, key=int)
 9 ‘3‘
10 >>> max(-3, 1, 2, key=abs)
11 -3
12 >>> max(‘123‘)
13 ‘3‘
14 >>> max([1, 8], [2, 6], [3, 4])
15 [3, 4]
16 >>> couple = ({‘name‘: ‘Bunny‘, ‘age‘: 18, ‘salary‘: 888}, {‘name‘: ‘Twan‘, ‘age‘: 20, ‘salary‘: 666})
17 >>> max(couple, key=lambda x: x[‘age‘])
18 {‘name‘: ‘Twan‘, ‘age‘: 20, ‘salary‘: 666}
19 >>> max((), default=0)
20 0

 （5）编码

• bin(number), oct(number), hex(number)
• chr(i), ord(c), ascii(obj), repr(obj)

 1 >>> bin(10)
 2 ‘0b1010‘
 3 >>> oct(10)
 4 ‘0o12‘
 5 >>> hex(10)
 6 ‘0xa‘
 7 >>> chr(65)
 8 ‘A‘
 9 >>> ord(‘A‘)
10 65
11 >>> ascii(‘hello world‘)
12 "‘hello world‘"
13 >>> repr(‘hello world‘)
14 "‘hello world‘"
15 >>> ascii(‘你好，世界‘)
16 "‘u4f60u597duff0cu4e16u754c‘"
17 >>> repr(‘你好，世界‘)
18 "‘你好，世界‘"

（6）判断

• bool(x), all(iterable), any(iterable), callable(object)

 1 >>> all([‘a‘, ‘b‘, ‘c‘])
 2 True
 3 >>> all([‘a‘, ‘b‘, ‘‘, ‘c‘])
 4 False
 5 >>> all([])
 6 True
 7 >>> any([0, ‘‘, False])
 8 False
 9 >>> any([])
10 False
11 >>> callable(str)
12 True
13 >>> callable(‘hello world‘)
14 False

（7）迭代器

• iter(iterable); iter(callable, sentinel)
• next(iterator[, default])
• filter(function or None, iterable)

 1 >>> for i in iter(list(‘abc‘)):
 2     　　print(i)
 3     
 4 a
 5 b
 6 c
 7 
 8 >>> from random import randint
 9 >>> def guess():
10     return randint(0,10)
11 >>> num = 1
12 >>> for i in iter(guess, 5):
13     print(‘第%s次猜测，猜测数字为：%s‘ % (num, i))
14     num += 1
15     
16 第1次猜测，猜测数字为：3
17 第2次猜测，猜测数字为：1

注：猜数字的例子来自http://www.imooc.com/article/287997

 1 >>> i = iter(list(‘abc‘))
 2 >>> next(i)
 3 ‘a‘
 4 >>> next(i)
 5 ‘b‘
 6 >>> next(i)
 7 ‘c‘
 8 >>> next(i)
 9 Traceback (most recent call last):
10   File "<pyshell#27>", line 1, in <module>
11     next(i)
12 StopIteration
13 >>> next(i, 0)
14 0

1 >>> def is_odd(n):
2     return n % 2 == 1
3 
4 >>> oldlist = [i for i in range(1,11)]
5 >>> oldlist
6 [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
7 >>> newlist = list(filter(is_odd, oldlist))
8 >>> newlist
9 [1, 3, 5, 7, 9]

 （8）属性操作

• getattr(obj, name[, default])
• setattr(obj, name, value)
• hasattr(obj, name)
• delattr(obj, name)

 1 >>> class Person:
 2     　　name = ‘Bunny‘
 3     　　age = 18
 4     　　sex = ‘女‘
 5 
 6 >>> Person.name
 7 ‘Bunny‘
 8 >>> Person.country
 9 Traceback (most recent call last):
10   File "<pyshell#6>", line 1, in <module>
11     Person.country
12 AttributeError: type object ‘Person‘ has no attribute ‘country‘
13 >>> getattr(Person, ‘age‘, 0)
14 18
15 >>> getattr(Person, ‘country‘, 0)
16 0
17 >>> setattr(Person, ‘country‘, ‘China‘)
18 >>> getattr(Person, ‘country‘, 0)
19 ‘China‘
20 >>> delattr(Person, ‘sex‘)
21 >>> hasattr(Person, ‘sex‘)
22 False

（9）辅助函数

• dir([object])

1 >>> dir()
2 [‘__annotations__‘, ‘__builtins__‘, ‘__doc__‘, ‘__loader__‘, ‘__name__‘, ‘__package__‘, ‘__spec__‘]
3 >>> dir(dict)
4 [‘__class__‘, ‘__contains__‘, ‘__delattr__‘, ‘__delitem__‘, ‘__dir__‘, ‘__doc__‘, ‘__eq__‘, ‘__format__‘, ‘__ge__‘, ‘__getattribute__‘, ‘__getitem__‘, ‘__gt__‘, ‘__hash__‘, ‘__init__‘, ‘__init_subclass__‘, ‘__iter__‘, ‘__le__‘, ‘__len__‘, ‘__lt__‘, ‘__ne__‘, ‘__new__‘, ‘__reduce__‘, ‘__reduce_ex__‘, ‘__repr__‘, ‘__setattr__‘, ‘__setitem__‘, ‘__sizeof__‘, ‘__str__‘, ‘__subclasshook__‘, ‘clear‘, ‘copy‘, ‘fromkeys‘, ‘get‘, ‘items‘, ‘keys‘, ‘pop‘, ‘popitem‘, ‘setdefault‘, ‘update‘, ‘values‘]

• help([object])

1 >>> help(hash)
2 Help on built-in function hash in module builtins:
3 
4 hash(obj, /)
5     Return the hash value for the given object.
6     
7     Two objects that compare equal must also have the same hash value, but the
8     reverse is not necessarily true.

•  hash(obj)

1 >>> hash(‘hello world‘)
2 -8331809543453374991
3 >>> hash(tuple(‘abcde‘))
4 5996617995451668254

　　哈希的相关知识点：https://www.cnblogs.com/abdm-989/p/11329122.html

• id([object])

1 >>> a = ‘hello world‘
2 >>> b = a
3 >>> id(a)
4 1873301041520
5 >>> id(b)
6 1873301041520

• memoryview(object)

1 >>> a = memoryview(bytearray(‘abcde‘, ‘utf-8‘))
2 >>> a[1]
3 98
4 >>> a[1:3]
5 <memory at 0x0000017F63B83408>
6 >>> a[1:3].tobytes()
7 b‘bc‘
8 >>> a[1:3].tolist()
9 [98, 99]

优点：memoryview减少内存拷贝，优化效率（详情可参考https://www.hustyx.com/python/222/）

• type(object), type(name, bases, dict)
• issubclass(cls, class_or_tuple)
• isinstance(obj, class_or_tuple)

1 >>> a = 2
2 >>> type(a)
3 <class ‘int‘>
4 >>> isinstance(a, int)
5 True
6 >>> isinstance(a, str)
7 False
8 >>> isinstance(a, (str, int, list))    # 是元组中的一个就返回True
9 True

 1 >>> class A:
 2　　　　pass
 3 
 4 >>> class B(A):
 5　　　　pass
 6 
 7 >>> issubclass(B, A)
 8 True
 9 >>> isinstance(B(), A)
10 True
11 >>> type(B()) == A
12 False

（10）面向对象

• @classmethod, @staticmethod

 1 >>> class A:
 2     num = 0    #类属性
 3     #类方法
 4     @classmethod
 5     def setNum(cls,newNum):
 6         cls.num = newNum
 7     #实例方法
 8     def __init__(self):
 9         self.age = 1    #实例属性
10     def setAge(self, newAge):
11         self.age = newAge
12     #静态方法
13     @staticmethod
14     def printInfo():
15         print(‘类方法修改类属性，实例方法修改实例属性，静态方法不访问类‘)
16 
17         
18 >>> a = A()
19 >>> a.setAge(18)
20 >>> a.age
21 18
22 >>> A.setAge(18)
23 Traceback (most recent call last):
24   File "<pyshell#21>", line 1, in <module>
25     A.setAge(18)
26 TypeError: setAge() missing 1 required positional argument: ‘newAge‘
27 >>> A.setNum(100)
28 >>> A.num
29 100
30 >>> A.printInfo()
31 类方法修改类属性，实例方法修改实例属性，静态方法不访问类

• property(fget=None, fset=None, fdel=None, doc=None); @property

效果：

 1 >>> c = C()
 2 >>> c.x = 10
 3 >>> c.x
 4 10
 5 >>> del c.x
 6 >>> c.x
 7 Traceback (most recent call last):
 8   File "<pyshell#18>", line 1, in <module>
 9     c.x
10   File "<pyshell#13>", line 5, in x
11     return self._x
12 AttributeError: ‘C‘ object has no attribute ‘_x‘

方式1：

 1 >>> class C(object):
 2     　　def getx(self): return self._x
 3     　　def setx(self, value): self._x = value
 4     　　def delx(self): del self._x
 5     　　x = property(getx, setx, delx, "I‘m the ‘x‘ property.")

方式2：

 1 >>> class C(object):
 2     　　@property
 3     　　def x(self):
 4         　　"I am the ‘x‘ property."
 5         　　return self._x
 6     　　@x.setter
 7     　　def x(self, value):
 8         　　self._x = value
 9     　　@x.deleter
10     　　def x(self):
11         　　del self._x

•  super

 1 >>> class A:
 2     def add(self, x):
 3         print(x+1)
 4         
 5 >>> class B(A):
 6     def add(self, x):
 7         super().add(x)
 8         
 9 >>> B().add(2)
10 3

•  globals, locals, vars([object])

 1 >>> word = ‘hello world‘
 2 >>> def test(x):
 3     y = 1
 4     print(locals())
 5 
 6 >>> test(2)
 7 {‘x‘: 2, ‘y‘: 1}
 8 >>> globals()
 9 {‘__name__‘: ‘__main__‘, ‘__doc__‘: None, ‘__package__‘: None, ‘__loader__‘: <class ‘_frozen_importlib.BuiltinImporter‘>, ‘__spec__‘: None, ‘__annotations__‘: {}, ‘__builtins__‘: <module ‘builtins‘ (built-in)>, ‘word‘: ‘hello world‘, ‘test‘: <function test at 0x0000023BE4CEEF28>}
10 >>> class A:
11     a = 1
12 
13 >>> vars(A)
14 mappingproxy({‘__module__‘: ‘__main__‘, ‘a‘: 1, ‘__dict__‘: <attribute ‘__dict__‘ of ‘A‘ objects>, ‘__weakref__‘: <attribute ‘__weakref__‘ of ‘A‘ objects>, ‘__doc__‘: None})

（11）可执行对象

• eval(source, globals=None, locals=None)
• exec(source, globals=None, locals=None)
• compile(source, filename, mode, flags=0, dont_inherit=False, optimize=-1)

 1 >>> eval(‘2 * 3 + 4‘)
 2 10
 3 >>> exec(‘print("hello world")‘)
 4 hello world
 5 >>> eval_code = compile(‘2 * 3 + 4‘, ‘‘, ‘eval‘)
 6 >>> eval_code
 7 <code object <module> at 0x00000269270686F0, file "", line 1>
 8 >>> eval(eval_code)
 9 10
10 >>> exec_code = compile(‘print("hello world")‘, ‘‘, ‘exec‘)
11 >>> exec_code
12 <code object <module> at 0x0000026927074150, file "", line 1>
13 >>> exec(exec_code)
14 hello world

 需要注意的是，exec函数和eval函数都是将用户提供的字符串作为代码执行，将无法控制代码的行为，会带来严重的安全隐患，使用的时候要慎重。

1 >>> exec(‘abs="xyz"‘)
2 >>> abs(-1)
3 Traceback (most recent call last):
4   File "<pyshell#13>", line 1, in <module>
5     abs(-1)
6 TypeError: ‘str‘ object is not callable

报错的原因是使用exec函数将‘xyz‘赋值给了abs，abs不再是求绝对值的函数了。为了避免污染命名空间，在调用exec函数时，可以给它传递第二个参数——命名空间。

1 >>> scope = {}
2 >>> exec(‘abs="xyz"‘, scope)
3 >>> abs(-1)
4 1
5 >>> scope[‘abs‘]
6 ‘xyz‘

注：参考了https://www.cnblogs.com/lucky-heng/p/10161190.html

 

题外话：关于内置函数，发现了一个非常详细的介绍（https://www.cnblogs.com/sesshoumaru/p/6140987.html），这个博主还对每个函数分别用一篇随笔来介绍。写到一半，看到这么详尽的博客，瞬间就有点不想写了，不过我写博客主要还是为了方便自己日后查阅，不够详细的地方可以移步上面这个博主。本文总体参考了官方说明文档、内置函数介绍英文版（https://docs.python.org/3/library/functions.html#classmethod）及其翻译版（http://www.beixiongxiong.com/course/bxx_bzk_02/2084/）。