Python全栈之路----函数----内置方法

Built-in Functions
abs()	dict()	help()	min()	setattr()
all()	dir()	hex()	next()	slice()
any()	divmod()	id()	object()	sorted()
ascii()	enumerate()	input()	oct()	staticmethod()
bin()	eval()	int()	open()	str()
bool()	exec()	isinstance()	ord()	sum()
bytearray()	filter()	insubclass()	pow()	super()
bytes()	float()	iter()	print()	tuple()
callable()	format()	len()	property()	type()
chr()	frozenset()	list()	range()	vars()
classmethod()	getattr()	locals()	repr()	zip()
compile()	globals()	map()	reversed()	_import_()
complex()	hasattr()	max()	round()
delattr()	hash()	memoryview()	set()

• abs()  取绝对值
• dict()  把一个数据转成字典
• help()  帮助
• min()  从列表中取出最小数

>>> a  = [1,4,5,-1,3]
>>> min(a)
-1

• max()  从列表中取出最大数

>>> a  = [1,4,5,-1,3]
>>> max(a)
5

• all()  如果bool(x)为True，即x中所有元素均为True，all(x)为True。如果x是可循环的（列表为可循环的），all(x)也返回True。

空列表或列表内元素全为True，all()为True。

#一种特殊情况
>>> bool([])
False
>>> all([])
True

• any()

#和all相反，只要有列表中有一个元素为True，any即为True
>>> any([False,0])
False
>>> any([False,0,1])
True
>>> any([])
False

• dir()  打印当前程序中存在的所有变量

>>> dir()
['__annotations__', '__builtins__', '__doc__', '__loader__', '__name__', '__package__', '__spec__']  #系统自带变量
>>> dir(__builtins__)   #打印所有的内置模块
['ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException', 'BlockingIOError', 'BrokenPipeError', 'BufferError', 'BytesWarning', 'ChildProcessError', 'ConnectionAbortedError', 'ConnectionError', 'ConnectionRefusedError', 'ConnectionResetError', 'DeprecationWarning', 'EOFError', 'Ellipsis', 'EnvironmentError', 'Exception', 'False', 'FileExistsError', 'FileNotFoundError', 'FloatingPointError', 'FutureWarning', 'GeneratorExit', 'IOError', 'ImportError', 'ImportWarning', 'IndentationError', 'IndexError', 'InterruptedError', 'IsADirectoryError', 'KeyError', 'KeyboardInterrupt', 'LookupError', 'MemoryError', 'ModuleNotFoundError', 'NameError', 'None', 'NotADirectoryError', 'NotImplemented', 'NotImplementedError', 'OSError', 'OverflowError', 'PendingDeprecationWarning', 'PermissionError', 'ProcessLookupError', 'RecursionError', 'ReferenceError', 'ResourceWarning', 'RuntimeError', 'RuntimeWarning', 'StopAsyncIteration', 'StopIteration', 'SyntaxError', 'SyntaxWarning', 'SystemError', 'SystemExit', 'TabError', 'TimeoutError', 'True', 'TypeError', 'UnboundLocalError', 'UnicodeDecodeError', 'UnicodeEncodeError', 'UnicodeError', 'UnicodeTranslateError', 'UnicodeWarning', 'UserWarning', 'ValueError', 'Warning', 'WindowsError', 'ZeroDivisionError', '_', '__build_class__', '__debug__', '__doc__', '__import__', '__loader__', '__name__', '__package__', '__spec__', 'abs', 'all', 'any', 'ascii', 'bin', 'bool', 'breakpoint', 'bytearray', 'bytes', 'callable', 'chr', 'classmethod', 'compile', 'complex', 'copyright', 'credits', 'delattr', 'dict', 'dir', 'divmod', 'enumerate', 'eval', 'exec', 'exit', 'filter', 'float', 'format', 'frozenset', 'getattr', 'globals', 'hasattr', 'hash', 'help', 'hex', 'id', 'input', 'int', 'isinstance', 'issubclass', 'iter', 'len', 'license', 'list', 'locals', 'map', 'max', 'memoryview', 'min', 'next', 'object', 'oct', 'open', 'ord', 'pow', 'print', 'property', 'quit', 'range', 'repr', 'reversed', 'round', 'set', 'setattr', 'slice', 'sorted', 'staticmethod', 'str', 'sum', 'super', 'tuple', 'type', 'vars', 'zip']

• vars()  打印当前所有变量名及其对应的值

>>> vars()
{'__name__': '__main__', '__doc__': None, '__package__': None, '__loader__': <class '_frozen_importlib.BuiltinImporter'>, '__spec__': None, '__annotations__': {}, '__builtins__': <module 'builtins' (built-in)>, 's': frozenset({2, 3, 4, 5}), 'f': <function f at 0x000002C11182F7B8>, 'lis': [1, 2, 3]}

• locals()  在函数里面运行，打印函数里所有的局部变量名及其值

>>> def f():
...     n = 3
...     print(locals())
...
>>> f()
{'n': 3}

• globals()  打印所有全局变量名及其值

>>> globals()
{'__name__': '__main__', '__doc__': None, '__package__': None, '__loader__': <class '_frozen_importlib.BuiltinImporter'>, '__spec__': None, '__annotations__': {}, '__builtins__': <module 'builtins' (built-in)>, 's': frozenset({2, 3, 4, 5}), 'f': <function f at 0x000002C1118359D8>, 'lis': [1, 2, 3]}

• hex()  将数字转换成十六进制
• slice()  切片：相当于提前定义好切片要求

>>> l = list(range(10))
>>> l
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> s = slice(1,7,2)
>>> s
slice(1, 7, 2)
>>> l[1:7:2]
[1, 3, 5]
>>> l[s]
[1, 3, 5]

• divmod()  取整除和余数

>>> 10//3
3
>>> 10/3
3.3333333333333335
>>> 10%3
1
>>> divmod(10,3)  #10除以3
(3, 1)  #返回（商，余数）

• id()  查内存地址
• sorted()  排序，默认由小到大

#列表排序，和sort功能一致
>>> l = list(range(10))
>>> l[4] = 99
>>> l
[0, 1, 2, 3, 99, 5, 6, 7, 8, 9]
>>> sorted(l)
[0, 1, 2, 3, 5, 6, 7, 8, 9, 99]
>>> l
[0, 1, 2, 3, 99, 5, 6, 7, 8, 9]
>>> l.sort()
>>> l
[0, 1, 2, 3, 5, 6, 7, 8, 9, 99]
#字典排序
>>> d = {}
>>> for i in range(20):
...     d[i] = i-50
...
>>> d #字典本身无序
{0: -50, 1: -49, 2: -48, 3: -47, 4: -46, 5: -45, 6: -44, 7: -43, 8: -42, 9: -41, 10: -40, 11: -39, 12: -38, 13: -37, 14: -36, 15: -35, 16: -34, 17: -33, 18: -32, 19: -31}
>>> d.items() #生成元组同样无序
dict_items([(0, -50), (1, -49), (2, -48), (3, -47), (4, -46), (5, -45), (6, -44), (7, -43), (8, -42), (9, -41), (10, -40), (11, -39), (12, -38), (13, -37), (14, -36), (15, -35), (16, -34), (17, -33), (18, -32), (19, -31)])
>>> sorted(d.items()) #默认从小到大排序
[(0, -50), (1, -49), (2, -48), (3, -47), (4, -46), (5, -45), (6, -44), (7, -43), (8, -42), (9, -41), (10, -40), (11, -39), (12, -38), (13, -37), (14, -36), (15, -35), (16, -34), (17, -33), (18, -32), (19, -31)]
>>> sorted(d.items(),key= lambda x:x[1]) #按照value值从小到大排序
[(0, -50), (1, -49), (2, -48), (3, -47), (4, -46), (5, -45), (6, -44), (7, -43), (8, -42), (9, -41), (10, -40), (11, -39), (12, -38), (13, -37), (14, -36), (15, -35), (16, -34), (17, -33), (18, -32), (19, -31)]
>>> d[0] = 399
>>> sorted(d.items(),key=lambda x:x[1]) #按照value值从小到大排序
[(1, -49), (2, -48), (3, -47), (4, -46), (5, -45), (6, -44), (7, -43), (8, -42), (9, -41), (10, -40), (11, -39), (12, -38), (13, -37), (14, -36), (15, -35), (16, -34), (17, -33), (18, -32), (19, -31), (0, 399)]
>>> sorted(d.items(),key=lambda x:x[1],reverse=True)  #按照value值从大到小排序
[(0, 399), (19, -31), (18, -32), (17, -33), (16, -34), (15, -35), (14, -36), (13, -37), (12, -38), (11, -39), (10, -40), (9, -41), (8, -42), (7, -43), (6, -44), (5, -45), (4, -46), (3, -47), (2, -48), (1, -49)]

• reversed()  和sorted()一样，不过是默认由大到小
• ascii()  返回unico编码

>>> s = 'abcd路飞'
>>> s
'abcd路飞'
>>> ascii(s)  #返回s的Unicode编码
"'abcd\\u8def\\u98de'"

• enumerate()  枚举，返回索引
• input()  输入
• oct()  转成八进制
• bin()  转成二进制
• eval()  按解释器的规则把单行字符串转成代码运行

#将字符串转换成公式进行运算
>>> s = '1+3/2'
>>> s
'1+3/2'
>>> eval(s)
2.5
#执行单行代码
>>> eval('print("hello world")')
hello world
#不能执行多行代码
>>> code = '''
... if 3>5 :
...     print('3 is bigger than 5')
... else:
...     print('dddd')
... '''
>>> code
"\nif 3>5 :\n\tprint('3 is bigger than 5')\nelse:\n\tprint('dddd')\n\n\n"
>>> eval(code)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<string>", line 2
    if 3>5 :
     ^
SyntaxError: invalid syntax

• exec()  能运行多行代码，但是没有返回值

#exec()能运行多行代码但无返回值
>>> code = '''
... def foo():
...     print('run foo')
...     return 1234
... foo()
... '''
>>> res = exec(code)
run foo
>>> print('res',res)
res None
#运行单行代码与eval()对比
>> res1 = eval("1+3+3")
>>> res2 = exec("1+3+3")
>>> print('res',res1,res2)
res 7 None

• int()  转换成整数类型
• open()  打开文件open(file='', mode='',encoding='')
• str()  转换成字符串类型
• bool()  判断True or False，只有0是False
• ord()  返回字符串在ASCII码里的值

>>> ord('a')
97

• chr()  返回ASCII码值对应的字符串

>>> chr(97)
'a'

• sum()

>>> a = [1,4,5,-1,3,0]
>>> a
[1, 4, 5, -1, 3, 0]
>>> sum(a)  #将列表中所有元素加起来求和
12

• bytearray()

1. 1. 一般用于修改长字符串，短字符串可改成列表然后进行修改。
   2. 可将字符串在原地址上修改，但字符串中修改的个别元素的地址会发生变化。

>>> s = 'abcd路飞'
>>> id(s)
1496733953552
>>> s = s.encode('gbk')
>>> s
b'abcd\xc2\xb7\xb7\xc9'
>>> s = bytearray(s) #字符串变成bytearray之后能修改
>>> s
bytearray(b'abcd\xc2\xb7\xb7\xc9')
>>> s[4]
194
>>> s[4] = 233
>>> s
bytearray(b'abcd\xe9\xb7\xb7\xc9')
>>> s = s.decode('gbk')
>>> s
'abcd榉飞'
>>> id(s)  #在原地址上修改
1496733953552

• map()

>>> map(lambda x:x*x,[1,2,3,4,5])
<map object at 0x0000015C7C561080>
>>> list(map(lambda x:x*x,[1,2,3,4,5]))
[1, 4, 9, 16, 25]

• filter()  过滤

>>> filter(lambda x:x>3,[1,2,3,4,5])  #筛选出满足lambda条件的元素
<filter object at 0x0000015C7C561048>
>>> list(filter(lambda x:x>3,[1,2,3,4,5]))
[4, 5]

• reduce()

>>> import functools
>>> functools.reduce(lambda x,y:x+y,[1,2,3,4,5,6,7,8]) #求和
36
>>> functools.reduce(lambda x,y:x*y,[1,2,3,4,5,6,7,8]) #求乘积
40320
>>> functools.reduce(lambda x,y:x+y,[1,2,3,4,5,6,7,8],3) #求和加上最后一项
39

• pow()  求次方   pow(a, b) = a**b
• bytes()  换成byte类型
• float()  换成浮点类型
• print()  打印   print(value, ..., sep=' ', end='\n', file=sys.stdout, flush=False)  flush以后会用到，这里先不讲

>>> s = 'hey, my name is alex\n, from Shanghai'
>>> print(s)
hey, my name is alex
, from Shanghai
>>> print(s,end='.')
hey, my name is alex
, from Shanghai.>>> #在最后会默认加一个\n
...
>>> print(s,end='|') #end是以什么结尾
hey, my name is alex
, from Shanghai|>>>
>>> print('haifeng','gangniang',sep='->') #sep是以什么连接两个字符串
haifeng->gangniang

#写入文件
msg = '又回到最初的原点'
f = open('print_tofile.txt', 'w')
print(msg, '记忆中你青涩的脸', sep='|', end='.', file=f)#不会在最后自带换行，重复本行命令，可连着写入

• tuple()  变成元组
• callable()  判断是否可调用

>>> def f():
...     pass
...
>>> callable(f) #带()，即是函数，就可调用，其余不可调用
True
>>> lis = [1,2,3]
>>> callable(lis)
False

• format()  格式化
• len()  获取长度
• type()  类型
• frozenset()  冷冻的集合，即为不可变的集合

>>> s = {1,2,3,4,5}
>>> s.discard(1)
>>> s
{2, 3, 4, 5}
>>> s = frozenset(s)
>>> s.discard(3)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'frozenset' object has no attribute 'discard'

• list()  列表
• range()  循环
• repr()   把变量值显示成字符串形式

>>> s
frozenset({2, 3, 4, 5})
>>> repr(s)
'frozenset({2, 3, 4, 5})'

• zip()  将两个列表元素一一对应生成元组，无对应元素的多余部分被舍弃

>>> a = [1,2,3,4,5]
>>> b = ['a','b','c']
>>> a
[1, 2, 3, 4, 5]
>>> b
['a', 'b', 'c']
>>> zip(a,b)
<zip object at 0x000002C1118C4FC8>
>>> list(zip(a,b))
[(1, 'a'), (2, 'b'), (3, 'c')]

• complex()  把数字变成复数

>>> complex(3,5)
(3+5j)

• round()  保留几位小数，默认不保留小数部分

>>> round(1.234567)
1
>>> round(1.234567,2)
1.23

• hash()  把字符串变成数字

#只要不重启，数字不会重复
>>> hash('abcd')
6166213067681790707
>>> hash('abcd')
6166213067681790707

• set()  把列表变成集合

>>> set([1,2,3,4])
{1, 2, 3, 4}

后面讲模块会讲到：_import_()

后面面向对象再讲：next()  object()  staticmethod()  isinstance()  property()  classmethod()

delattr()  hasattr()  getattr()  setattr()  四剑客放在后面一起讲

memoryview()  基本用不到，用于大数据处理

compile()  编译代码用，现在用不到，讲模板引擎的时候可能会用到