id() 返回對(duì)象的唯一標(biāo)識(shí)
內(nèi)置函數(shù) id()舌涨，Python 官方文檔描述如下：
help(id)
Help on built-in function id in module builtins:
id(obj, /)
Return the identity of an object.
This is guaranteed to be unique among simultaneously existing objects.
(CPython uses the object's memory address.)
返回對(duì)象的唯一標(biāo)識(shí)卸勺。該標(biāo)識(shí)是一個(gè)整數(shù)致份，在此對(duì)象的生命周期中保證是唯一且恒定的崇裁。
CPython 中該標(biāo)識(shí)是對(duì)象的內(nèi)存地址逻族。
id(1), id(1.0)
(140736642126656, 2785998726512)
1 == 1.0
True
# 兩個(gè)變量引用了同一個(gè)值為 1 的對(duì)象
a = 1
b = int('01')
id(a), id(b)
(140736642126656, 140736642126656)
# 兩個(gè)值為 1000 的不同對(duì)象
a = 1000
b = 1000
id(a), id(b)
(2785998745552, 2785998745360)
# 可變對(duì)象改變值蜻底，還是同一個(gè)對(duì)象
_list = [1,2,3]
print(id(_list),_list)
del _list[:]
print(id(_list),_list)
2785999307336 [1, 2, 3]
2785999307336 []
input() 接受輸入返回字符串
內(nèi)置函數(shù) input()，Python 官方文檔描述如下：
help(input)
Help on method raw_input in module ipykernel.kernelbase:
raw_input(prompt='') method of ipykernel.ipkernel.IPythonKernel instance
Forward raw_input to frontends
Raises
------
StdinNotImplentedError if active frontend doesn't support stdin.
如果存在 prompt 實(shí)參聘鳞，則作為提示信息輸出薄辅。接下來，該函數(shù)將輸入轉(zhuǎn)換為字符串并返回搁痛。無輸入則返回空字符串长搀。
input('輸入提示：')
輸入提示： 1+1
'1+1'
input('輸入提示：')
輸入提示：
''
int 創(chuàng)建整數(shù)
內(nèi)置函數(shù)（類）int，Python 官方文檔描述如下：
help(int)
Help on class int in module builtins:
class int(object)
| int([x]) -> integer
| int(x, base=10) -> integer
|
| Convert a number or string to an integer, or return 0 if no arguments
| are given. If x is a number, return x.__int__(). For floating point
| numbers, this truncates towards zero.
|
| If x is not a number or if base is given, then x must be a string,
| bytes, or bytearray instance representing an integer literal in the
| given base. The literal can be preceded by '+' or '-' and be surrounded
| by whitespace. The base defaults to 10\. Valid bases are 0 and 2-36.
| Base 0 means to interpret the base from the string as an integer literal.
| >>> int('0b100', base=0)
| 4
|
| Built-in subclasses:
| bool
|
| Methods defined here:
|
| __abs__(self, /)
| abs(self)
|
| __add__(self, value, /)
| Return self+value.
|
| __and__(self, value, /)
| Return self&value.
|
| __bool__(self, /)
| self != 0
|
| __ceil__(...)
| Ceiling of an Integral returns itself.
|
| __divmod__(self, value, /)
| Return divmod(self, value).
|
| __eq__(self, value, /)
| Return self==value.
|
| __float__(self, /)
| float(self)
|
| __floor__(...)
| Flooring an Integral returns itself.
|
| __floordiv__(self, value, /)
| Return self//value.
|
| __format__(self, format_spec, /)
| Default object formatter.
|
| __ge__(self, value, /)
| Return self>=value.
|
| __getattribute__(self, name, /)
| Return getattr(self, name).
|
| __getnewargs__(self, /)
|
| __gt__(self, value, /)
| Return self>value.
|
| __hash__(self, /)
| Return hash(self).
|
| __index__(self, /)
| Return self converted to an integer, if self is suitable for use as an index into a list.
|
| __int__(self, /)
| int(self)
|
| __invert__(self, /)
| ~self
|
| __le__(self, value, /)
| Return self<=value.
|
| __lshift__(self, value, /)
| Return self<<value.
|
| __lt__(self, value, /)
| Return self<value.
|
| __mod__(self, value, /)
| Return self%value.
|
| __mul__(self, value, /)
| Return self*value.
|
| __ne__(self, value, /)
| Return self!=value.
|
| __neg__(self, /)
| -self
|
| __or__(self, value, /)
| Return self|value.
|
| __pos__(self, /)
| +self
|
| __pow__(self, value, mod=None, /)
| Return pow(self, value, mod).
|
| __radd__(self, value, /)
| Return value+self.
|
| __rand__(self, value, /)
| Return value&self.
|
| __rdivmod__(self, value, /)
| Return divmod(value, self).
|
| __repr__(self, /)
| Return repr(self).
|
| __rfloordiv__(self, value, /)
| Return value//self.
|
| __rlshift__(self, value, /)
| Return value<<self.
|
| __rmod__(self, value, /)
| Return value%self.
|
| __rmul__(self, value, /)
| Return value*self.
|
| __ror__(self, value, /)
| Return value|self.
|
| __round__(...)
| Rounding an Integral returns itself.
| Rounding with an ndigits argument also returns an integer.
|
| __rpow__(self, value, mod=None, /)
| Return pow(value, self, mod).
|
| __rrshift__(self, value, /)
| Return value>>self.
|
| __rshift__(self, value, /)
| Return self>>value.
|
| __rsub__(self, value, /)
| Return value-self.
|
| __rtruediv__(self, value, /)
| Return value/self.
|
| __rxor__(self, value, /)
| Return value^self.
|
| __sizeof__(self, /)
| Returns size in memory, in bytes.
|
| __sub__(self, value, /)
| Return self-value.
|
| __truediv__(self, value, /)
| Return self/value.
|
| __trunc__(...)
| Truncating an Integral returns itself.
|
| __xor__(self, value, /)
| Return self^value.
|
| as_integer_ratio(self, /)
| Return integer ratio.
|
| Return a pair of integers, whose ratio is exactly equal to the original int
| and with a positive denominator.
|
| >>> (10).as_integer_ratio()
| (10, 1)
| >>> (-10).as_integer_ratio()
| (-10, 1)
| >>> (0).as_integer_ratio()
| (0, 1)
|
| bit_length(self, /)
| Number of bits necessary to represent self in binary.
|
| >>> bin(37)
| '0b100101'
| >>> (37).bit_length()
| 6
|
| conjugate(...)
| Returns self, the complex conjugate of any int.
|
| to_bytes(self, /, length, byteorder, *, signed=False)
| Return an array of bytes representing an integer.
|
| length
| Length of bytes object to use. An OverflowError is raised if the
| integer is not representable with the given number of bytes.
| byteorder
| The byte order used to represent the integer. If byteorder is 'big',
| the most significant byte is at the beginning of the byte array. If
| byteorder is 'little', the most significant byte is at the end of the
| byte array. To request the native byte order of the host system, use
| `sys.byteorder' as the byte order value.
| signed
| Determines whether two's complement is used to represent the integer.
| If signed is False and a negative integer is given, an OverflowError
| is raised.
|
| ----------------------------------------------------------------------
| Class methods defined here:
|
| from_bytes(bytes, byteorder, *, signed=False) from builtins.type
| Return the integer represented by the given array of bytes.
|
| bytes
| Holds the array of bytes to convert. The argument must either
| support the buffer protocol or be an iterable object producing bytes.
| Bytes and bytearray are examples of built-in objects that support the
| buffer protocol.
| byteorder
| The byte order used to represent the integer. If byteorder is 'big',
| the most significant byte is at the beginning of the byte array. If
| byteorder is 'little', the most significant byte is at the end of the
| byte array. To request the native byte order of the host system, use
| `sys.byteorder' as the byte order value.
| signed
| Indicates whether two's complement is used to represent the integer.
|
| ----------------------------------------------------------------------
| Static methods defined here:
|
| __new__(*args, **kwargs) from builtins.type
| Create and return a new object. See help(type) for accurate signature.
|
| ----------------------------------------------------------------------
| Data descriptors defined here:
|
| denominator
| the denominator of a rational number in lowest terms
|
| imag
| the imaginary part of a complex number
|
| numerator
| the numerator of a rational number in lowest terms
|
| real
| the real part of a complex number
將一個(gè)數(shù)字鸡典，字符串或字節(jié)串轉(zhuǎn)換為整數(shù)源请。參數(shù)說明：
- 不給參數(shù)返回整數(shù) 0。
- 參數(shù) x 為數(shù)字時(shí)彻况，不能有參數(shù) base谁尸，且數(shù)字不能是復(fù)數(shù)。浮點(diǎn)數(shù)將取整纽甘。
- 參數(shù) x 為字符串或字節(jié)串良蛮，參數(shù) base 可選，默認(rèn)按十進(jìn)制轉(zhuǎn)換悍赢，否則按照 base 指定進(jìn)制轉(zhuǎn)換决瞳。
- base 取值范圍為 0 和 2~36货徙。
- base 取 0 將按照參數(shù) x 的字面量來精確解釋。取其他數(shù)字則需符合相應(yīng)進(jìn)制規(guī)則皮胡。
- 字符串或字節(jié)串不能是浮點(diǎn)數(shù)形式痴颊；前面可以有正負(fù)號(hào)；前后可以有空格屡贺，中間則不能有空格蠢棱。
type(int)
type
int()
0
int(3.18e01), int(10), int(0x10)
(31, 10, 16)
int(' -10 '), int(b' +10')
(-10, 10)
int('10',2), int('10',8), int('z',36)
(2, 8, 35)
int('001'), int('0b10',0)
(1, 2)
int('001',0) # 001 不是合法的整數(shù)
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
<ipython-input-12-1cf9048a8c3e> in <module>
----> 1 int('001',0)
ValueError: invalid literal for int() with base 0: '001'
int('9', 8) # 8 進(jìn)制沒有 9
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
<ipython-input-13-3558097bd025> in <module>
----> 1 int('9', 8)
ValueError: invalid literal for int() with base 8: '9'
int('3.14') # 不能是浮點(diǎn)數(shù)形式
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
<ipython-input-14-1456603af047> in <module>
----> 1 int('3.14')
ValueError: invalid literal for int() with base 10: '3.14'
isinstance() 是給定類的實(shí)例？
內(nèi)置函數(shù) isinstance()甩栈，Python 官方文檔描述如下：
help(isinstance)
Help on built-in function isinstance in module builtins:
isinstance(obj, class_or_tuple, /)
Return whether an object is an instance of a class or of a subclass thereof.
A tuple, as in ``isinstance(x, (A, B, ...))``, may be given as the target to
check against. This is equivalent to ``isinstance(x, A) or isinstance(x, B)
or ...`` etc.
如果對(duì)象 obj 是給定類的實(shí)例或者是其 (直接泻仙、間接或虛擬) 子類的實(shí)例則返回 True，不是則返回 False量没。給定的不是類則引發(fā) TypeError 異常玉转。
給定類可以以元組形式傳參，obj 是其中任何一個(gè)類型的實(shí)例就返回 True允蜈。
isinstance(1, int)
True
isinstance('abc', (float, complex))
False
# bool 是 int 的子類型冤吨，但不是實(shí)例
isinstance(bool, int)
False
# True 是 int 的子類的實(shí)例
isinstance(True, int)
True
# bool 的實(shí)例只有 True 和 False
isinstance(1, bool)
False
# 所有的對(duì)象都是 object 的實(shí)例
isinstance(object, object)
True
import random # 模塊
class A:pass # 自定義類
isinstance(1, object),\
isinstance(int, object),\
isinstance(list, object),\
isinstance(random, object),\
isinstance(A, object)
(True, True, True, True, True)
issubclass() 是給定類的子類嗎？
內(nèi)置函數(shù) issubclass()饶套，Python 官方文檔描述如下：
help(issubclass)
Help on built-in function issubclass in module builtins:
issubclass(cls, class_or_tuple, /)
Return whether 'cls' is a derived from another class or is the same class.
A tuple, as in ``issubclass(x, (A, B, ...))``, may be given as the target to
check against. This is equivalent to ``issubclass(x, A) or issubclass(x, B)
or ...`` etc.
如果類 cls 是給定類的 (直接、間接或虛擬) 子類則返回 True垒探，不是則返回 False妓蛮。給定的不是類則引發(fā) TypeError 異常。
給定類可以以元組形式傳參圾叼，cls 是其中任何一個(gè)類的子類就返回 True蛤克。
issubclass(1, int) # 1 不是類
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-2-257e7a8dbb04> in <module>
----> 1 issubclass(1, int)
TypeError: issubclass() arg 1 must be a class
issubclass(bool, int)
True
issubclass(bool, (set, str, list))
False
# 所有的類都是 object 的子類
class A:pass
issubclass(A, object),\
issubclass(str, object),\
issubclass(object, object)
(True, True, True)
iter() 轉(zhuǎn)迭代器
內(nèi)置函數(shù) iter()，Python 官方文檔描述如下：
help(iter)
Help on built-in function iter in module builtins:
iter(...)
iter(iterable) -> iterator
iter(callable, sentinel) -> iterator
Get an iterator from an object. In the first form, the argument must
supply its own iterator, or be a sequence.
In the second form, the callable is called until it returns the sentinel.
將一個(gè)可迭代對(duì)象（iterable）或可調(diào)用對(duì)象（callable）轉(zhuǎn)換為一個(gè)迭代器夷蚊。
當(dāng)參數(shù)是可調(diào)用對(duì)象時(shí)构挤，需要提供參數(shù) sentinel，生成的迭代器惕鼓，每次
迭代時(shí)都會(huì)不帶實(shí)參地調(diào)用 callable筋现，返回 sentinel 時(shí)則觸
發(fā) StopIteration。
a = iter('abcd')
a
<str_iterator at 0x1c7eea4f910>
next(a),next(a),next(a),next(a)
('a', 'b', 'c', 'd')
a = iter(int, 1)
for i in range(3):
print(next(a))
0
0
0
a = iter(int, 0)
next(a)
---------------------------------------------------------------------------
StopIteration Traceback (most recent call last)
<ipython-input-21-694e44f6d78c> in <module>
1 a = iter(int, 0)
----> 2 next(a)
StopIteration:
len() 返回元素個(gè)數(shù)
內(nèi)置函數(shù) len()箱歧，Python 官方文檔描述如下：
help(len)
Help on built-in function len in module builtins:
len(obj, /)
Return the number of items in a container.
返回對(duì)象的長(zhǎng)度（元素個(gè)數(shù)）矾飞。實(shí)參可以是序列（如 str、bytes呀邢、tuple洒沦、list 或 range 等的實(shí)例），集合（set 或 frozenset 的實(shí)例）价淌，或字典（dict 的實(shí)例）等申眼。
len('123')
3
len('嗨')
1
len('嗨'.encode())
3
len([1,2,3])
3
len({'a':1,'b':2})
2
list 創(chuàng)建列表
內(nèi)置函數(shù)（類）list瞒津，Python 官方文檔描述如下：
help(list)
Help on class list in module builtins:
class list(object)
| list(iterable=(), /)
|
| Built-in mutable sequence.
|
| If no argument is given, the constructor creates a new empty list.
| The argument must be an iterable if specified.
|
| Methods defined here:
|
| __add__(self, value, /)
| Return self+value.
|
| __contains__(self, key, /)
| Return key in self.
|
| __delitem__(self, key, /)
| Delete self[key].
|
| __eq__(self, value, /)
| Return self==value.
|
| __ge__(self, value, /)
| Return self>=value.
|
| __getattribute__(self, name, /)
| Return getattr(self, name).
|
| __getitem__(...)
| x.__getitem__(y) <==> x[y]
|
| __gt__(self, value, /)
| Return self>value.
|
| __iadd__(self, value, /)
| Implement self+=value.
|
| __imul__(self, value, /)
| Implement self*=value.
|
| __init__(self, /, *args, **kwargs)
| Initialize self. See help(type(self)) for accurate signature.
|
| __iter__(self, /)
| Implement iter(self).
|
| __le__(self, value, /)
| Return self<=value.
|
| __len__(self, /)
| Return len(self).
|
| __lt__(self, value, /)
| Return self<value.
|
| __mul__(self, value, /)
| Return self*value.
|
| __ne__(self, value, /)
| Return self!=value.
|
| __repr__(self, /)
| Return repr(self).
|
| __reversed__(self, /)
| Return a reverse iterator over the list.
|
| __rmul__(self, value, /)
| Return value*self.
|
| __setitem__(self, key, value, /)
| Set self[key] to value.
|
| __sizeof__(self, /)
| Return the size of the list in memory, in bytes.
|
| append(self, object, /)
| Append object to the end of the list.
|
| clear(self, /)
| Remove all items from list.
|
| copy(self, /)
| Return a shallow copy of the list.
|
| count(self, value, /)
| Return number of occurrences of value.
|
| extend(self, iterable, /)
| Extend list by appending elements from the iterable.
|
| index(self, value, start=0, stop=9223372036854775807, /)
| Return first index of value.
|
| Raises ValueError if the value is not present.
|
| insert(self, index, object, /)
| Insert object before index.
|
| pop(self, index=-1, /)
| Remove and return item at index (default last).
|
| Raises IndexError if list is empty or index is out of range.
|
| remove(self, value, /)
| Remove first occurrence of value.
|
| Raises ValueError if the value is not present.
|
| reverse(self, /)
| Reverse *IN PLACE*.
|
| sort(self, /, *, key=None, reverse=False)
| Stable sort *IN PLACE*.
|
| ----------------------------------------------------------------------
| Static methods defined here:
|
| __new__(*args, **kwargs) from builtins.type
| Create and return a new object. See help(type) for accurate signature.
|
| ----------------------------------------------------------------------
| Data and other attributes defined here:
|
| __hash__ = None
將一個(gè)可迭代對(duì)象轉(zhuǎn)為列表。不傳參數(shù)將得到空列表括尸。
type(list)
type
list()
[]
list('123')
['1', '2', '3']
list({'a':1,'b':2})
['a', 'b']
locals() 返回局部變量的字典
內(nèi)置函數(shù) locals()仲智，Python 官方文檔描述如下：
help(locals)
Help on built-in function locals in module builtins:
locals()
Return a dictionary containing the current scope's local variables.
NOTE: Whether or not updates to this dictionary will affect name lookups in
the local scope and vice-versa is *implementation dependent* and not
covered by any backwards compatibility guarantees.
返回包含當(dāng)前作用域的局部變量的字典。在模塊層級(jí)上姻氨，locals() 和 globals() 是同一個(gè)字典钓辆。
globals() 和 locals() 函數(shù)各自返回當(dāng)前的全局和本地字典，因此可以將它們傳遞給 eval() 或 exec() 來使用肴焊。
locals()
{'__name__': '__main__',
'__doc__': 'Automatically created module for IPython interactive environment',
'__package__': None,
'__loader__': None,
'__spec__': None,
'__builtin__': <module 'builtins' (built-in)>,
'__builtins__': <module 'builtins' (built-in)>,
'_ih': ['', 'help(locals)', 'locals()'],
'_oh': {},
'_dh': ['D:\\Jupyter\\xuecn_books\\books\\xue_python_kp\\11_built-in_function'],
'In': ['', 'help(locals)', 'locals()'],
'Out': {},
'get_ipython': <bound method InteractiveShell.get_ipython of <ipykernel.zmqshell.ZMQInteractiveShell object at 0x0000023E24AE89B0>>,
'exit': <IPython.core.autocall.ZMQExitAutocall at 0x23e27368898>,
'quit': <IPython.core.autocall.ZMQExitAutocall at 0x23e27368898>,
'_': '',
'__': '',
'___': '',
'_i': 'help(locals)',
'_ii': '',
'_iii': '',
'_i1': 'help(locals)',
'_i2': 'locals()'}
def f():
a = 1
print(locals())
f()
{'a': 1}
map 以給定函數(shù)轉(zhuǎn)換元素
內(nèi)置函數(shù)（類）map前联，Python 官方文檔描述如下：
help(map)
Help on class map in module builtins:
class map(object)
| map(func, *iterables) --> map object
|
| Make an iterator that computes the function using arguments from
| each of the iterables. Stops when the shortest iterable is exhausted.
|
| Methods defined here:
|
| __getattribute__(self, name, /)
| Return getattr(self, name).
|
| __iter__(self, /)
| Implement iter(self).
|
| __next__(self, /)
| Implement next(self).
|
| __reduce__(...)
| Return state information for pickling.
|
| ----------------------------------------------------------------------
| Static methods defined here:
|
| __new__(*args, **kwargs) from builtins.type
| Create and return a new object. See help(type) for accurate signature.
返回一個(gè)將函數(shù) func 應(yīng)用于 iterable 中每一項(xiàng)并輸出其結(jié)果的迭代器。
如果傳入了額外的 iterable 參數(shù)娶眷，func 必須接受相同個(gè)數(shù)的實(shí)參并被應(yīng)用于從所有可迭代對(duì)象中并行獲取的項(xiàng)似嗤。
當(dāng)有多個(gè)可迭代對(duì)象時(shí)，最短的可迭代對(duì)象耗盡則整個(gè)迭代就將結(jié)束届宠。
type(map)
type
a = map(int, '1234')
a
<map at 0x16048be3828>
list(a)
[1, 2, 3, 4]
m = map(int,'abc',(16,16))
list(m)
[10, 11]
def f(x,y):
d = {}
d[x] = y
return d
m = map(f,'abc',(1,2))
list(m)
[{'a': 1}, {'b': 2}]
max() 求最大項(xiàng)
內(nèi)置函數(shù) max()烁落，Python 官方文檔描述如下：
help(max)
Help on built-in function max in module builtins:
max(...)
max(iterable, *[, default=obj, key=func]) -> value
max(arg1, arg2, *args, *[, key=func]) -> value
With a single iterable argument, return its biggest item. The
default keyword-only argument specifies an object to return if
the provided iterable is empty.
With two or more arguments, return the largest argument.
返回可迭代對(duì)象中最大的元素，或多個(gè)實(shí)參中最大的項(xiàng)豌注。參數(shù)說明：
- 如果只提供了一個(gè)位置參數(shù)伤塌，它必須是可迭代對(duì)象（iterable），返回 iterable 中最大的元素轧铁，iterable 為空每聪，返回 default。
- 如果提供了兩個(gè)及以上的位置參數(shù)齿风，則返回最大的位置參數(shù)药薯。
- 如果有多個(gè)最大元素，則此函數(shù)將返回第一個(gè)找到的救斑。
- 參數(shù) key（可選）指定排序函數(shù)童本，將排序的項(xiàng)都經(jīng)此函數(shù)計(jì)算，按計(jì)算值取最大的項(xiàng)脸候。
max('3142')
'4'
max([], default=0)
0
max(2,4,3,4)
4
max([2,1],[2,1,1])
[2, 1, 1]
max(('a','ab','bcd'),key=len)
'bcd'
min() 求最小項(xiàng)
內(nèi)置函數(shù) min()穷娱，Python 官方文檔描述如下：
help(min)
Help on built-in function min in module builtins:
min(...)
min(iterable, *[, default=obj, key=func]) -> value
min(arg1, arg2, *args, *[, key=func]) -> value
With a single iterable argument, return its smallest item. The
default keyword-only argument specifies an object to return if
the provided iterable is empty.
With two or more arguments, return the smallest argument.
返回可迭代對(duì)象中最小的元素，或多個(gè)實(shí)參中最小的項(xiàng)纪他。參數(shù)說明：
- 如果只提供了一個(gè)位置參數(shù)鄙煤，它必須是可迭代對(duì)象（iterable），返回 iterable 中最小的元素茶袒，iterable 為空梯刚，返回 default。
- 如果提供了兩個(gè)及以上的位置參數(shù)薪寓，則返回最小的位置參數(shù)亡资。
- 如果有多個(gè)最小元素澜共，則此函數(shù)將返回第一個(gè)找到的。
- 參數(shù) key（可選）指定排序函數(shù)锥腻，將排序的項(xiàng)都經(jīng)此函數(shù)計(jì)算嗦董，按計(jì)算值取最小的項(xiàng)。
min('3142')
'1'
min([], default=0)
0
min(2,3,2,4)
2
min([2,1],[2,1,1])
[2, 1]
min(('a','ab','bcd'),key=len)
'a'
next() 返回迭代器下一個(gè)元素
內(nèi)置函數(shù) next()瘦黑，Python 官方文檔描述如下：
help(next)
Help on built-in function next in module builtins:
next(...)
next(iterator[, default])
Return the next item from the iterator. If default is given and the iterator
is exhausted, it is returned instead of raising StopIteration.
返回迭代器（iterator）的下一個(gè)元素京革。如果迭代器耗盡，則返回給定的 default幸斥，如果沒有默認(rèn)值則觸發(fā) StopIteration匹摇。
i = iter('123')
next(i,'迭代結(jié)束')
'1'
next(i,'迭代結(jié)束')
'2'
next(i,'迭代結(jié)束')
'3'
next(i,'迭代結(jié)束')
'迭代結(jié)束'
next(i,'迭代結(jié)束')
'迭代結(jié)束'
