4.8Python内置函数

4.8Python内置函数

example4.8.1

>>> #返回数字绝对值 abs（）
>>> abs(-520)
520
>>> abs

example4.8.2

>>>#返回最大值和最小值 max（）、min()
>>> a = [1,2,3,4,5,520,815]
>>> max(a)
815
>>> min(a)
1
>>>

example4.8.3

>>> #求字符串长度len()
>>> a = [1,2,3,4,5,520,815]
>>> s = 'cuixiaohui'
>>> len(s)
10
>>> len(a)
7

example4.8.4

>>> help(divmod)
Help on built-in function divmod in module builtins:

divmod(...)
divmod(x, y) -> (div, mod)

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

>>>#求商和模divmod()
>>> divmod(2,5)
(0, 2)
>>> divmod(5,2)
(2, 1)
>>> divmod(100,100)
(1, 0)

example4.8.5

>>> help(pow)
Help on built-in function pow in module builtins:

pow(...)
pow(x, y[, z]) -> number

With two arguments, equivalent to x**y.  With three arguments,
equivalent to (x**y) % z, but may be more efficient (e.g. for ints).

>>> #求次方
>>> pow(3,3)
27
>>> #求次方的模
>>> pow(3,3,7)
6

example4.8.6

>>> help(round)
Help on built-in function round in module builtins:

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

Round a number to a given precision in decimal digits (default 0 digits).
This returns an int when called with one argument, otherwise the
same type as the number. ndigits may be negative.

>>> round(520)
520

example4.8.7

>>> help(callable)
Help on built-in function callable in module builtins:

callable(...)
callable(object) -> bool

Return whether the object is callable (i.e., some kind of function).
Note that classes are callable, as are instances of classes with a
__call__() method.

>>> #判断一个对象是否可以用（函数是否定义）
>>> callable(f)
Traceback (most recent call last):
File "<pyshell#52>", line 1, in <module>
callable(f)
NameError: name 'f' is not defined

>>> def f(x):
if x< 0:
return  -x
return x

>>> callable(f)
True

example4.8.8

>>> help(isinstance)
Help on built-in function isinstance in module builtins:

isinstance(...)
isinstance(object, class-or-type-or-tuple) -> bool

Return whether an object is an instance of a class or of a subclass thereof.
With a type as second argument, return whether that is the object's type.
The form using a tuple, isinstance(x, (A, B, ...)), is a shortcut for
isinstance(x, A) or isinstance(x, B) or ... (etc.).

>>> #判断某一对象的类型
>>> a=[1, 2, 3, 4, 5, 520, 815]
>>> type(a)
<class 'list'>
>>> isinstance(a,list)
True
>>> isinstance(a,int)
False
>>>

example4.8.9

#cmp()在python3.3.3未定义
>>> help(cmp)
Traceback (most recent call last):
File "<pyshell#64>", line 1, in <module>
help(cmp)
NameError: name 'cmp' is not defined
>>> cmp('lixiaotao','lixiao')
Traceback (most recent call last):
File "<pyshell#65>", line 1, in <module>
cmp('lixiaotao','lixiao')
NameError: name 'cmp' is not defined
>>>
#cmp()是比较两个字符串是否一样
#假设已经定义，举例如下
>>> cmp('hello','hello')
0
>>> cmp('h','hello')
-1
>>> cmp('hhhhhhh','hello')
1

example4.8.10

#快速生成一个序列range（）
#xrange（）在python3.3.3未定义

>>> range(10)
range(0, 10)
>>> help(range)
Help on class range in module builtins:

class range(object)
|  range(stop) -> range object
|  range(start, stop[, step]) -> range object
|
|  Return a virtual sequence of numbers from start to stop by step.
|
|  Methods defined here:
|
|  __contains__(...)
|      x.__contains__(y) <==> y in x
|
|  __eq__(...)
|      x.__eq__(y) <==> x==y
|
|  __ge__(...)
|      x.__ge__(y) <==> x>=y
|
|  __getattribute__(...)
|      x.__getattribute__('name') <==> x.name
|
|  __getitem__(...)
|      x.__getitem__(y) <==> x[y]
|
|  __gt__(...)
|      x.__gt__(y) <==> x>y
|
|  __hash__(...)
|      x.__hash__() <==> hash(x)
|
|  __iter__(...)
|      x.__iter__() <==> iter(x)
|
|  __le__(...)
|      x.__le__(y) <==> x<=y
|
|  __len__(...)
|      x.__len__() <==> len(x)
|
|  __lt__(...)
|      x.__lt__(y) <==> x<y
|
|  __ne__(...)
|      x.__ne__(y) <==> x!=y
|
|  __reduce__(...)
|
|  __repr__(...)
|      x.__repr__() <==> repr(x)
|
|  __reversed__(...)
|      Return a reverse iterator.
|
|  count(...)
|      rangeobject.count(value) -> integer -- return number of occurrences of value
|
|  index(...)
|      rangeobject.index(value, [start, [stop]]) -> integer -- return index of value.
|      Raise ValueError if the value is not present.
|
|  ----------------------------------------------------------------------
|  Data descriptors defined here:
|
|  start
|
|  step
|
|  stop
|
|  ----------------------------------------------------------------------
|  Data and other attributes defined here:
|
|  __new__ = <built-in method __new__ of type object>
|      T.__new__(S, ...) -> a new object with type S, a subtype of T

>>> help(xrange)
Traceback (most recent call last):
File "<pyshell#68>", line 1, in <module>
help(xrange)
NameError: name 'xrange' is not defined

example4.8.11

类型转化函数

type（）

int（）

long()

float()

complex() 复数

>>>#举例
>>> s='520'
>>> type(s)
<class 'str'>
>>> s + 520
Traceback (most recent call last):
File "<pyshell#75>", line 1, in <module>
s + 520
TypeError: Can't convert 'int' object to str implicitly
>>> int(s)
520
>>> int(s) + 520
1040
>>>

example4.8.12

类型转化函数

str()

list()

tuple()

hex()

oct()

chr()

ord()

>>> help(hex)
Help on built-in function hex in module builtins:

hex(...)
hex(number) -> string

Return the hexadecimal representation of an integer.

>>> help(oct)
Help on built-in function oct in module builtins:

oct(...)
oct(number) -> string

Return the octal representation of an integer.

>>> help(chr)
Help on built-in function chr in module builtins:

chr(...)
chr(i) -> Unicode character

Return a Unicode string of one character with ordinal i; 0 <= i <= 0x10ffff.

>>> help(ord)
Help on built-in function ord in module builtins:

ord(...)
ord(c) -> integer

Return the integer ordinal of a one-character string.

>>>

注：学习内容来源于网易云课堂《疯狂的Python：快速入门精讲》；代码执行环境为Win；Python版本为 3.3.3