记录一些python内置函数

整理一些内置函数，平时用得比较少，但是时不时遇上，记录一下吧（嘻嘻(●'◡'●)）

1.help()

查看模块or函数的帮助文档

help(pandas)  #模块

Help on package pandas:
NAME
    pandas
DESCRIPTION
    pandas - a powerful data analysis and manipulation library for Python
    =====================================================================
    **pandas** is a Python package providing fast, flexible, and expressive data
    structures designed to make working with "relational" or "labeled" data both
    easy and intuitive. It aims to be the fundamental high-level building block for
    doing practical, **real world** data analysis in Python. Additionally, it has
    the broader goal of becoming **the most powerful and flexible open source data
    analysis / manipulation tool available in any language**. It is already well on
    its way toward this goal.
    Main Features
    -------------
    Here are just a few of the things that pandas does well:
      - Easy handling of missing data in floating point as well as non-floating
        point data
      - Size mutability: columns can be inserted and deleted from DataFrame and
        higher dimensional objects
      - Automatic and explicit data alignment: objects can  be explicitly aligned
        to a set of labels, or the user can simply ignore the labels and let
        `Series`, `DataFrame`, etc. automatically align the data for you in
        computations
      - Powerful, flexible group by functionality to perform split-apply-combine
        operations on data sets, for both aggregating and transforming data
      - Make it easy to convert ragged, differently-indexed data in other Python
        and NumPy data structures into DataFrame objects
      - Intelligent label-based slicing, fancy indexing, and subsetting of large
        data sets
      - Intuitive merging and joining data sets
      - Flexible reshaping and pivoting of data sets
      - Hierarchical labeling of axes (possible to have multiple labels per tick)
      - Robust IO tools for loading data from flat files (CSV and delimited),
        Excel files, databases, and saving/loading data from the ultrafast HDF5
        format
      - Time series-specific functionality: date range generation and frequency
        conversion, moving window statistics, moving window linear regressions,
        date shifting and lagging, etc.
PACKAGE CONTENTS
    _libs (package)
    _version
    api (package)
    compat (package)
    computation (package)
    conftest
    core (package)
    errors (package)
    formats (package)
    io (package)
    json
    lib
    parser
    plotting (package)
    stats (package)
    testing
    tests (package)
    tools (package)
    tseries (package)
    tslib
    types (package)
    util (package)
SUBMODULES
    _hashtable
    _lib
    _tslib
    offsets
DATA
    IndexSlice = <pandas.core.indexing._IndexSlice object>
    NaT = NaT
    __docformat__ = 'restructuredtext'
    datetools = <module 'pandas.core.datetools' from 'F:\\Anaconda\\lib\\s...
    describe_option = <pandas.core.config.CallableDynamicDoc object>
    get_option = <pandas.core.config.CallableDynamicDoc object>
    options = <pandas.core.config.DictWrapper object>
    plot_params = {'xaxis.compat': False}
    reset_option = <pandas.core.config.CallableDynamicDoc object>
    set_option = <pandas.core.config.CallableDynamicDoc object>
VERSION
    0.20.3
FILE
    f:\anaconda\lib\site-packages\pandas\__init__.py

help(list)  #函数

Help on class list in module builtins:
class list(object)
 |  list() -> new empty list
 |  list(iterable) -> new list initialized from iterable's items
 |
 |  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.n
 |
 |  __ne__(self, value, /)
 |      Return self!=value.
 |
 |  __new__(*args, **kwargs) from builtins.type
 |      Create and return a new object.  See help(type) for accurate signature.
 |
 |  __repr__(self, /)
 |      Return repr(self).
 |
 |  __reversed__(...)
 |      L.__reversed__() -- return a reverse iterator over the list
 |
 |  __rmul__(self, value, /)
 |      Return self*value.
 |
 |  __setitem__(self, key, value, /)
 |      Set self[key] to value.
 |
 |  __sizeof__(...)
 |      L.__sizeof__() -- size of L in memory, in bytes
 |
 |  append(...)
 |      L.append(object) -> None -- append object to end
 |
 |  clear(...)
 |      L.clear() -> None -- remove all items from L
 |
 |  copy(...)
 |      L.copy() -> list -- a shallow copy of L
 |
 |  count(...)
 |      L.count(value) -> integer -- return number of occurrences of value
 |
 |  extend(...)
 |      L.extend(iterable) -> None -- extend list by appending elements from the iterable
 |
 |  index(...)
 |      L.index(value, [start, [stop]]) -> integer -- return first index of value.
 |      Raises ValueError if the value is not present.
 |
 |  insert(...)
 |      L.insert(index, object) -- insert object before index
 |
 |  pop(...)
 |      L.pop([index]) -> item -- remove and return item at index (default last).
 |      Raises IndexError if list is empty or index is out of range.
 |
 |  remove(...)
 |      L.remove(value) -> None -- remove first occurrence of value.
 |      Raises ValueError if the value is not present.
 |
 |  reverse(...)
 |      L.reverse() -- reverse *IN PLACE*
 |
 |  sort(...)
 |      L.sort(key=None, reverse=False) -> None -- stable sort *IN PLACE*
 |
 |  ----------------------------------------------------------------------
 |  Data and other attributes defined here:
 |
 |  __hash__ = None

2.hex()

将十进制转成十六进制(括号里放十进制的数),返回一个字符串

hex(10)

'0xa'

hex(99)

'0x63'

type(hex(99))

str

3.oct()

将十进制转成八进制，返回一个字符串

oct(1307)

'0o2433'

oct(2013)

'0o3735'

type(oct(2013))

str

4.bin()

将十进制转成二进制，返回一个字符串

bin(6)

'0b110'

type(bin(6))

str

5.id()

获取对象的内存地址

a = "小可爱"
id(a)

496383449200

b = 20160101
id(b)

496382826736

6.dir()

dir() 函数不带参数时，返回当前范围内的变量、方法和定义的类型列表；

带参数时，返回参数的属性、方法列表。

如果参数包含方法__dir__()，该方法将被调用。

如果参数不包含__dir__()，该方法将最大限度地收集参数信息

dir()

['In',
 'Out',
 '_',
 '_1',
 '_10',
 '_11',
 '_12',
 '_14',
 '_15',
 '_16',
 '_17',
 '_18',
 '_19',
 '_2',
 '_20',
 '_22',
 '_23',
 '_24',
 '_25',
 '_26',
 '_27',
 '_28',
 '_29',
 '_3',
 '_30',
 '_31',
 '_33',
 '_35',
 '_38',
 '_39',
 '_4',
 '_40',
 '_41',
 '_42',
 '_43',
 '_44',
 '_45',
 '_5',
 '_6',
 '__',
 '___',
 '__builtin__',
 '__builtins__',
 '__doc__',
 '__loader__',
 '__name__',
 '__package__',
 '__spec__',
 '_dh',
 '_i',
 '_i1',
 '_i10',
 '_i11',
 '_i12',
 '_i13',
 '_i14',
 '_i15',
 '_i16',
 '_i17',
 '_i18',
 '_i19',
 '_i2',
 '_i20',
 '_i21',
 '_i22',
 '_i23',
 '_i24',
 '_i25',
 '_i26',
 '_i27',
 '_i28',
 '_i29',
 '_i3',
 '_i30',
 '_i31',
 '_i32',
 '_i33',
 '_i34',
 '_i35',
 '_i36',
 '_i37',
 '_i38',
 '_i39',
 '_i4',
 '_i40',
 '_i41',
 '_i42',
 '_i43',
 '_i44',
 '_i45',
 '_i46',
 '_i5',
 '_i6',
 '_i7',
 '_i8',
 '_i9',
 '_ih',
 '_ii',
 '_iii',
 '_oh',
 'a',
 'b',
 'exit',
 'get_ipython',
 'numpy',
 'pandas',
 'quit',
 'result',
 'sys',
 'x']

dir(list)

['__add__',
 '__class__',
 '__contains__',
 '__delattr__',
 '__delitem__',
 '__dir__',
 '__doc__',
 '__eq__',
 '__format__',
 '__ge__',
 '__getattribute__',
 '__getitem__',
 '__gt__',
 '__hash__',
 '__iadd__',
 '__imul__',
 '__init__',
 '__init_subclass__',
 '__iter__',
 '__le__',
 '__len__',
 '__lt__',
 '__mul__',
 '__ne__',
 '__new__',
 '__reduce__',
 '__reduce_ex__',
 '__repr__',
 '__reversed__',
 '__rmul__',
 '__setattr__',
 '__setitem__',
 '__sizeof__',
 '__str__',
 '__subclasshook__',
 'append',
 'clear',
 'copy',
 'count',
 'extend',
 'index',
 'insert',
 'pop',
 'remove',
 'reverse',
 'sort']

7.all()

判断列表或元组中的所有元素是否都为True，如果都为True，那么就返回True。

0，空值（即""），None，False均被判定为False，其余为True。

Remember that,空列表、空元组返回的是True，不是False哦

all([1, 2, 3, 4])

True

all([0, 1, 2, 3])

False

all(["", 1, 2, 3])

False

all([None, 1])

False

all([])

True

all(())

True

8.any()

判断列表或元组中的元素，如果有一个为True，那么就返回True。

any([0, None, 1])

True

any(["", False])

False

all跟any的区别就是：all要全部True才返回True，any只要有一个True就返回True。

9.abs()

返回数字的绝对值

abs(-100)

100

abs(20170516)

20170516

10.map(function, iterable, …)

根据函数对序列做映射（看例子好懂一点）

def result(x):
    return x + 100

map(result, [1,2,3,4,5])

<map at 0x7392c4a390>

11.range(start, stop, step)

返回一个对象，instead of 一个列表（python2 返回的才是列表），用list(range())可实现输出为列表。

range(10)

range(0, 10)

list(range(10))

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

type(range(10))

range

12.chr()

返回整数（十进制or十六进制）对应的ASCII字符。

chr(2017)

'ߡ'

chr(0x666)

'٦'

13.max()

返回给定参数的最大值，参数可以为序列

max([1,2,3,4,2017])

2017

max(1,2,2333)

2333

14.min()

返回给定参数的最大值，参数可以为序列

min("a", "b", "c")

'a'

min(1307, 1401, 1206)

1206

15.len()

返回对象（字符、列表、元组等）长度或项目个数

len(("a", "b", "c"))

3

len("I love you Math!")

16

16.reversed()

返回一个反转的迭代器, 要转换的序列可以是 tuple, string, list 或 range

a = ("Mike", "love", "Cathy")
print(list(reversed(a)))

['Cathy', 'love', 'Mike']

b = [520, 1314, 5201314]
print(list(reversed(b)))

[5201314, 1314, 520]

17.sorted()

对可迭代对象进行排序操作，默认是升序（参数reverse= False）

sorted([1, 2, 999])

[1, 2, 999]

sorted([1, 2, 999], reverse=True)

[999, 2, 1]

18.isinstance()

判断一个对象是否是一个已知的类型，类似 type()

isinstance([1], list)

True

isinstance([1], dict)

False

19.type()

返回对象的类型

type(20160101)

int

type(20160101) == int

True

isinstance() 与 type() 区别：

type() 不会认为子类是一种父类类型，不考虑继承关系。

isinstance() 会认为子类是一种父类类型，考虑继承关系。

如果要判断两个类型是否相同推荐使用 isinstance()。

20.divmod()

求商、求余

divmod(8, 2)

(4, 0)

divmod(8.0, 2)

(4.0, 0.0)

divmod(-8, 2.0)

(-4.0, 0.0)

21.hash()

获取取一个对象（字符串或者数值等）的哈希值

hash('Love you')

5600379523179052084

hash(8888)

8888

hash('8888')

-5690624612815825000