"Python" 06, Python built-in data structure 1

I. Data structure and access to help information

1. Data structure

A collection of data elements that are organized in a way, such as numbering elements , that can be numbers or characters, or even other data structures.

The most basic data structure of Python is the sequence

each element in the sequence is assigned an ordinal (that is, the position of the element), also known as an index : The index is numbered starting at 0

2. How to get command Help in Python

Gets the properties and methods used by the object:dir (),

Specific use of a method helps: Help()

Gets the document string for the callable object:print (obj.__doc__)

In [15]: dir (list) out[15]: [' __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 ']  in [17]: help (list) help  on list object: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.  in [20]: print (list.__doc__) list ()  -> new  empty listlist (iterable)  -> new list initialized from iterable ' s itemsin [21]: list.__doc__ out[21]:  "list ()  -> new empty list\nlist (iterable)  -> new list  initialized from iterable ' S items '

Second, List

1. List

list : is an ordered collection of positions related to an arbitrary type of object.

A list is a sequence that is used to store data sequentially

The definition and initialization of a list:

In [5]: Lst1 = list () # using the Factory function list () in [6]: Lst2 = [] # using []in [7]: Type (LST1) out[7]: Listin [8]: type (LST2) OUT[8]: Listin [9]: Lst1 = List (range (10)) # Convert an iterative object to a list in [ten]: lst1out[10]: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

usually use the brackets when defining the list, and use the list () when converting an iteration object

Third, list-related operations

On the list generally have to increase, delete, change, check the relevant operation

1. Check

1) Access to the elements of the list by index (subscript)

returns the element corresponding to the index

index starting from the left, starting from 0, cannot go out of range, otherwise throws Indexerror

Negative index starts from the right, starting from 1

In []: lst1out[25]: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]in []: lst1[0]out[26]: 0In [+]: lst1[10]--------------------------- ------------------------------------------------Indexerror Traceback (most recent ) <ipython-input-27-255d55760a91> in <module> ()----> 1 lst1[10]indexerror:list index out of Rangein [28]: LST1[-1]OUT[28]: 9In []: lst1[-3]out[29]: 7In [in]: lst1[-3]

2) List.index ()

returns the first index found to the element

If the element does not exist, the ValueError is thrown

The start parameter specifies the index from which to start the lookup; the stop parameter specifies which index to end from and does not contain the index

Start and stop can be negative, but always look from left to right

In [51]: help (Lst2.index) help on built-in function index:index (...)  method of builtins.list instance    l.index (value, [start,  [Stop]]  -> integer -- return first index of value.     Raises valueerror if the value is not present.    in  [47]: lst2=[1, 3, 5, 2, 3, 5]in [48]: lst2.index (3) Out[48]:  1in [49]: lst2.index (2) Out[49]: 3in [52]: lst2.index (8)------------------------ ---------------------------------------------------valueerror                                  Traceback  (Most recent call last) < Ipython-input-52-857c8a1f260a> in&nBsp;<module> ()----> 1 lst2.index (8) Valueerror: 8 is not in listin  [56]: lst2.index (3, 3) out[56]: 4in [57]: lst2.index (3, 3, 4)--------- ------------------------------------------------------------------valueerror                                  Traceback  (Most recent call last) <ipython-input-57-dd5e9d56cf7c> in <module> ()----> 1 lst2.index (3, 3,  4) Valueerror: 3 is not in listin [59]: lst2.index (3, 3, 5) Out[59]: 4in [60]: lst2.index (3, 4, 5) Out[60]: 4in [70]: lst2.index (3,  -1, -6,)    # start  greater than  stop  is an empty list     ------- --------------------------------------------------------------------valueerror                                  Traceback  (Most recent call last) < Ipython-input-70-b3ae59853639> in <module> ()----> 1 lst2.index (3, -1,  -6,) Valueerror: 3 is not in listin [71]: lst2.index (3, -6,  -1,) Out[71]: 1in [74]: lst2.index (3, -6, 9,) In [98]: lst2.index (3, 1,  1)---------------------------------------------------------------------------valueerror                                  Traceback  (most recent  Call last) <ipython-input-98-a95f8fe9908B> in <module> ()----> 1 lst2.index (3, 1, 1) ValueError: 3  Is not in listin [99]: lst2.index (3, 1, 2) Out[99]: 1

The implementation of the List.index () function is prototyped:

def index (LST, value, start = 0, stop =-1): i = start for x in lst[start:end] if x = = Value:ret Urn I i + = 1 Rais valueerror ()

3) List.count ()

returns the number of occurrences of this value in the list

In [lst2out[89]: [1, 3, 5, 2, 3, 5]in [all]: Lst2.count (1) out[90]: 1In []: Lst2.count (5) out[91]: 2In []: Lst2.coun T (8) out[92]: 0

Prototype:

def count (lst, value): c = 0 for x in lst:if x = = Value:c + 1 return c

Summary:

The time complexity of index () and count () is O (n), also called linear complexity; efficiency is linearly correlated with data size

"Python" 06, Python built-in data structure 1