Python learning 04-Data types (tuples, dictionaries, collections)

First, the basic data type--tuple

Tuple: is a data type that is very similar to a list. However, once created it can no longer be modified, so it is called a read-only list.

Definition: Similar to a list, except [] Change to ()

　　Characteristics:

1. Can hold multiple values (can hold complex data types)
2. Immutable ( explicitly telling someone that data is not modifiable, often used for database connection configuration information, etc. )
3. The tuple elements are defined in order from left to right, and the subscript is accessed sequentially from 0, ordered
4. The tuple itself is immutable, and these mutable elements can be changed if the tuple also contains other mutable elements. (such as lists, etc.)

Tuples Common operations

Create

Ages = (one, 22, 33, 44, 55)# or ages = tuple ((11)

Index & Slice

#Index>>> ages = (11, 22, 33, 44, 55)>>>Ages[0]11>>> ages[3]44>>> ages[-1]55#slices>>> name = ('Egon','Alex','Seven','Yuan')>>> Name[0:2]('Egon','Alex')>>> Name[2:5]('Seven','Yuan')>>> Name[:2]('Egon','Alex')>>> name[2:] ('Seven','Yuan')>>>name[:] ('Egon','Alex','Seven','Yuan')

Inclusions, lengths, and loops

>>> ages = (one, one, one, one, one) in ages                 #  contains True in Agesfalse  not inch agesfalse>>> Len (ages)                  #  length  for in ages:         # Loop ...     Print (age) ... 1122334455

II. basic Data Type--dictionary

A dictionary is the only type of mapping in the Python language.
Definition: {key1:value1,key2:value2}

1. The keys and values are separated by a colon ":";
2. The item is separated from the item with a comma ",";

Characteristics:

1. Key-value structure
2. Key must be hash, must be immutable data type, must be unique
3. can store any number of values, can be modified, can not be unique
4. Disordered

Dictionary common Operations

Dictionary creation

person = {"name":"Alex",' Age': 20}#orperson = dict (name='Seven', age=20)#orPerson = Dict ({"name":"Egon",' Age': 20})#or Person= Dict ((['name','Yuanhao'],['Wen Zhou', 18]) {}.fromkeys (seq,100)#do not specify 100 defaults to none#Note>>> Dic={}.fromkeys (['K1','K2'],[])>>>dic{'K1': [],'K2': []}>>> dic['K1'].append (1)>>>dic{'K1': [1],'K2': [1]}

Dictionary View

#key, value, key-value pairsDic.keys ()#returns a list containing all keys for the dictionary;Dic.values ()#returns a list containing all the value of the dictionary;Dic.items ()#returns a list containing all (key, value) Ganso;#Dic.iteritems (), Dic.iterkeys (), and dic.itervalues () are the same as the non-iterative methods they correspond to, but they return an iteration instead of a list;#Viewdic['Key']#returns the value corresponding to the key in the dictionary, or an error if the key does not exist in the dictionary;Dict.get (key, default = None)#returns the value of the key in the dictionary, or the value of default if the key does not exist in the dictionary (default defaults to None)#Loops forKinchDic.keys () forKvinchDic.items () forKinchDiC#lengthLen (DIC)

Dictionary additions and Deletions change

#Newdic['New_key'] ='New_value'Dic.setdefault (Key, None)#If the key key does not exist in the dictionary, it is assigned by dic[key] = default; _#DeleteDic.pop (Key[,default])#similar to the Get method. If there is a key in the dictionary, delete and return the key corresponding to the Vuale; if the key does not exist and the default value is not given, the keyerror exception is thrown;Dic.clear ()#Delete all items or elements in the dictionary;#Modifydic['Key'] ='New_value'           #if key exists in the dictionary, ' New_value ' will replace the original valueDic.update (DIC2)#Add dictionary dic2 key-value pairs to dictionary dic

III. basic data Types--collections

A collection is a mathematical concept: a whole is called a set, consisting of one or more determined elements.
The elements in the collection have three characteristics:

1. Deterministic (element must be hash)
2. Cross-specific (go-to-weight)--Change a list to a set and automatically go heavy
3. Unordered (the elements in the collection have no successive points), such as the collection {3,4,5} and {3,5,4} count as the same collection.

　Note: The meaning of a set exists in the de-emphasis and relational operations

Relational operations: The intersection of two sets of data, the difference set, and the relationship between the set.

collection creation and relational operations

s = {1,2,3,2,4,5}#Create a collections = set ([1,3,4,5,6])#Convert to CollectionIphone7= {'Alex','Rain','Jack','Old_driver'}iphone8= {'Alex','Shanshan','Jack','Old_boy'}#intersectioniphone7.intersection (Iphone8)#intersectionIphone7 &Iphone8#Difference SetIphone7.difference (Iphone8)#Iphone7, there's Iphone8.#Difference SetIphone7-Iphone8#and set (de-weight)iphone7.union (Iphone8)#and setIphone8 | Iphone7#Pipe character#symmetric difference set (only for people who bought IPhone7 or Iphone8)iphone8.symmetric_difference (Iphone7)#Symmetric difference SetsIphone7 ^ Iphone8

Include relationship

• In,not in: Determines whether an element is within the set
• ==,! =: Determine whether two sets are equal

There are generally three relationships between two collections, Intersect, include, and do not intersect. In Python, the following methods are used to determine:

1. Set.isdisjoint (s): Determine if two sets are disjoint
2. Set.issuperset (s): Determines whether the collection contains other collections, equivalent to A>=b
3. Set.issubset (s): Determines whether a collection is contained by another collection, equivalent to A<=b

Collection of the increase, deletion, search

" "The addition of a single element: Add (), the effect of add is similar to the list of append to increase the sequence: update (), and update similar to the Extend method, the Update method can support the simultaneous passing of multiple parameters:" ">>> a={1,2}>>> A.update ([3,4],[1,2,7])>>>a{1, 2, 3, 4, 7}>>> A.update ("Hello")>>>a{1, 2, 3, 4, 7,'h','e','L','o'}>>> A.add ("Hello")>>>a{1, 2, 3, 4,'Hello', 7,'h','e','L','o'}" "Deleting A collection of elements there are two ways to delete a single element: When the element is not in the original collection: Set.discard (x) does not throw an exception Set.remove (x) throws Keyerror error >>> a={1,2,3,4}" ">>> a={1,2,3,4}>>> A.discard (1)>>>a{2, 3, 4}>>> A.discard (1)>>>a{2, 3, 4}>>> A.remove (1) Traceback (most recent): File"<input>", Line 1,inch<module>Keyerror:1" "pop (): Because the collection is unordered, the result of the pop return cannot be determined, and calling pop when the collection is empty throws a Keyerror error, clear (): Empties the collection" ">>> A={3,"a", 2.1,1}>>>A.pop ()>>>A.pop ()>>>a.clear ()>>>aset ()>>>A.pop () Traceback (most recent): File"<input>", Line 1,inch<module>Keyerror:'pop from an empty set'

Python learning 04-Data types (tuples, dictionaries, collections)