02-python Base II (basic data type)

one, intro.

1 What is data?

x=10,10 is the data we want to store.

2 Why data is divided into different types

Data is used to represent States, and different States should be represented by different types of data.

3 Data types

Digital

String

List

Meta-group

Dictionary

Collection

two basic data types. 2.1 Numeric int.

The number is mainly used for computing, not many ways to use, just remember one can:

#bit_length () The minimum number of bits to use when the decimal is in binary notation v = 11data = V.bit_length () print (data)

2.2 boolean bool.

There are two types of Boolean values: True,false. is the correct condition of the reaction.

True 1 true.

False 0 false.

2.3 String str.

2.3.1, the index of the string, and the slice.

The index is subscript, that is, the elements of the string begin with the first, the initial index is 0, and so on.

A = ' Abcdefghijk ' Print (a[0]) print (a[3]) print (a[5]) print (a[7])

A slice is a section of a string that is intercepted by an index (index: Index: STRIDE), forming a new string (the principle is that Gu head ignores butt).

A = ' Abcdefghijk ' Print (A[0:3]) print (A[2:5]) print (a[0:]) #默认到最后print (a[0:-1]) #-1 is the last print (A[0:5:2]) #加步长
Print (A[5:0:-2]) #反向加步长

2.3.2, String common methods.

View Code 2.4 Yuan zu tupe.

Tuples are called read-only lists, where data can be queried but cannot be modified, so the slicing of strings also applies to tuples. Example: ("A", "B", "C")

List of 2.5 lists.

The list is one of the underlying data types in Python, and other languages have data types similar to lists, such as JS called arrays, which are enclosed in [] and each element is separated by commas, and he can store various data types such as:

Li = [' Alex ', 123,ture, (Wusir), [All-in-all, ' xiaoming ',],{' name ': ' Alex '}]

Compared to strings, lists can store not only different data types, but also large amounts of data, 32-bit Python is limited to 536,870,912 elements, and 64-bit Python is limited to 1.,152,921,504,606,85e,+18 elements. And the list is ordered, there are index values, can be sliced, convenient to take value.

2.5.1, increase .

The list increases

2.5.2, delete .

the deletion of the list

2.5.3, change .

changes to the list

2.5.4, check .

Slice it, or cycle it.

2.5.5, other operations .

Count (number) (the method counts the number of occurrences of an element in the list).

1 a = ["Q", "W", "Q", "R", "T", "Y"]2 print (A.count ("Q"))

Index (method used to find the index position of the first occurrence of a value from the list)

1 a = ["Q", "W", "R", "T", "Y"]2 print (A.index ("R"))

Sort (the method is used to sort the list at the original location).

Reverse (the method stores the elements in the list in reverse).

1 A = [2,1,3,4,5]2 a.sort () # He has no return value, so it can only print A3 print (a) 4 a.reverse () #他也没有返回值, so only A5 print (a) can be printed

2.6 Dictionary Dict.

　　A dictionary is the only type of mapping in Python that stores data in the form of key-value pairs (key-value). Python computes the hash function of key and determines the storage address of value based on the computed result, so the dictionary is stored out of order and the key must be hashed. A hash indicates that a key must be an immutable type, such as a number, a string, a tuple.

The Dictionary (dictionary) is the most flexible built-in data structure type in addition to the list of unexpected python. A list is an ordered combination of objects, and a dictionary is a collection of unordered objects. The difference between the two is that the elements in the dictionary are accessed by keys, not by offsets.

2.6.1, increase .

The increase in the dictionary

2.6.2, delete .

the deletion of the dictionary

2.6.3, change .

The change of the dictionary

2.6.4, check .

the dictionary search

2.6.5, other operations.

View Code

The cycle of the dictionary.

# dic = {"Name": "Jin", "Age": +, "sex": "Male"}# for key in dic:#     print (key) # for item in Dic.items (): #     Print (item ) # for Key,value in Dic.items (): #     print (Key,value)

third, other (For,enumerate,range).

For loop: The user iterates through the contents of an object in order.

msg = ' old boy python is the best Python training institution in the country ' for item in msg:    print (item) li = [' Alex ', ' Silver Horn ', ' goddess ', ' Egon ', ' Taibai ']for i in Li:    Print (i) dic = {' name ': ' Taibai ', ' age ': +, ' sex ': ' Man '}for k,v in Dic.items ():    print (K,V)

Enumerate: enumerations, for an iterative (iterable)/traversed object (such as a list, string), enumerate it into an index sequence that can be used to obtain both the index and the value.

Li = [' Alex ', ' Silver Horn ', ' goddess ', ' Egon ', ' Taibai ']for i in Enumerate (LI):    print (i) for index,name in Enumerate (li,1):    print ( Index,name) for index, name in enumerate (Li, s):  # start position default is 0, can change    print (index, name)

Range: Specifies a range that generates the specified number.

For I in Range (1,10):    print (i) for I in Range (1,10,2):  # step    print (i) for I in Range (10,1,-2): # Reverse Step    prin T (i)

02-python Base II (basic data type)