Python Foundation day-3

The composition of the variable:

Variables are made up of variable names, assignment symbols, variable values, and variable types.

Variable name →n = 1← Variable Value

↑

Assignment symbols

Comparison method:

Identity comparison: The ID of the variable value is compared

>>> x = 300>>> ID (x)46137936>>> y = 300>>> id (y) is Yfalse>>>

Comparison of values: compare two variable values

>>> x = 300>>> y = 300>>> ID (x)54002288>>> ID (y)54002352>> > x = = Ytrue>>>

Type comparison: Compare types of two variables

>>> x = 300>>> y = 300>>> type (x)<class'int' >>>> type (y)<class'int' is type (y) True>>>

Variable assignment operation (supplemental):

x = 1 #就是一个赋值操作 No return value chain assignment: a=b=c=10 multivariate assignment: XY value interchange x = 1 y = 2 salted fish Exchange method: z = x x = y y = z Large God Exchange: Python: x,y=y,x Example:

>>> x = 1>>> y = 2>>> x, y =  y,x>>> 2>>> y1>&G T;>

Increment Assignment:

x = x +=1 #+-*/extract sequence type: s = ' hello ' salted fish method: a = S[0] b = s[1] ... Great God Law: a,b,c,d,e=s only print out the corresponding values of a and E, use ' _ ' to populate the middle variable, ' _ ' convention is commonly known as the discarded variable a,_,_,_,e = s A,*_,e #使用 *_ represents the middle of all

>>> s ='Hello'>>> a,b,c,d,e =s>>>a'h'>>>b'e'>>>C'L'>>>D'L'>>>e'o'>>> a,*_,b =s>>>a'h'>>>b'o'>>>

Classification:

One: variable non-changeable
mutable: List, dictionary
Immutable: Numbers, strings, tuples

Two: The number of stored values
A value: A number, a string
Multiple values (container type): list, tuple, dictionary

Three: The method of taking value
Direct value: Number
Sequence type: string, tuple, list
Mapping Type: Dictionary

mutable or immutable definition: In the case of constant ID and type, data with variable values is a mutable type. Id,type,value Immutable types

Listing list:

Attributes: The elements in the list can be arbitrarily deleted and the list's ID and type will not change, and ist is a mutable type. All elements in the list can be either an int or a list (a child list). The values in lists are ordered.

Define a list:

L = [1, ' abc ', [3, ' a ']]

Value: Value by index

Print (L[0],l[2][0])

Cycle: Liang

#!/usr/bin/env python#-*-coding:utf-8-*-l=[1,2,3,[4,5]]count=0 whileCount <Len (l):Print(L[count]) Count+=1L=[1,2,3,[4,5]] forCountinchRange (len (l)):ifType (L[count]) islist:         forIinchRange (len (l[count)):Print(L[count][i])Else:        Print(L[count])

List Common actions:

Slice:

l = [' Hello ', ' n ', ' abc ', 343, ' PPP ']
Print (L[1:3])

D:\Python\Python36-32\python.exe e:/python/123.py
[' ABC ']

Process finished with exit code 0

Additional:

l = [' Hello ', ' n ', ' abc ', 343, ' PPP ']
L.append (' Add_1 ')
L.append (' add_2 ')
L.append (' Add_3 ')
Print (L)

D:\Python\Python36-32\python.exe e:/python/123. py['hello'ABC  'PPP''add_1'add_2  'add_3']process finished with exit code 0

Insert:

l = [' Hello ', ' n ', ' abc ', 343, ' PPP ']
L.insert (0, ' insert_1 ')
Print (L)
L.insert (2, ' insert_2 ')
Print (L)
L.insert (4, ' insert_3 ')
Print (L)

D:\Python\Python36-32\python.exe e:/python/123. py['insert_1','Hello', 12,'ABC', 343,'PPP']['insert_1','Hello','insert_2', 12,'ABC', 343,'PPP']['insert_1','Hello','insert_2', 12,'Insert_3','ABC', 343,'PPP']process finished with exit code 0

Delete:

l = [' Hello ', ' n ', ' abc ', 343, ' PPP ']
Print (L)
L.pop ()
Print (L)
L.pop (2)
Print (L)

D:\Python\Python36-32\python.exe e:/python/123. py['hello'ABC  'PPP'['hello']  ABC', 343['hello', 343]process Finished with exit code 0

Contains:

l = [' Hello ', ' n ', ' abc ', 343, ' PPP ']
Print (in L)
Print (' abc ' in L)
Print (' n ' in L)

D:\Python\Python36-32\python.exe e:/python/123. Pytruetruefalseprocess finished with exit code 0

Show Index Location:

l = [' Hello ', ' n ', ' abc ', 343, ' PPP ']
Print (L)
Print (L.index (12))
Print (L.index (' Hello '))

D:\Python\Python36-32\python.exe e:/python/123. py['hello'ABC  'PPP']10Process finished with exit code 0

Number of calculated elements:

l = [' Hello ', ' n ', ' abc ', 343, ' PPP ']
L.append (' Hello ')
Print (L)
Print (L.count (' Hello '))

D:\Python\Python36-32\python.exe e:/python/123. py['hello'ABC  "PPP"'hello']2  Process finished with exit code 0

Extended list:

l = [' Hello ', ' n ', ' abc ', 343, ' PPP ']
L.extend ([1,2,3,4]) #只能扩展列表, if you need to add dictionaries and tuples to the list, you need to use append
Print (L)

D:\Python\Python36-32\python.exe e:/python/123. py['hello'ABC  'PPP', 1, 2, 3, 4]process finished with exit code 0

remove element: remove element by element name

l = [' Hello ', ' n ', ' abc ', 343, ' PPP ']
L.remove (' abc ') #如果列表有多个元素, only the first one is removed
Print (L)

D:\Python\Python36-32\python.exe e:/python/123. py['hello'PPP  ']process finished with exit code 0

Sequential arrangement:

l=[2,3,1]
L.sort ()
Print (L)

D:\Python\Python36-32\python.exe e:/python/123. py[1, 2, 3]process finished with exit code 0

Reverse list:

L=[' A ', ' C ', ' Alex ']
L.reverse ()
Print (L)

D:\Python\Python36-32\python.exe e:/python/123. py['Alex'C  'a']process finished with exit code 0

Meta-group:

Attribute: All elements within a tuple cannot be changed, an element can be any data type

A tuple can contain a list, and the elements in a list in a tuple can be changed. Of course the list can also have tuples.

To define a tuple:

A = (' 1 ', ' 2 ', ' 3 ', [' s ', ' B '])

To change the elements of a list in a tuple:

A[3][0] = ABC

Value:

Print (A[0])

Cycle:

t = (' A ', 1, ' B ', 1, (3,4))
n = 0
While n < len (t):
Print (T[n])
n + = 1

For I in range (len (t)):
Print (T[i])

Common operations for tuples:

Count:

t = (' A ', 1, ' B ', 1, (3,4))
Print (T.count (1))

D:\Python\Python36-32\python.exe e:/python/123. py2Process finished with exit code 0

Index location:

t = (' A ', 1, ' B ', 1, (3,4))
Print (T.index (' B '))

D:\Python\Python36-32\python.exe e:/python/123. py2Process finished with exit code 0

Slice:

t= (' A ', 1, ' B ', 1, (3,4))
Print (T[1:3])

D:\Python\Python36-32\python.exe e:/python/123. PY ('b') Process finished With exit code 0

Contains:

t= (' A ', 1, ' B ', 1, (3,4))
Print (' A ' in t)

D:\Python\Python36-32\python.exe e:/python/123. Pytrueprocess finished with exit code 0

　　　　

　　　　

　　　　　　

Python Foundation day-3