Python Full Stack development 14

Advantages of iterators:
1. Save Memory
2. Inertia mechanism
3. Unidirectional, irreversible
How to tell if it is an iterative object and an iterator

　　Iterators that iterate over an object

Iterative Object __iter__ (): It becomes an iterator
1. ' __iter__ ' in Dir (obj): True or Flase, returns true to represent that he is an iterative object
　　　　2. Introduction of Modules
From collections Import Iterator (iterator)
Print (isinstance (parameter name, Iterator)
From collections import iterable (Iteration object)
Print (isinstance (parameter name, Itera) ble
　　Generator:
An iterator that writes its own Python code is the generator.
The generator itself is an iterator
Generator expressions and lists push-down
1. List-derived
[Variable (processed variable) for variable in iterable (Iteration object)] # loop mode
[Variable (processed variable) for variable in iterable if condition]# filter mode
2. Generator expression: Just like the list expression, the parentheses are different.

(Variable (processed variable) for variable in iterable (Iteration object)) # Loop mode
(Variable (processed variable) for variable in iterable if condition) # Filter Mode

Pros: 1. Save code
Cons: Bad troubleshooting
Overall: Generally used in a list deduction structure, in other ways can also, very complex list, list derivation is not constructed

Built-in functions

1.1 Scope-related

A =33b = 22def func ():    a = 1    print (Globals (), ' \ n ', locals ()) func ()

1.21 Other related

Execution of String type code Eval,exec,complie

Print (eval (' 1*2*3*4*5*6*7*8*9 ')) Li = "" For I in Range:    print (i) "" "Exec (LI)

1.22 input and output related print and input

k = Print (1,2,4,6,sep= ' ****** ', end= ') with open (' Test. txt ', ' w ', encoding= ' utf-8 ') as F:    print (' 111111111111 ', 1111 , file=f,sep= ' * * * * ') print ('    111111111111 ', 1111,file=f,sep= ')    print (' 111111111111 ', 1111,file=f,sep= ‘****‘)

1.23 memory-related hash (): Gets the hash value of a hash object, ID (return memory address)

Print (hash (1020000000000000000)) # number up to 19 to guarantee that the hash value is the same as the value, and it becomes another print (hash (' 1111111111111111111 ')) # hash string print ( Hash ((1,2,3,4)) # Hashion Group print (hash (True)) # hash bool Value

The Open: function opens a file, creates a Files object, and the related method can call it to read and write 1.25 help (): Helps a = 1help (a) #查看帮助

1.26 Call related callable () can call return true cannot call return False

Press CTRL + C to copy the code<textarea></textarea>Press CTRL + C to copy the code

Python Full Stack development 14