Iterator generators and modules

One 、 iterator

1. What is iterator （iter）

   Iterators are container data types , Multiple data can be saved at the same time , Can be traversed ; It can also be converted into lists and tuples

   When printing an iterator, you cannot print the elements inside ; Iterator not supported len operation

​ If you need elements in the iterator , You must take the element out of the iterator , And once the element is taken out , This element does not exist in the iterator .

2. How to create iterators

   Method 1 ： adopt iter Replace other sequences with iterators

   Method 2 ： Create a generator object （ Generator can be regarded as a special iterator ）

iter1 = iter（'abc'）
print(iter1)
# print(len(iter)) #  Report errors ！

3. Get the elements in the iterator

   1） Get a single element ：next（ iterator ）

   2）for Loop traversal

print(next(iter1))			# 'a'
print(next(iter1))			# 'b'
print(next(iter1))			# 'c'
# print(next(iter1)) #  Report errors ！


for x in iter1:
    print(f'x:{
      x}')
    
    

iter2 = iter([10, 20, 30, 40])
for x in iter2:
    print(f'x:{
      x}')
    
# print(next(iter2)) # StopIteration


iter3 = iter('hello')
print(list(iter3))			# ['h', 'e', 'l', 'l', 'o']
# print(next(iter3)) #  Report errors ！

Two 、 generator

1. generator （generator）

   A generator is a container with the ability to generate multiple data .

   Generators are the same as iterators when getting data .

2. How to create a generator

   Call a with yield Keyword function can get a generator object

   （ If a function has yield, Then this function will not execute the function body when calling , Nor does it get the return value , And get a generator ）

def func1():
    print('=====')
    print('+++++')
    if False:
        yield
        
        
result = func1()
print('result', result)

3. Control the ability of the generator to generate data

   Executing the function corresponding to the generator will encounter several times yield How many data can this generator generate , Every encounter yield When ,yield The following values correspond to the data that can be generated .

def func2():
    yield 100
    for i in range(4):
        yield i


gen2 = func2()
for x in gen2:
    print (f'====:{
      x}')
    
    
def func3():
    yield 100
    yield 200
    yield 300
    
    
print(next(func3()))
print(next(func3()))
print(next(func3()))

gen3 = func3()
print(next(gen3))
print(next(gen3))
print(next(gen3))

 practice 1： Create a generator function , Can be produced before N An even number , Even from 0 Start 
N -> 5  produce ：0, 2, 4, 6, 8
def nums_creater(n: int):
    nums = 0
    for i in range(0, 2*x, 2):
        yield i
        nums += 2
        
        
gen4 = nums_creater(5)
print(next(gen4))
for x in gen4:
    print(x)

4. How the generator generates data

   When getting data through the generator object , The program will execute the function corresponding to the generator , Only execute until yield Will stop , take yield The following data is taken as the data obtained this time , Record the end position , The next time you get data, start from the last end .

def func4():
    print('-------1---------')
    yield 100
    print('-------2---------')
    yield 200
    print('-------3---------')
    yield 300
    print('-------end---------')
    
    
gen5 = func4()
print(gen5)
print(' Take the element :', next(gen5))
for _ in range(5):
    print('+++++++')
    
print(' De element ：', next(gen5))
print(' De element ：', next(gen5))
# print(' De element ：', next(gen5)) #  Report errors ！

3、 ... and 、 modular

1. What is a module

   python In a py File is a module

2. How to use the content of another module in one module

   Be careful ： If you want a module to be used by another module , Then the module name of this module must be an identifier and And not a keyword
   One module can use all global variables in another module , But you must import before using

3. The import module

   import Module name – Import the specified module , Import can be done through ’ Module name .' Use all global variables in the module

   form Module name import Global variables 1, Global variables 2,… - Import the specified module , After importing, you can directly use the specified global variables

   from Module name import * – Import the specified module , After importing, you can directly use all global variables

   import Module name as New module name – Rename the module , Use the new module name when using the module after renaming

   from Module name import Variable name as New variable name – Rename the imported variable

 Import method 1 ：
import test1
print(test1.a)		# 10
print(test1.x)		# 100
test1.func1()		# test1 Function of 


 Import mode 2 ：
from test1 import x, func1
print(x)		# 100
func1()			# test1 Function of 


 Import mode 3 ： Use wildcards *
from test1 import *
print(a)
print(x)
func1()


 Import mode 4 ： Module renaming 
import test1 as test
test1 = 300
print(test1)				# 300
print(test.a, test.x)		# 10 100
test.func1()				# test1 Function of 


 Import method 5 ： Rename the variable 
from test1 import a as a1, x, func1
a = 'abc'
print(a)		# abc
print(a1)		# 10
print(x)		# 100
func1()			# test1 Function of 

4. Principle of import module

   When passed import perhaps from-import When importing a module , The system will automatically execute all the codes in this module

import test1
from test1 import a

Four 、 Use of the bag

1. What is a bag

   A package contains （init.py） File folder

2. Use the contents of the package （ Import ）

   import Package name – Direct import package

   import Package name . modular – Can pass ’ package . modular ’ Use all global variables in the specified module

   from package import modular 1, modular 2, …

   from package . modular import Variable name 1, Variable name 2,…

3. The principle of importing packages

   When importing modules in the package through the package , The program will execute in the package first __init__.py All the codes in the file , Then execute the code in the corresponding module .

1.  Direct import package 
import files


2.  Import modules through packages 
import files.excel
files.excel.read_excel()
print(files.excel)


3.  rename 
import files.excel as f_excel
f_excel.read_excel()
print(f_excel.x)


4.  Import modules through packages 
from files import excel, plist
excel.read_excel()
plist.read_plist()


5.  Import the contents of the module through the package 
from files.excel import read_excel
read_excel()


6.  Directly use the shortcuts in the package 
import files
files.read_excel()

from files import read_excel
read_excel()

import files
files.plist.read_plist()

import files
files.open_file()