Python generator and application instance parsing, python Generator

Python generator and application instance parsing, python Generator

This article focuses on the Python generator and its application, as follows.

I. Definition

It can be understood as a data type, which automatically implements the iterator protocol (other data types need to call their own built-in _ iter _ method), so the generator is an iteratable object.

2. Two generator forms (Python provides generators in two different ways)

1. Generator function: General function definition. However, use the yield statement instead of the return Statement to return the result. The yield statement returns a result at a time. In the middle of each result, the function state is suspended so that it can continue to be executed next time when it leaves.

Yield features:

1. Execute the function result as an iterator (encapsulate _ iter __,__ next _ in an elegant way __)
2. The status of function pause and re-running is caused by yield

Def func (): print ('first') yield 11111111 print ('second') yield 2222222 print ('third') yield 33333333 print ('Fourth ') g = func () print (g) from collections import Iteratorprint (isinstance (g, Iterator) # determine whether it is an Iterator object print (next (g )) print ('=>') print (next (g )) print ('=>') print (next (g) for I in g: # I = iter (g) print (I)

Note: What is the comparison between yield and return?

• Same: both have the function of returning values.
• Different: return can only return one value, while yield can return multiple values

2. Generator expression: similar to list derivation. However, the generator returns an object that generates results on demand, instead of building a result list at a time.

g=('egg%s' %i for i in range(1000))print(g)print(next(g))print(next(g))print(next(g))with open('a.txt',encoding='utf-8') as f:  # res=max((len(line) for line in f))  res=max(len(line) for line in f)  print(res)print(max([1,2,3,4,5,6]))with open('a.txt',encoding='utf-8') as f:  g=(len(line) for line in f)  print(max(g))  print(max(g))  print(max(g))

Iii. Application

# [{'Name': 'apple', 'price': 333, 'Count': 3},] file Content # complete file reading and operations through the generator interpreter with open('db.txt ', encoding = 'utf-8') as f: info = [{'name': line. split () [0], 'price': float (line. split () [1]), 'Count': int (line. split () [2])} for line in f if float (line. split () [1])> = 30000] print (info)

Summary

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