• python关键字和保留字 在Python中yield关键字 (yield Keyword in Python) When we write a function which should perform some operation and provide some result back, we generally use the return statement ...


    When we write a function which should perform some operation and provide some result back, we generally use the return statement for returning the result.


    The yield keyword in python is also used to return a value from a function(just like return) but this keyword also maintains the state of the local variables of the function and when the function is called again, the execution is started from the yield statement executed last time.


    Let's see a simple example and try to understand what yield keyword actually does:


    def counter():
        x = 0
        while x < 5:
            yield x
            # incrementing the value of x
            x += 1

    In the code above we have defined a simple function which has a while loop and is yielding the current value of x and then increments it.


    First things first, when we use a yield statement in a function then the function is called as Generator, about which we will learn in the next tutorial.

    首先,当我们在函数中使用yield语句时,该函数称为Generator ,我们将在下一个教程中学习该函数。

    A generator generates or yields values and cannot be called like a simple function rather it is called like an iterable i.e. by using a loop, for example a for loop.


    Let's see both the cases,


    # calling the above function directly
    print("Simple function call: ", counter())    # should print 0
    # and now lets use a loop to print values
    print("Now lets try using a loop:")
    for y in counter():

    Simple function call: <generator object counter at 0x7f95fba4ba98> Now lets try using a loop: 0 1 2 3 4

    简单函数调用:<位于0x7f95fba4ba98的发电机对象计数器>现在让我们尝试使用循环:0 1 2 3 4

    关于yield关键字要记住的几点 (Some Points to Remember about yield Keyword)

    Think of yield keyword as a smart return statement which remembers what it did the last time and continues from there the next time.


    Like in the counter() function above, when we call it the first time, it will return 0, but when we call it next time, it will increment the value of x and then return 1, then we call it again, it will again increment the value of x and retun the result 2 and so on until the loop is completed.

    就像上面的counter()函数一样,当我们第一次调用它时,它将返回0 ,但是当我们下次调用它时,它将递增x的值,然后返回1 ,然后再次调用它,它将再次增加x的值并重新调整结果2 ,依此类推,直到循环完成。

    1. When we use yield keyword to return data from a function it starts storing the states of the local variable as a result the overhead of memory allocation for the variable in consecutive calls is saved.


    2. Also, in consecutive calls the flow starts from the last yield statement executed which saves time.


    3. We can easily create iterable functions using yield keyword.


    时间来一些例子! (Time for some Examples!)

    As we mentioned above, by using the yield keyword we make our function an iterable. And we know that for an iterable, we can use the next() method for iterating to the next element. So let's try to implement that in our first example.

    如上所述,通过使用yield关键字,我们使函数可迭代。 而且我们知道,对于可迭代对象,我们可以使用next()方法迭代到下一个元素 。 因此,让我们尝试在第一个示例中实现它。

    Example 1:



    In the example above, we have used multiple yield statement to save the state of the execution of the function(or generator) new_gen() such that the next time that function is called the execution begins from where it last left.

    在上面的示例中,我们使用了多个yield语句来保存函数(或生成器) new_gen()的执行状态,以便下次调用该函数时,从该函数的上次离开位置开始执行。

    Try adding one more print(next(x)) statement to the above code and you will see the StopIteration exception which an iterator returns when there is no more data left to iterate over.


    Example 2:


    In this code example we will be using yield keyword in a function to count the occurence of a word in a sentence.



    Using the yield keyword in above problem will help us simplify the code for searching a word in a list of words and increasing the count at the same time because yield keyword will remeber the last state and hence it will not iterate over the words which are already checked.


    Similarly there are many use cases of the yield keyword. In our next tutorial we will learn about Generators which are the functions in which we use yield keyword. In the code example above, count_words is a generator.

    同样, yield关键字有很多用例。 在我们的下一个教程中,我们将学习生成器 ,这些函数是我们使用yield关键字的函数。 在上面的代码示例中, count_words是一个生成器。

    翻译自: https://www.studytonight.com/python/python-yield-keyword


  • 我的python入门代码 这是我学习python的第一个代码 print('hello world')#输出hello word #这是我的第一个程序 print('Hello world')#向控制台输出hello world 这是我自己写的第一个代码。



    print('hello world')#输出hello word
    print('Hello world')#向控制台输出hello world


    if age>=18:
    if age<18:


    关键字:是 python已经使用了的标识符,所以不允许开发者自己定义和关键字相同的标识符。


    其实学习python并没有我们想象中的难,他可以算是众多编程语言中简单的,只要我们用心学,都可以掌握的,把自己的心静下来,不急躁,相信我们总可以掌握。正如“龟叔”的那句话:Life is shot,you need Python(人生苦短,我用python)在这里插入图片描述

  • s) print m.groups() The output is just: "is" But I want to get all the words and punctuations that comes after the word "name". 解决方案 Instead of using regexes you could just (for example) separate...

    I want to find words that appear after a keyword (specified and searched by me) and print out the result. I know that i am suppose to use regex to do it, and i tried it out too, like this:

    import re

    s = "hi my name is ryan, and i am new to python and would like to learn more"

    m = re.search("^name: (\w+)", s)

    print m.groups()

    The output is just:


    But I want to get all the words and punctuations that comes after the word "name".


    Instead of using regexes you could just (for example) separate your string with str.partition(separator) like this:

    mystring = "hi my name is ryan, and i am new to python and would like to learn more"

    keyword = 'name'

    before_keyword, keyword, after_keyword = mystring.partition(keyword)

    >>> before_keyword

    'hi my '

    >>> keyword


    >>> after_keyword

    ' is ryan, and i am new to python and would like to learn more'

    You have to deal with the needless whitespaces separately, though.

  • python 标识符和关键字

    2018-02-02 08:46:37
    1.python标识符 python 标识符是由数字,字母和下划线(_)组合而成,但是不能用数字开头,且区分大小写。例如,5ab 是不合法的一个变量标识符,Sum 和sum是两个不同的变量标识符,_ab, a_b,ab...关键字(key word)是py


    python 标识符是由数字,字母和下划线(_)组合而成,但是不能用数字开头,且区分大小写。例如,5ab 是不合法的一个变量标识符,Sum 和sum是两个不同的变量标识符,_ab, a_b,ab_, a5b, ab5,都是合法的标识符。


    2.python 关键字

    关键字(key word)是python系统定义好的,有特殊含义的标识符,有特殊用途,用户不能自定义的标识符。

    可以用import导入关键字(key word),用print(keyword.kwlist)查看所有关键字

  • and:逻辑‘与’ or:逻辑‘或’ not:逻辑‘非’ del:操作列表,用于删除列表一个或连续几个元素 from:导入相应的模块:from…import… while:while循环,,用于重复执行某一模块,无限循环一般用while ...
  • 参考一个微信开发的代码,通过关键字关联到函数去执行,我运行后 刚刚测试居然好使,发出来大家讨论下有啥优化的地方!代码如下# -*- coding: utf-8 -*-# python3.6# 小程序获取二维码示例from bottle import ...
  • ''' 爬取指定关键字图片 ''' import re# 正则表达式,解析网页 import requests# ...word, lastNum,)#本条语句执行一次获取60张图 文件层次: 参考:爬虫:根据关键词爬取图片 Python爬虫实战教程:批量爬取某网站图片
  • 马上注册,结交更多好友,享用更多功能^_^.../usr/bin/env python# -*- coding:utf-8 -*-import osimport win32comfrom win32com.client import Dispatch# 处理Word文档的类class RemoteWord:def __init__(self, fi...
  • 经常使用百度搜索一些资料,故用Python模拟发送请求。!/usr/bin/env python# coding=utf8#####################name : bd.pyauthor: jaysonzhangdate : 2013-08-04#####################import urllib2import string...
  • 输入关键字可以查找与之相关的关键字。 import requests, re from bs4 import BeautifulSoup def getHTMLText(url): try: kv = {"User-Agent": "Mozilla/5.0"} r = requests.get(url, headers=kv) r....
  • 'queryWord' : keyword, 'cl' : 2 , 'lm' : - 1 , 'ie' : 'utf-8' , 'oe' : 'utf-8' , 'adpicid' : '' , 'st' : - 1 , 'z' : '' , 'ic' : 0 , 'word' : keyword, 's' : '' , 'se' : '...
  • Python3 根据关键字爬取百度图片

    万次阅读 2017-07-18 11:16:27
    运行环境 Python3.6.0 写该脚本的原因:获取图片 创作过程有参考 源码# coding:utf-8 import requests import os import re # import json import itertools import urllib import sys# 百度图片URL解码 # http://
  • x.sort() y.sort() #绘制结果图 plt.plot(x,y) plt.show() except Exception as e: print(e) 3,运行结果 到此这篇关于Python爬虫分析微博热搜关键词的文章就介绍到这了,更多相关Python爬虫微博热搜内容请搜索脚本之...
  • 主要使用python-docx 与pandas 因为python-docx对表格的解析不够友好且效率低,故需转换一次 代码如下 # coding:utf-8 import os, re import docx from docx.document import Document as dc from docx.oxml....
  • python我们可以抓取网页,表格,JSON这种半结构化的数据,那么word文档中的内容这种非结构化的数据我们如何抓取呢。今天我来教大家如何实现python对docx类型的文档中数据的读取,并根据关键字提取相应的内容,然后...
  • 序 原文地址: Python 简单关键字爬取公众号文章 ...关键字搜索、页数 查看cookie 查看token 本文部分参考该博友的文章: https://blog.csdn.net/wnma3mz/article/details/78570580
  • 所以写了一个去漏洞库平台通过关键字爬取数据生成日志文件,这三个平台,就美国国家信息安全漏洞库地址会时不时出现超时情况。若出现超时,可多试两次,三个平台检索出的漏洞差不多,写的不好,仅供参考 python版本...
  • 1.当一个函数中带有yield关键字之后,这个函数就变成了一个生成器。当我们直接调用它时,返回的是一个生成器对象。 2.那么既然它是一个生成器,那么我们可以通过循环来调用它,来执行它内部的逻辑。那么关键来了,带...
  • build a mapping from every word to a number that correlates with how rare that word is. Bonus points for doing it for larger n-grams as well. By combining the idf values of each word in your input ...
  • 原博文2017-12-14 20:37 −1.*args args是非关键字参数,可以理解为形参,为了方便记忆我理解它是arguments的缩写。 2.*kwargs kwargs是键值对参数,为了方便记忆我理解它是key word arguments的缩写。 3.setattr() ...
  • )我这篇文章将简单记录一下python关键字yield的用法。因为写代码需要,我看到了别人的部分代码中有用到yield关键字。作为习惯了C类语言的人,第一次看到这种关键字会感到很迷茫,不知道是用来做什么的,可是偏偏很多...



1 2 3 4 5 ... 20
收藏数 18,094
精华内容 7,237


python 订阅