豆瓣电影top250爬虫

中秋3天假，学习了两天爬虫，之前在mooc上跟着昊天老师的课程学过一些，豆瓣电影top250是公认的容易爬取的网站，所以参考着众多实战案例自己写了一遍，自己写各种踩坑，总算集各家之长，写出一个比较满意的半成品，先放在简书中。
写爬虫一定要把框架打好，把爬取网页、解析网页、存储数据、判定目录文件是否存在这几部分分开，各用一个函数，对于分块攻克以及检查、通用替换等都非常有好处。
爬取网页用的是昊天老师的通用框架，强力推荐这个框架。
用的这几个库中，requests用于拉回网页内容、bs4进行网页内容解析、os用于判定、删除和建立文件及文件夹、time用于延时减轻服务器压力。

# import library
import requests
from bs4 import BeautifulSoup
import os
import time

# get html text function
def fGetHtmlText(vUrl):
    try:
        vHeaders = {"user-agent": "Mozilla/5.0", "Host": "movie.douban.com"}
        r = requests.get(vUrl, headers = vHeaders)
        r.raise_for_status()
        r.encoding = r.apparent_encoding
        return(r.text)
    except:
        print("There is something wrong")

# analysis the html text with bs4
def fSoup(vHtml):
    vSoup = BeautifulSoup(vHtml, "html.parser")
    vLis = vSoup.select("ol li")    
    for vLi in vLis:
        # index
        vIndex = vLi.find("em").text
        # title
        vTitle = vLi.find("span", class_= "title").text
        # comment, and replace the unleagel string
        vComment = vLi.find("span", class_ ="inq").text
        vComment = vComment.replace("\u22ef", "")
        # rating num
        vRatingNum = vLi.find("span", class_ = "rating_num").text
        fSvaeToFile(vIndex, vTitle, vComment, vRatingNum)

# judgeing if there is the file and folder
def fJudgeFile():
    if os.path.exists("F:\\PythonData") == False:
        os.mkdir("F:\\PythonData")
    if os.path.exists("F:\\PythonData\\douban.csv") == True:
        os.remove("F:\\PythonData\\douban.csv")

# save data
def fSvaeToFile(index, title, comment, ratingNum):
    f = open('F:\\PythonData\\douban.csv', 'a')
    f.write(f'{index}, {title}, {comment}, {ratingNum}\n')
    f.closed
    
# main function
def main(vUrl):    
    vHtml = fGetHtmlText(vUrl)
    vSoup = fSoup(vHtml)
    
# judge if the file exist and run the main function
fJudgeFile()
for i in range(1):    
    vUrl = "http://movie.douban.com/top250?start=" + str(25)
    print("***正在爬取第" + str(i + 1)+ "页***")
    main(vUrl)
    time.sleep(2)
print("*****爬取完毕*****")