逻辑流程 - 尝试使用 BeautifulSoup 和 CSV Writer 遍历网站页面

Question

我似乎无法找出合适的 indents/clause 位置来让它循环超过 1 页。此代码当前可以很好地打印出 CSV 文件，但只打印第一页。

#THIS WORKS BUT ONLY PRINTS THE FIRST PAGE

from bs4 import BeautifulSoup
from urllib2 import urlopen
import csv

page_num = 1
total_pages = 20

with open("MegaMillions.tsv","w") as f:
    fieldnames = ['date', 'numbers', 'moneyball']
    writer = csv.writer(f, delimiter = '\t')
    writer.writerow(fieldnames)

    while page_num < total_pages:
        page_num = str(page_num)
        soup = BeautifulSoup(urlopen('http://www.usamega.com/mega-millions-history.asp?p='+page_num).read())

    for row in soup('table',{'bgcolor':'white'})[0].findAll('tr'):

        tds = row('td')
        if tds[1].a is not None:
            date = tds[1].a.string.encode("utf-8")
            if tds[3].b is not None:
                uglynumber = tds[3].b.string.split()
                betternumber = [int(uglynumber[i]) for i in range(len(uglynumber)) if i%2==0]
                moneyball = tds[3].strong.string.encode("utf-8")

                writer.writerow([date, betternumber, moneyball])
        page_num = int(page_num)
        page_num += 1

print 'We\'re done here.'

当然，这只会打印最后一页：

#THIS WORKS BUT ONLY PRINTS THE LAST PAGE

from bs4 import BeautifulSoup
from urllib2 import urlopen
import csv

page_num = 1
total_pages = 20

while page_num < total_pages:
    page_num = str(page_num)
    soup = BeautifulSoup(urlopen('http://www.usamega.com/mega-millions-history.asp?p='+page_num).read())

    with open("MegaMillions.tsv","w") as f:
        fieldnames = ['date', 'numbers', 'moneyball']
        writer = csv.writer(f, delimiter = '\t')
        writer.writerow(fieldnames)

        for row in soup('table',{'bgcolor':'white'})[0].findAll('tr'):

            tds = row('td')
            if tds[1].a is not None:
                date = tds[1].a.string.encode("utf-8")
                if tds[3].b is not None:
                    uglynumber = tds[3].b.string.split()
                    betternumber = [int(uglynumber[i]) for i in range(len(uglynumber)) if i%2==0]
                    moneyball = tds[3].strong.string.encode("utf-8")

                    writer.writerow([date, betternumber, moneyball])
        page_num = int(page_num)
        page_num += 1

print 'We\'re done here.'

Answer 1

你的第二个代码示例的问题是你每次都在覆盖你的文件。而不是

open("MegaMillions.tsv","w")

使用

open("MegaMillions.tsv","a")

"a"打开文件进行追加，这就是你想要做的

Answer 2

多亏了这些建议，这里有一个可行的变体：

from bs4 import BeautifulSoup
from urllib2 import urlopen
import csv

page_num = 1
total_pages = 73

with open("MegaMillions.tsv","w") as f:
    fieldnames = ['date', 'numbers', 'moneyball']
    writer = csv.writer(f, delimiter = '\t')
    writer.writerow(fieldnames)

    while page_num <= total_pages:
        page_num = str(page_num)
        soup = BeautifulSoup(urlopen('http://www.usamega.com/mega-millions-history.asp?p='+page_num).read())

        for row in soup('table',{'bgcolor':'white'})[0].findAll('tr'):

            tds = row('td')
            if tds[1].a is not None:
                date = tds[1].a.string.encode("utf-8")
                if tds[3].b is not None:
                    uglynumber = tds[3].b.string.split()
                    betternumber = [int(uglynumber[i]) for i in range(len(uglynumber)) if i%2==0]
                    moneyball = tds[3].strong.string.encode("utf-8")

                    writer.writerow([date, betternumber, moneyball])
        page_num = int(page_num)
        page_num += 1

print 'We\'re done here.'

在 'a' 上选择了这个，因为这样标题行就会被写入每一页。

逻辑流程 - 尝试使用 BeautifulSoup 和 CSV Writer 遍历网站页面

Logic flow - trying to iterate through website pages with BeautifulSoup and CSV Writer

python

csv

beautifulsoup