RE在pythex中工作，但在python中不工作。

Question

我正在做一个任务，我需要从现场抓取信息。

为此，我正在使用https://www.nintendo.com/games/nintendo-switch-bestsellers，并需要刮的游戏标题，价格，然后图像来源。我有标题工作，但价格和图像来源只是调整空的名单，虽然当通过pythex它返回正确的答案。

这是我的代码：

from re import findall, finditer, MULTILINE, DOTALL
from urllib.request import urlopen

game_html_source = urlopen\
('https://www.nintendo.com/games/nintendo-switch-bestsellers').\
read().decode("UTF-8")

# game titles - working
game_title = findall(r'<h3 class="b3">([A-Z a-z:0-9]+)</h3>', game_html_source)
print(game_title)

# game prices - retuning empty-list
game_prices = findall(r'<p class="b3 row-price">(\$[.0-9]+)</p>', game_html_source)
print(game_prices)

# game images - returning empty list
game_images = findall(r'<img alt="[A-Z a-z:]+" src=("https://media.nintendo.com/nintendo/bin/[A-Za-z0-9-\/_]+.png")>',game_html_source)
print(game_images)

Answer 1

使用regex解析HTML有太多的缺陷，难以进行可靠的处理。BeautifulSoup和其他HTML解析器的工作方式是构建一个完整的文档数据结构，然后导航它来提取有趣的部分--它是彻底的和全面的，但是如果源中有一些错误的HTML，即使它位于您不关心的部分，它也可以击败解析过程。parsing采用了一种中间的方法--您可以定义与您想要的部分匹配的迷你解析器，并跳过其他所有内容(这也简化了解析后的导航)。为了解决HTML样式中的某些变化，pyparsing提供了一个函数makeHTMLTags，它为开始标记和结束标记返回一对pair解析表达式：

foo_start, foo_end = pp.makeHTMLTags('foo')

foo_start将匹配：

<foo>
<foo/>
<foo class='bar'>
<foo href=something_not_in_quotes>

还有更多的属性和空格的变化。

foo_start表达式(就像所有return解析表达式一样)将返回一个ParseResults对象。这使得访问解析标记的各个部分变得非常容易：

foo_data = foo_start.parseString("<foo img='bar.jpg'>")
print(foo_data.img)

有关任天堂页面刮刀，请参见下面的注释源：

import pyparsing as pp

# define expressions to match opening and closing tags <h3>
h3, h3_end = pp.makeHTMLTags("h3")

# define a specific type of <h3> tag that has the desired 'class' attribute
h3_b3 = h3().addCondition(lambda t: t['class'] == "b3")

# similar for <p>
p, p_end = pp.makeHTMLTags("p")
p_b3_row_price = p().addCondition(lambda t: t['class'] == "b3 row-price")

# similar for <img>
img, _ = pp.makeHTMLTags("img")
img_expr = img().addCondition(lambda t: t.src.startswith("//media.nintendo.com/nintendo/bin"))

# define expressions to capture tag body for title and price - include negative lookahead for '<' so that
# tags with embedded tags are not matched
LT = pp.Literal('<')
title_expr = h3_b3 + ~LT + pp.SkipTo(h3_end)('title') + h3_end
price_expr = p_b3_row_price + ~LT + pp.SkipTo(p_end)('price') + p_end

# compose a scanner expression by '|'ing the 3 sub-expressions into one
scanner = title_expr | price_expr | img_expr

# not shown - read web page into variable 'html'

# use searchString to search through the retrieved HTML for matches
for match in scanner.searchString(html):
    if 'title' in match:
        print("Title:", match.title)
    elif 'price' in match:
        print("Price:", match.price)
    elif 'src' in match:
        print("Img src:", match.src)
    else:
        print("???", match.dump())

印出来的第一批火柴如下：

Img src: //media.nintendo.com/nintendo/bin/SF6LoN-xgX1iT617eWfBrNcWH6RQXnSh/I_IRYaBzJ61i-3hnYt_k7hVxHtqGmM_w.png
Title: Hyrule Warriors: Definitive Edition
Price: $59.99
Img src: //media.nintendo.com/nintendo/bin/wcfCyAd7t2N78FkGvEwCOGzVFBNQRbhy/AvG-_d4kEvEplp0mJoUew8IAg71YQveM.png
Title: Donkey Kong Country: Tropical Freeze
Price: $59.99
Img src: //media.nintendo.com/nintendo/bin/QKPpE587ZIA5fUhUL4nSbH3c_PpXYojl/J_Wd79pnFLX1NQISxouLGp636sdewhMS.png
Title: Wizard of Legend
Price: $15.99