实战爬取

Python Web 爬取

Thomas Laetsch

Data Scientist, NYU

DataCamp 站点

https://www.datacamp.com/courses/all

Div 里有什么？

# response loaded with HTML from https://www.datacamp.com/courses/all

course_divs = response.css('div.course-block')

print( len(course_divs) )
>>> 185

检查 course-block

first_div = course_divs[0]

children = first_div.xpath('./*')

print( len(children) )
>>> 3

第一个子元素

first_div = course_divs[0]

children = first_div.xpath('./*')

first_child = children[0]

print( first_child.extract() )
>>> <a class=... />

第二个子元素

first_div = course_divs[0]

children = first_div.xpath('./*')

second_child = children[1]

print( second_child.extract() )
>>> <div class=... />

被忽略的子元素

first_div = course_divs[0]

children = first_div.xpath('./*')

third_child = children[2]

print( third_child.extract() )
>>> <span class=... />

列表化

使用一个 CSS 定位器

links = response.css('div.course-block > a::attr(href)').extract()

分步提取

# 第 1 步：课程块
course_divs = response.css('div.course-block')

# 第 2 步：超链接元素
hrefs = course_divs.xpath('./a/@href')

# 第 3 步：提取链接
links = hrefs.extract()

拿到课程链接

for l in links:
    print( l )

>>> /courses/free-introduction-to-r
>>> /courses/data-table-data-manipulation-r-tutorial
>>> /courses/dplyr-data-manipulation-r-tutorial
>>> /courses/ggvis-data-visualization-r-tutorial
>>> /courses/reporting-with-r-markdown
>>> /courses/intermediate-r
...

链接已获取

Python Web 爬取