如何在Python中根据两个绝对URL构造相对URL

Question

有没有一个内置的函数可以根据一个基础网址，比如 http://www.example.com/faq/index.html，和一个目标网址，比如 http://www.example.com/images.html，来得到像这样的网址：../images.html？

我查看了 urlparse 模块。我想要的其实是 urljoin() 函数的对应功能。

Answer 1

import itertools
import urlparse

def makeRelativeUrl(sourceUrl, targetUrl):
  '''

  :param sourceUrl: a string
  :param targetUrl: a string
  :return: the path to target url relative to first or targetUrl if at different net location
  '''
  # todo test
  parsedSource = urlparse.urlparse(sourceUrl)
  parsedTarget = urlparse.urlparse(targetUrl)

  if parsedSource.netloc == parsedTarget.netloc:
    # if target on same path but lower than source url
    if parsedTarget.path.startswith(parsedSource.path):
      return parsedTarget.path.replace(parsedSource.path, '.')
    # on same path
    elif parsedTarget.path.rsplit('/', 1)[0] == parsedSource.path.rsplit('/', 1)[0]:
      return './' + parsedTarget.path.rsplit('/', 1)[1]
    # same netloc, varying paths
    else:
      path = ''
      upCount = 0
      for item in list(itertools.izip_longest(parsedSource.path.rsplit('/'), parsedTarget.path.rsplit('/'))):
        if item[0] == item[1]:
          pass
        else:
          if item[0] is not None:
            upCount += 1
          if item[1] is not None:
            path += item[1] + '/'
      return upCount * '../' + path
  else:
    return targetUrl


if __name__ == '__main__':
  '''
  "tests" :p
  '''
  url1 = 'http://coolwebsite.com/questions/bobobo/bo/bo/1663807/how-can-i-iterate-through-two-lists-in-parallel-in-python'
  url2 = 'http://coolwebsite.com/questions/126524/iterate-a-list-with-indexes-in-python'

  print url1
  print url2
  print 'second relative to second:'
  print makeRelativeUrl(url1, url2)

  url1 = 'http://coolwebsite.com/questions/1663807/how-can-i-iterate-through-two-lists-in-parallel-in-python'
  url2 = 'http://coolwebsite.com/questions/1663807/bananas'

  print url1
  print url2
  print 'second relative to first:'
  print makeRelativeUrl(url1, url2)

  url1 = 'http://coolwebsite.com/questions/1663807/fruits'
  url2 = 'http://coolwebsite.com/questions/1663807/fruits/berries/bananas'

  print url1
  print url2
  print 'second relative to first:'
  print makeRelativeUrl(url1, url2)

运行'tests'看看它是否能正常工作 :P

Answer 2

首先想到的解决方案是：

>>> os.path.relpath('/images.html', os.path.dirname('/faq/index.html'))
'../images.html'

当然，这需要对网址进行解析 -> 比较域名 (!!) -> 如果需要的话，重写路径 -> 重新添加查询参数和片段。

编辑：一个更完整的版本

import urlparse
import posixpath

def relative_url(destination, source):
    u_dest = urlparse.urlsplit(destination)
    u_src = urlparse.urlsplit(source)

    _uc1 = urlparse.urlunsplit(u_dest[:2]+tuple('' for i in range(3)))
    _uc2 = urlparse.urlunsplit(u_src[:2]+tuple('' for i in range(3)))

    if _uc1 != _uc2:
        ## This is a different domain
        return destination

    _relpath = posixpath.relpath(u_dest.path, posixpath.dirname(u_src.path))

    return urlparse.urlunsplit(('', '', _relpath, u_dest.query, u_dest.fragment)

然后

>>> relative_url('http://www.example.com/images.html', 'http://www.example.com/faq/index.html')
'../images.html'
>>> relative_url('http://www.example.com/images.html?my=query&string=here#fragment', 'http://www.example.com/faq/index.html')
'../images.html?my=query&string=here#fragment'
>>> relative_url('http://www.example.com/images.html', 'http://www2.example.com/faq/index.html')
'http://www.example.com/images.html'
>>> relative_url('https://www.example.com/images.html', 'http://www.example.com/faq/index.html')
'https://www.example.com/images.html'

编辑：现在使用 posixpath 的 os.path 实现，这样在Windows上也能工作。

Answer 3

你可以使用 urlparse.urlparse 来找到路径，使用 os.path.relname 的 posixpath 版本来找到相对路径。

(注意：这个方法在 Linux 系统上有效，但在 Windows 系统上可能不适用)：

import urlparse
import sys
import posixpath

def relurl(target,base):
    base=urlparse.urlparse(base)
    target=urlparse.urlparse(target)
    if base.netloc != target.netloc:
        raise ValueError('target and base netlocs do not match')
    base_dir='.'+posixpath.dirname(base.path)
    target='.'+target.path
    return posixpath.relpath(target,start=base_dir)

tests=[
    ('http://www.example.com/images.html','http://www.example.com/faq/index.html','../images.html'),
    ('http://google.com','http://google.com','.'),
    ('http://google.com','http://google.com/','.'),
    ('http://google.com/','http://google.com','.'),
    ('http://google.com/','http://google.com/','.'), 
    ('http://google.com/index.html','http://google.com/','index.html'),
    ('http://google.com/index.html','http://google.com/index.html','index.html'), 
    ]

for target,base,answer in tests:
    try:
        result=relurl(target,base)
    except ValueError as err:
        print('{t!r},{b!r} --> {e}'.format(t=target,b=base,e=err))
    else:
        if result==answer:
            print('{t!r},{b!r} --> PASS'.format(t=target,b=base))
        else:
            print('{t!r},{b!r} --> {r!r} != {a!r}'.format(
                t=target,b=base,r=result,a=answer))