##
11.5.22 Examples

This example gets the python.org main page and displays the first 100 bytes of it:

    >>> import urllib2
    >>> f = urllib2.urlopen('http://www.python.org/')
    >>> print f.read(100)
    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
    <?xml-stylesheet href="./css/ht2html

Here we are sending a data-stream to the stdin of a CGI and reading the data it returns to us:

    >>> import urllib2
    >>> req = urllib2.Request(url='https://localhost/cgi-bin/test.cgi',
    ...                       data='This data is passed to stdin of the CGI')
    >>> f = urllib2.urlopen(req)
    >>> print f.read()
    Got Data: "This data is passed to stdin of the CGI"

The code for the sample CGI used in the above example is:

    #!/usr/bin/env python
    import sys
    data = sys.stdin.read()
    print 'Content-type: text-plain\n\nGot Data: "%s"' % data

Use of Basic HTTP Authentication:

    import urllib2
    # Create an OpenerDirector with support for Basic HTTP Authentication...
    auth_handler = urllib2.HTTPBasicAuthHandler()
    auth_handler.add_password('realm', 'host', 'username', 'password')
    opener = urllib2.build_opener(auth_handler)
    # ...and install it globally so it can be used with urlopen.
    urllib2.install_opener(opener)
    urllib2.urlopen('http://www.example.com/login.html')

`build_opener()` provides many handlers by default, including a `ProxyHandler`. By default, `ProxyHandler` uses the environment variables named `<scheme>_proxy`, where `<scheme>` is the URL scheme involved. For example, the http_proxy environment variable is read to obtain the HTTP proxy's URL.

This example replaces the default `ProxyHandler` with one that uses programatically-supplied proxy URLs, and adds proxy authorization support with `ProxyBasicAuthHandler`.

    proxy_handler = urllib2.ProxyHandler({'http': 'http://www.example.com:3128/'})
    proxy_auth_handler = urllib2.HTTPBasicAuthHandler()
    proxy_auth_handler.add_password('realm', 'host', 'username', 'password')

    opener = build_opener(proxy_handler, proxy_auth_handler)
    # This time, rather than install the OpenerDirector, we use it directly:
    opener.open('http://www.example.com/login.html')

Adding HTTP headers:

Use the headers argument to the `Request` constructor, or:

    import urllib2
    req = urllib2.Request('http://www.example.com/')
    req.add_header('Referer', 'http://www.python.org/')
    r = urllib2.urlopen(req)

`OpenerDirector` automatically adds a User-Agent: header to every `Request`. To change this:

    import urllib2
    opener = urllib2.build_opener()
    opener.addheaders = [('User-agent', 'Mozilla/5.0')]
    opener.open('http://www.example.com/')

Also, remember that a few standard headers (Content-Length:, Content-Type: and Host:) are added when the `Request` is passed to `urlopen()` (or `OpenerDirector.open()`).