Python网络资源 + Python Manual

urllib2.urlopen(url[, data][, timeout])Open the URL url, which can be either a string or a Request object.
Warning

HTTPS requests do not do any verification of the server’s certificate.

data may be a string specifying additional data to send to the server, or None if no such data is needed. Currently HTTP requests are the only ones that use data; the HTTP request will be a POST instead of a GET when the data parameter is provided. data should be a buffer in the standard application/x-www-form-urlencoded format. The urllib.urlencode() function takes a mapping or sequence of 2-tuples and returns a string in this format. urllib2 module sends HTTP/1.1 requests withCONNECTION:CLOSEheader included.

The optional timeout parameter specifies a timeout in seconds for blocking operations like the connection attempt (if not specified, the global default timeout setting will be used). This actually only works for HTTP, HTTPS and FTP connections.

This function returns a file-like object with two additional methods:

geturl() — return the URL of the resource retrieved, commonly used to determine if a redirect was followed

info() — return the meta-information of the page, such as headers, in the form of an mimetools.Message instance (see Quick Reference to HTTP Headers)

Raises URLError on errors.

Note that None may be returned if no handler handles the request (though the default installed global OpenerDirector uses UnknownHandler to ensure this never happens).

In addition, default installed ProxyHandler makes sure the requests are handled through the proxy when they are set.

Changed in version 2.6: timeout was added.