What are the attributes of 'urlretrieve' function in Python?

Question

I want to write a Python program to automatically fill web forms. On searching a lot, i found this code.

import urllib urllib.urlretrieve("http://www.google.com/", "somefile.html", lambda x,y,z:0, urllib.urlencode({"username": "xxx", "password": "pass"}))

This function takes a lot of arguments. Can you please explain what each argument means?

Answer 1

If we take a look at the official Python documentation for urllib.urlretrieve , we get a nice explanation:

Copy a network object denoted by a URL to a local file, if necessary. If the URL points to a local file, or a valid cached copy of the object exists, the object is not copied. Return a tuple (filename, headers) where filename is the local file name under which the object can be found, and headers is whatever the info() method of the object returned by urlopen() returned (for a remote object, possibly cached). Exceptions are the same as for urlopen() .

The second argument, if present, specifies the file location to copy to (if absent, the location will be a tempfile with a generated name). The third argument, if present, is a hook function that will be called once on establishment of the network connection and once after each block read thereafter. The hook will be passed three arguments; a count of blocks transferred so far, a block size in bytes, and the total size of the file. The third argument may be -1 on older FTP servers which do not return a file size in response to a retrieval request.

If the url uses the http: scheme identifier, the optional data argument may be given to specify a POST request (normally the request type is GET ). The data argument must in standard application/x-www-form-urlencoded format; see the urlencode() function below.

Changed in version 2.5: urlretrieve() will raise ContentTooShortError when it detects that the amount of data available was less than the expected amount (which is the size reported by a Content-Length header). This can occur, for example, when the download is interrupted.

The Content-Length is treated as a lower bound: if there's more data to read, urlretrieve() reads more data, but if less data is available, it raises the exception.

You can still retrieve the downloaded data in this case, it is stored in the content attribute of the exception instance.

If no Content-Length header was supplied, urlretrieve() can not check the size of the data it has downloaded, and just returns it. In this case you just have to assume that the download was successful.

By the way, they're called arguments or parameters, not attributes.