13.5. Retrieving web pages with urllib

While we can manually send and receive data over HTTP using the socket library, there is a much simpler way to perform this common task in Python by using the urllib library.

Using urllib, you can treat a web page much like a file. You simply indicate which web page you would like to retrieve and urllib handles all of the HTTP protocol and header details.

Q-1: The _______ library is used to simplify sending and receiving data from a web page.

The equivalent code to read the romeo.txt file from the web using urllib is as follows:

import urllib.request fhand = urllib.request.urlopen('http://data.pr4e.org/romeo.txt') for line in fhand: print(line.decode().strip())

Once the web page has been opened with urllib.urlopen, we can treat it like a file and read through it using a for loop.

When the program runs, we only see the output of the contents of the file. The headers are still sent, but the urllib code consumes the headers and only returns the data to us.

Q-3: True or False? The program above shows the headers and contents of the file.

• True
• Try again.
• False
• The urllib code consumes the headers and only returns the data to us - the data being the contents.

As an example, we can write a program to retrieve the data for romeo.txt and compute the frequency of each word in the file as follows:

import urllib.request, urllib.parse, urllib.error fhand = urllib.request.urlopen('http://data.pr4e.org/romeo.txt') counts = dict() for line in fhand: words = line.decode().split() for word in words: counts[word] = counts.get(word, 0) + 1 print(counts)

Again, once we have opened the web page, we can read it like a local file.

Q-5: True or False? The urllib library opens a web page and allows it to be read like a file.

• True
• Correct! urllib makes it possible to treat a web page like a local file.
• False
• Try again.

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