Lecture 17 — Data from Files and Web Pages
==============================================

Overview
--------

-  Review of string operations

-  Files on your computer

   -  Opening and reading files

   -  Closing

   -  Writing files

-  Accessing files across the web

-  Parsing basics

-  String Operations


Opening and Reading Files
----------------------------

-  Given the name of a file as a string, we can open it to read::

       f = open('abc.txt')

   This is the same as:

   ::

       f = open('abc.txt', 'r')

   -  Variable ``f`` now “points” to the first line of file ``abc.txt``.

   -  The ``'r'`` tells Python we will be reading from this file — this
      is the default.

-  
Reading the Contents of a File
------------------------------

-  The most common way to read a file is illustrated in the following
   example that reads each line from a file and prints it on the screen:

   ::

      f = open('abc.txt')
      for line in f:
          print(line)

   (Of course you can replace the call to :func:`print` with any other
   processing code since each ``line`` is just a string!)

-  You can combine the above steps into a single for loop:

   ::

       for line in open('abc.txt'):
           print(line)


Closing and Reopening Files
----------------------------

-  The code below opens, reads, closes, and reopens a file:

   ::

       f = open('abc.txt')

       # Insert whatever code is need to read from the file 
       # and use its contents ...

       f.close()
       f = open('abc.txt')

-  ``f`` now points again to the beginning of the file.

-  This can be used to read the same file multiple times.


Lecture Slides
--------------
https://drive.google.com/file/d/1VN-fEvrzQfAxwn9dwKMGrHbwQervb3RL/view?usp=sharing


Lecture Video
-------------

https://www.youtube.com/watch?v=kl9voiFN-0s