Week 2 Learning Summary

Week 2 subject 1: File Operations

• File means text files.  It's a giant leap forward which means you are finally free from keystrokes and can now process something much more complex and more meaningful!

• Always use the open() function to open a file before using, which returns a File object you'll need to refer to whenever you need to operate a file.

• Always use the .close() method to close the file after use.

• Read from files using:

• .read(number of characters)

• .readline()

• Pay attention lines read from a File contain the newline characters at the end of each line.

• You can use File like a list of lines with for l in f: 

• ATTENTION: the File object keeps track of the current position read.  It always moves forward.

• More ways to process File contents in Lists:

• List(File) is a list of lines from File,

• .readlines(hint) returns a list of lines.

• One way to avoid explicitly closing files is using 

        with open(Filename) as File:

            File will be automatically closed at the end of the with block.

• Opening files for output using the 'w' or 'a' modes in the open() function.  Note the different behaviour vs. 'r' when the file doesn't exist.

• Output to files with the write() function.

• Files by default is a sequential media.  There's a historical reason for this.  However there are ways to move in a file in both directions:

• .seek(offset, from) moves forward or backward in file,

• .tell() tells the current position in file.