Python: Essential Reference, Third Edition

File Input and Output

The following program opens a file and reads its contents line by line:

f = open("foo.txt")        # Returns a file object
line = f.readline()        # Invokes readline() method on file
while line:
        print line,        # trailing ',' omits newline character
        line = f.readline()
f.close()

The open() function returns a new file object. By invoking methods on this object, you can perform various file operations. The readline() method reads a single line of input, including the terminating newline. An empty string is returned at the end of the file.

In the example, the program is simply looping over all the lines in the file foo.txt. Whenever a program loops over a collection of data like this (for instance input lines, numbers, strings, and so on), ...