Linux/Unix > Python Essential Reference, Second Edition > 1. A Tutorial Introduction > File Input and Output | See All Titles

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### 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. The empty string is returned at the end of the file. To make the output of a program go to a file, you can give the file to the `print` statement using `>>` as shown in the following example:

    f = open("out","w")     # Open file for writing
    while year <= numyears:
            principal = principal*(1+rate)
            print >>f,"%3d %0.2f" %% (year,principal)
            year += 1
    f.close()

In addition, files support a `write()` method that can be used to write raw data. For example, the `print` statement in the previous example could have been written this way:

    f.write("%3d   %0.2f\n" % (year,principal))

| Last updated on 3/28/2002 Python Essential Reference, Second Edition, © 2002 New Riders Publishing

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© 2002, O'Reilly & Associates, Inc.