Python Essential Reference, Second 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. 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: ...