Tab-delimited files are text files organized around data that has rows and columns. This format is used to exchange data between spread-sheet programs or databases. A tab-delimited file uses just rwo punctuation rules to encode the data.

In the ideal cases, a CSV file will have the same number of columns in each row, and the first row will be column titles. Almost as pleasant is a file without column titles, but with a known sequence of columns. In the more complex cases, the number of columns per row varies.

When we have a single, standard punctuation mark, we can simply use two operations in the string and list classes to process files. We use the split method of a string to parse the rows. We use the join method of a list to assemble the rows.

We don't actually need a separate module to handle tab-delimited files. We looked at a related example in the section called “Reading a Text File”.

Reading. The most general case for reading Tab-delimited data is shown in the following example.

myFile= open( "
somefile
", "rU" )
for aRow in myFile:
    print aRow.split('\t')
myFile.close()

Each row will be a list of column values.

Writing. The writing case is the inverse of the reading case. Essentially, we use a "\t".join( someList ) to create the tab-delimeted row. Here's our sailboat example, done as tab-delimited data.

test= file( "boats.tab", "w" )
test.write( "\t".join( Boat.csvHeading ) )
test.write( "\n" )
for d in db:
    test.write( "\t".join( map( str, d.csvRow() ) ) )
    test.write( "\n" )
test.close()

Note that some elements of our data objects aren't string values. In this case, the value for sails is a tuple, which needs to be converted to a proper string. The expression map(str, someList ) applies the str function to each element of the original list, creating a new list which will have all string values. See the section called “Sequence Processing Functions: map, filter, reduce and zip”.