By Vasudev Ram
I needed to process some DSV files recently. Here is a Python program I wrote for it, with a few changes over the original. E.g. I do not show the processing of the data here; I only read and print it. Also, I support two different command-line options (and ways) to specify the delimiter character.
DSV (Delimiter-separated values) is a common tabular text data format, with one record per line, and some number of fields per record, where the fields are separated or delimited by some specific character. Some common delimiter characters used in DSV files are tab (which makes them TSV files, Tab-Separated Values, common on Unix), comma (CSV files, Comma-Separated Values, a common spreadsheet and database import-export format), the pipe character (|), the colon (:) and others.
They - DSV files - are described in this section, Data File Metaformats, under Chapter 5: Textuality, of Eric Raymond (ESR)'s book, The Art of Unix Programming, which is a recommended read for anyone interested in Unix (one of the longest-lived operating systems [1]) and in software design and development.
[1] And, speaking a bit loosely, nowaday Unix is also the most widely used OS in the world, by a fair margin, due to its use (as a variant) in Android and iOS based mobile devices, both of which are Unix-based, not to mention Apple MacOS and Linux computers, which also are. Android devices alone number in the billions.
The program, read_dsv.py, is a command-line utility, written in Python, that allows you to specify the delimiter character in one of two ways:
- with a "-c delim_char" option, in which delim_char is an ASCII character,
- with a "-n delim_code" option, in which delim_code is an ASCII code.
It then reads either the files specified as command-line arguments after the -n or -c option, or if no files are given, it reads its standard input.
Here is the code for read_dsv.py:
Here are test runs of the program (both valid and invalid), and the results of each one:
Run it without any arguments. Gives a brief usage message.
Run it with a -h option (for help). Gives the verbose usage message.
Run it with a -v option (invalid run). Gives the brief usage message.
Run it with a -c option but no ASCII character argument (invalid run). Gives the brief usage message.
Run it with a -c option followed by the pipe character (invalid run). The OS (here, Windows) gives an error message because the pipe character cannot be used to end a pipeline.
Run it with the -c option and the pipe character as the delimiter character, but protected (by double quotes) from interpretation by the OS shell (CMD).
Run it with the -n option followed by 124, the ASCII code for the pipe character as the delimiter.
Copy file1.dsv to file3.dsv. Change all the pipe characters (delimiters) to colons:
Run it with the -n option followed by 58, the ASCII code for the colon character.
I added support for the -n option to the program because it makes it more flexible, since you can specify any ASCII character as the delimiter (that makes sense), by giving its ASCII code.
And of course, to find out the values of the ASCII codes for these delimiter characters, I used the char_to_ascii_code.py program from my recent post:
Trapping KeyboardInterrupt and EOFError for program cleanup
You may have noticed that I mentioned delimiter characters and DSV files in that post too. The char_to_ascii_code.py utility shown in that post was created to find the ASCII code for any character (without having to look it up on the web each time).
- Enjoy.
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