Lukas' Weblog

Yesterday (or today in my timezone) Guido wrote a reply, which indicated that he wants python to become one-based. I have written recently about my WTF-situation when I realized that SQL is one-based (and also Lua which comes up in the python’s mailing list discussion). Personally speaking I think that python is that damn intuitive because it’s based on mathematical principles (which Guido as mathematician is aware of). But math is not that consistent and beautiful that it solves all problems.

A sequence of numbers is a range of numbers from x to y with x included but y excluded. To get all indizes of a list, you can use range(0, len(seq)). This is damn readable and does not include a nasty -1 like in most other languages. Well… life is not that beautiful. If we change to a one-based numbering system, what will happen? range(1, len(seq)+1)? Seriously? Lua does not exclude y and therefore does not have a nasty +1.

Lists start with 0, because 0 is the firstzeroth number. In a decimal system, the firstzeroth number with two digits is 10. Three digits: 100. The least-significant number is always zero. The firstzeroth number with one digit is 1? This only comes from an exception in mathematics (10^2..0).

If I want to have all numbers in a list at 2*n indizes in python I will use …

>>> a = [1, 2, 3, 4, 5, 6, 7, 8, 9, 0]
>>> [a[2 * index] for index in xrange(0, len(a) / 2)]
[1, 3, 5, 7, 9]

Again: No nasty +1. Just like Wikipedia points out, it’s about congruence.

I understand that in certain situations it can be useful. If you want to get all numbers at 2ⁿ indizes, you probably want to have the mathematical base⁰=1 and you would be fine with one-based systems. You probably want to get the real firstzeroth number:

>>> import math
>>> a = [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
>>> [a[2 ** index - 1] for index in xrange(0, int(math.log(len(a), 2)) + 1)]
[0, 1, 2, 13]

For Lua it just says:

a = {0, 1, 1, 2, 3, 5, 8, 13, 21, 34}
for index=1,math.log(#a+1, 2)+1 do
  print(a[2 ^ index])
end

I have shown only mathematical examples, but science is want I consider to be one of the most important fields for python. Other (especially old-school) languages really suck at this and it’s one of python’s strengths to be fine with scientists from other fields. In a mathematical context one-based systems it might be okay (see MATLAB), but for me a list starting with 1 is unpythonic and not useful. Yes, just like the Lua community I can live with a one-based languages, but I generally consider it to be a design fault.

Thanks to Bruce Leban for this awesome funny reply.

Update: Guido, you got me. It was a joke

So let’s start with a simple MySQL setup:

mysql> CREATE TABLE example (prefix VARCHAR(50),
domain VARCHAR(30), PRIMARY KEY(prefix, domain));
Query OK, 0 rows affected (0.02 sec)

mysql> INSERT INTO example VALUES
("hello", "world.org"), ("foo", "bar"),  ("Foot","ball");
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0

Alright… so we have some sort of “split up” email addresses. It’s not a problem to combine them together on the fly as far as MySQL provides basic string operations.

mysql> SELECT CONCAT(prefix, "@", domain) as email_addr FROM example;
+-----------------+
| email_addr      |
+-----------------+
| foo@bar         |
| Foot@ball       |
| hello@world.org |
+-----------------+
3 rows in set (0.00 sec)

So now let’s say, we want to remove the Top Level Domain from the domain (“world” instead of “world.org”) [1].

mysql> SELECT SUBSTR(domain, 0, LOCATE('.', domain)-1) as tld FROM example;
+-----+
| tld |
+-----+
|     |
|     |
|     |
+-----+
3 rows in set (0.00 sec)

What? Let’s slow down… take a substring of domain starting at position zero and with length of the position of the “.” (dot character) minus 1 (before that dot character). Okay… so something has to be wrong about it.

mysql> SELECT domain as tld FROM example;
+-----------+
| tld       |
+-----------+
| bar       |
| ball      |
| world.org |
+-----------+
3 rows in set (0.00 sec)

A quarter of an hour later I realized the problem with the help of a colleague:

mysql> SELECT SUBSTR(domain, 1, LOCATE('.', domain)-1) as tld FROM example;
+-------+
| tld   |
+-------+
|       |
|       |
| world |
+-------+
3 rows in set (0.00 sec)

SQL (and therefore the substr function) is one-based. So to address the first character you have to specify it using “1″. MySQL uses 0 to tell “no match”.

Stupid world. Why do we have conventions? To break them? I was aware that MATLAB sucks in this regard too, but I was shocked, when I heard about Lua (both languages one-based).

Note [1]. If you really have such an usecase, please refer to SUBSTRING_INDEX.