Sort field doesn't work

[fspv]

I set the sort field to 3 digits string at the moment: https://github.com/prius/leetcode-anki/blob/master/generate.py#L298

But the sorting is still incorrect.

For example, there are 15 cards for which sorting by the sort field gives the following order:

012
010
025
011
023
006
002
035
008
033
036
037
037
011
048

So effective there is no sorting.

I guess I need to look at Anki's source code to understand how it uses this field.