I am writing some python code to do Order Flow Imbalance analysis from L2 orderbook updates. The language is unimportant: the logic is pretty subtle, so that the main difficulties are not in the language details, but in the logic and handling edge cases.

Initially I was using Claude 3.5 sonnet, then writing unit tests and manually correcting sonnet's code. Sonnet's code mostly worked, except for failing certain complicated combined book updates.

Then I fed the code and the tests into DeepSeek. It turned out pretty bad. At first it tried to make the results of the tests conform to the erroneous results of the code. When I pointed that out, it fixed the immediate logical problem in the code, introducing two more nested problems that we're not there before by corrupting the existing code. After prompted that, it fixed the first error it introduced but left the second one. Then I fixed it myself, uploaded the fix and asked it to summarize what it has done. It started basically gaslighting me, saying that the initial code had the problem that it introduced.

In summary, I lost two days, reverted everything and went back to Sonnet.