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Paul Gauthier 2023-07-01 14:11:35 -07:00
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@ -8,58 +8,50 @@ code in your local git repos.
You can use aider to ask GPT to add features, write tests or make other changes and
improvements to your code.
Having a reliable way for GPT to edit
local source code files is critical to providing this functionality.
Making code editing more reliable often
involves changing and experimenting with
the "edit format" that aider uses.
The edit format is a key part of the system prompt,
specifying how GPT should format code edits in its replies.
Different edit formats can range in
complexity from something simple like "return an updated copy of the whole file" to
a much more sophisticated format
that uses
[OpenAI's new function calling API](https://openai.com/blog/function-calling-and-other-api-updates)
to specify a series of specific diffs
The ability for GPT to reliably edit local source files is
crucial for this functionality. Enhancing the reliability of code
editing often involves modifying and experimenting with the "edit
format" used by aider. The edit format is a critical component of the
system prompt, dictating how GPT should structure code edits in its
responses. Edit formats can vary in complexity, from a simple "return
an updated copy of the whole file" to a more sophisticated format that
employs [OpenAI's new function calling
API](https://openai.com/blog/function-calling-and-other-api-updates)
to specify a series of specific diffs.
To measure the impact of changes to the edit format,
I created a benchmark based on the
[Exercism python](https://github.com/exercism/python)
coding exercises.
This benchmark measures how well aider & GPT can turn
a natural language coding request into
actual runnable code saved into files that pass unit tests.
This is an end-to-end assessment
of not just how well GPT can write code, but also how well it
can *edit existing code* and
*package up those code changes*
so that aider can save the edits to the
local source files.
To measure the impact of changes to the edit format, I developed a
benchmark based on the [Exercism
python](https://github.com/exercism/python) coding exercises. This
benchmark evaluates how effectively aider and GPT can translate a
natural language coding request into actual runnable code saved into
files that pass unit tests. It's an end-to-end evaluation of not just
GPT's code writing ability, but also its capacity to *edit existing
code* and *package those code changes* so that aider can save the
edits to the local source files.
I ran this code editing benchmark
on almost all the ChatGPT models, using a variety of edit formats.
This produced some interesting results:
The results were quite interesting:
- Asking GPT to return an updated copy of the whole file in a normal markdown fenced code block is by far the most reliable and effective edit format. This is true across all GPT-3.5 and GPT-4 models.
- Using the new function calling API is worse than the above whole file method, for all models. GPT writes worse code and frequently mangles this output format, even though the function calling API was introduced to make structured outputs more reliable. This was a big surprise.
- The GPT-4 models are much better at code editing than the GPT-3.5 models, as expected.
- Asking GPT to return an updated copy of the whole file in a standard markdown fenced code block proved to be the most reliable and effective edit format across all GPT-3.5 and GPT-4 models.
- The new function calling API performed worse than the above whole file method for all models. GPT produced inferior code and frequently mangled this output format, despite the function calling API's introduction to enhance the reliability of structured outputs. This was unexpected.
- As anticipated, the GPT-4 models outperformed the GPT-3.5 models in code editing.
The overall quantitative benchmark results agree with an intuition that I've been
developing about how to prompt GPT for complex tasks like coding.
You want to minimize the "cognitive overhead" of formatting the response, so that
GPT can focus on the task at hand.
As an analogy, you wouldn't expect a good result if you asked a junior developer to
implement a new feature by hand typing the required code
changes as `diff -c` formatted edits.
The quantitative benchmark results align with my developing intuition
about prompting GPT for complex tasks like coding. It's beneficial to
minimize the "cognitive overhead" of formatting the response, allowing
GPT to concentrate on the task at hand. As an analogy, asking a junior
developer to implement a new feature by manually typing the required
code changes as `diff -c` formatted edits wouldn't generate a good result.
Using more complex output formats seems to cause two problems:
Using more complex output formats seems to introduce two issues:
- It makes GPT write worse code. Keeping the output format simple seems to leave GPT with more attention to devote to the actual coding task.
- It makes GPT less likely to adhere to the output format. This makes it harder for tooling like aider to correctly identify and apply the edits GPT is trying to make.
- It makes GPT write worse code. Keeping the output format simple appears to allow GPT to devote more attention to the actual coding task.
- It reduces GPT's adherence to the output format, making it more challenging for tools like aider to accurately identify and apply the edits GPT is attempting to make.
I had hoped that the new function calling API would enable more reliable use of
structured output formats, and expected to switch aider to using it
for both GPT-3.5 and GPT-4.
I expected the new function calling API to make
structured output formats more reliable.
I was planning to adopt it in aider for both GPT-3.4 and GPT-4.
But given these benchmarking results, I won't be adopting the functions api
at this time.
@ -70,12 +62,13 @@ More details on the benchmark, edit formats and results are discussed below.
The benchmark uses
[133 practice exercises from the Exercism python repository](https://github.com/exercism/python/tree/main/exercises/practice).
These exercises were designed for people to learn python and practice
These
exercises were designed to help individuals learn Python and hone
their coding skills.
Each exercise has:
Each exercise includes:
- Some instructions for the exercise, in markdown files.
- Instructions for the exercise, provided in markdown files.
- Stub code for the implementation in a python file, specifying the functions/classes that need to be implemented.
- Unit tests in a seperate python file.
@ -94,12 +87,12 @@ Keep and implement the existing function or class stubs, they will be called fro
Only use standard python libraries, don't suggest installing any packages.
```
Aider updates the implementation file based on GPT's reply and runs the unit tests.
If they all pass, we are done. If some tests fail, aider sends
GPT a second message with the test error output.
It only sends the first 50 lines of test errors, to avoid exhausting the context
window of the smaller models.
Aider also includes this final instruction:
Aider updates the implementation file based on GPT's reply and runs
the unit tests. If all tests pass, the exercise is considered
complete. If some tests fail, Aider sends GPT a second message with
the test error output. It only sends the first 50 lines of test errors
to avoid exceeding the context window of the smaller models. Aider
also includes this final instruction:
```
See the testing errors above.
@ -117,24 +110,26 @@ Many of the exercises have multiple paragraphs of instructions,
and most human coders would likely fail some tests on their
first try.
It's worth noting that GPT never gets to see the source code of the unit tests
during the benchmarking.
Just the error output from failed tests.
Of course, all of this code was probably part of its original training data!
It's worth noting that GPT never gets to see the source code of the
unit tests during the benchmarking. It only sees the error output from
failed tests. Of course, all of this code was probably part of its
original training data!
In summary, passing an exercise means GPT was able to:
- write the required code (possibly after reviewing test error output),
- correctly package up all of this code into the edit format so that aider can process and save it to the implementation file.
- Write the required code (possibly after reviewing test error output),
- Correctly package all of this code into the edit format so that Aider can process and save it to the implementation file.
Conversely, failing an exercise only requires a breakdown in one of those steps.
In practice, GPT fails at different steps in different exercises.
Sometimes it just writes the wrong code.
Other times,
it fails to format the code edits in a way that conforms to the edit format so the code isn't saved properly.
Conversely, failing an exercise only requires a breakdown in one of
those steps. In practice, GPT fails at different steps in different
exercises. Sometimes it simply writes the wrong code. Other times, it
fails to format the code edits in a way that conforms to the edit
format, resulting in the code not being saved correctly.
It's worth keeping in mind that changing the edit format often affects both aspects of GPT's performance.
Complex edit formats often make it write worse code *and* make it less successful at formatting the edits correctly.
It's worth keeping in mind that changing the edit format often affects
both aspects of GPT's performance.
Complex edit formats often lead to poorer code *and* make it less
successful at formatting the edits correctly.
## Edit formats
@ -229,20 +224,17 @@ original/updated style edits to be returned using the function call API.
## GPT-3.5 struggles with complex edit formats
While GPT-3.5 is able to pass some exercises using
edit formats other than the `whole` format,
it really struggles with the rest of the formats.
While GPT-3.5 can pass some exercises using edit formats other than
the `whole` format, it struggles with the rest of the
formats.
### Pathlogical use of `diff`
While GPT-3.5 is sometimes able to
correctly generate the `diff` edit format,
it often uses it in a pathological way.
It places the *entire* original source file in the ORIGINAL block
and the entire updated file in the UPDATED block.
This is strictly worse than just using the `whole` edit format,
since GPT is sending 2 full copies of the file.
While GPT-3.5 can sometimes correctly generate the `diff` edit format,
it often uses it in a pathological manner. It places the *entire*
original source file in the ORIGINAL block and the entire updated file
in the UPDATED block. This is strictly worse than just using the
`whole` edit format, as GPT is sending 2 full copies of the file.
### Hallucinating function calls
@ -263,35 +255,34 @@ with the arguments to the function specified in the `name` field.
Instead, GPT-3.5 frequently just stuffs an entire python
file into that field.
It feels like it might be getting confused by fine tuning that was done
for the ChatGPT code interpreter plugin?
It seems like it might be getting confused by fine-tuning that was
done for the ChatGPT code interpreter plugin?
## Randomness
The benchmark attempts to be deterministic, always sending identical
requests for each exercise on repeated runs.
As part of this effort,
when sending test error output to GPT
when sending test error output to GPT,
it removes the wall-clock timing information that
is normally included by the `unittest` module.
The benchmarking harness also logs sha hashes of
The benchmarking harness also logs SHA hashes of
all the OpenAI API requests and replies.
This makes it possible to
detect randomness or nondeterminism
in the bechmarking process.
It turns out that the OpenAI chat APIs are not deterministic, even at `temperature=0`.
The same identical request will produce multiple distinct responses,
usually on the order of 3-6 different variations. This feels
like OpenAI may be
load balancing their API
across a number of slightly different
instances of the model.
It turns out that the OpenAI chat APIs are not deterministic, even at
`temperature=0`. The same identical request will produce multiple
distinct responses, usually less than 5-10 variations. This suggests
that OpenAI may be load balancing their API across a number of
slightly different instances of the model?
For some exercises, some of these variable responses pass the unit tests while
other variants do not. Results for exercises like this which are
"on the bubble"
other variants do not. Results for exercises like this, which are
"on the bubble",
are therefore a bit random, depending on which variant OpenAI returns.
Given that, it would be ideal to run all 133 exercises many times for each
@ -310,7 +301,7 @@ You'll see one set of error bars in the graph, which show
the range of results from those 10 runs.
The OpenAI API randomness doesn't seem to
cause a large variance in the benchmark results.
cause a large variance in the overall benchmark results.
## Conclusions