[mypyc] Use smaller default buffer for BytesWriter#20574
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This seems to make allocations and/or frees a lot faster, at least
in this microbenchmark (on 3.14 it's over 2x faster with the smaller
buffer):
```
def bench(b: bytes, n: int) -> None:
for x in range(n):
w = BytesWriter()
w.write(b)
w.getvalue()
n = 30 * 1000 * 1000
b = b"foo"
bench(b, n)
```
p-sawicki
approved these changes
Jan 13, 2026
Member
|
Hm, I am curious would it make sense to make the same change in |
Member
|
Oh, nvm, your benchmark is for very small bytes object, I guess typical cache files are usually at least 1-2 KB. So maybe it is not relevant for |
Collaborator
Author
|
Yeah, this only helps with very small bytes objects. |
michaelm-openai
pushed a commit
to michaelm-openai/mypy
that referenced
this pull request
Jan 16, 2026
This seems to make allocations and/or frees a lot faster, at least in
this microbenchmark (on 3.14 it's over 2x faster with the smaller
buffer):
```
def bench(b: bytes, n: int) -> None:
for x in range(n):
w = BytesWriter()
w.write(b)
w.getvalue()
n = 30 * 1000 * 1000
b = b"foo"
bench(b, n)
```
michaelm-openai
pushed a commit
to michaelm-openai/mypy
that referenced
this pull request
Jan 16, 2026
This seems to make allocations and/or frees a lot faster, at least in
this microbenchmark (on 3.14 it's over 2x faster with the smaller
buffer):
```
def bench(b: bytes, n: int) -> None:
for x in range(n):
w = BytesWriter()
w.write(b)
w.getvalue()
n = 30 * 1000 * 1000
b = b"foo"
bench(b, n)
```
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This seems to make allocations and/or frees a lot faster, at least in this microbenchmark (on 3.14 it's over 2x faster with the smaller buffer):