## s3.list_object_sizes()


List a prefix as `{relative path: size}` from one listing call.


Usage

``` python
s3.list_object_sizes(
    directory,
    *,
    recursive=False,
)
```


One listing replaces one remote open per object, which is what makes checking tens of thousands of objects affordable. Only the size is taken: an ETag is the MD5 for a single-part upload and something else for a multipart one, so keying on it would constrain how every writer uploads.


## Parameters


`directory: str, Path, or UPath`  
Prefix to list. Any fsspec-backed path works, including a local one.

`recursive: bool = ``False`  
Include everything below the prefix, keyed by its path relative to the prefix with `/` separators. The default lists the prefix's direct entries by name.


## Returns


`dict of str to int`  
Relative path to size in bytes. Empty when the prefix does not exist.