Recursively subtract two UsageMetadata objects.
Token counts cannot be negative so the actual operation is max(left - right, 0).
subtract_usage(
left: UsageMetadata | None,
right: UsageMetadata | None,
) -> UsageMetadataExample:
from langchain_core.messages.ai import subtract_usage
left = UsageMetadata(
input_tokens=5,
output_tokens=10,
total_tokens=15,
input_token_details=InputTokenDetails(cache_read=4),
)
right = UsageMetadata(
input_tokens=3,
output_tokens=8,
total_tokens=11,
output_token_details=OutputTokenDetails(reasoning=4),
)
subtract_usage(left, right)results in
UsageMetadata(
input_tokens=2,
output_tokens=2,
total_tokens=4,
input_token_details=InputTokenDetails(cache_read=4),
output_token_details=OutputTokenDetails(reasoning=0),
)Args:
left: The first UsageMetadata object.
right: The second UsageMetadata object.