in src/agents/models/multi_provider.py [0:0]
def _get_fallback_provider(self, prefix: str | None) -> ModelProvider:
if prefix is None or prefix == "openai":
return self.openai_provider
elif prefix in self._fallback_providers:
return self._fallback_providers[prefix]
else:
self._fallback_providers[prefix] = self._create_fallback_provider(prefix)
return self._fallback_providers[prefix]