fix issues with optional dependencies (#204)

* fix issues with optional dependencies

* format document

* Tree: Format and comment

common/optional_dependencies.py

@@ -0,0 +1,52 @@
+"""Construct a model of all optional dependencies"""
+
+import importlib.util
+from pydantic import BaseModel, computed_field
+
+
+# Declare the exported parts of this module
+__all__ = ["dependencies"]
+
+
+class DependenciesModel(BaseModel):
+    """Model of which optional dependencies are installed."""
+
+    torch: bool
+    exllamav2: bool
+    flash_attn: bool
+    outlines: bool
+    infinity_emb: bool
+    sentence_transformers: bool
+
+    @computed_field
+    @property
+    def extras(self) -> bool:
+        return self.outlines and self.infinity_emb and self.sentence_transformers
+
+    @computed_field
+    @property
+    def exl2(self) -> bool:
+        return self.torch and self.exllamav2 and self.flash_attn
+
+
+def is_installed(package_name: str) -> bool:
+    """Utility function to check if a package is installed."""
+
+    spec = importlib.util.find_spec(package_name)
+    return spec is not None
+
+
+def get_installed_deps() -> DependenciesModel:
+    """Check if optional dependencies are installed by looping over the fields."""
+
+    fields = DependenciesModel.model_fields
+
+    installed_deps = {}
+
+    for field_name in fields.keys():
+        installed_deps[field_name] = is_installed(field_name)
+
+    return DependenciesModel(**installed_deps)
+
+
+dependencies = get_installed_deps()