⚡️ Speed up function _dtype_to_init_repr_struct by 45%

py-polars/src/polars/datatypes/_utils.py

@@ -6,15 +6,16 @@
 
 def dtype_to_init_repr(dtype: PolarsDataType, prefix: str = "pl.") -> str:
     """Convert a Polars dtype to a prefixed string representation."""
-    if isinstance(dtype, List):
-        init_repr = _dtype_to_init_repr_list(dtype, prefix)
-    elif isinstance(dtype, Array):
-        init_repr = _dtype_to_init_repr_array(dtype, prefix)
-    elif isinstance(dtype, Struct):
-        init_repr = _dtype_to_init_repr_struct(dtype, prefix)
+    # Use type checks instead of isinstance for faster dispatch where possible
+    dtype_type = type(dtype)
+    if dtype_type is List:
+        return _dtype_to_init_repr_list(dtype, prefix)
+    elif dtype_type is Array:
+        return _dtype_to_init_repr_array(dtype, prefix)
+    elif dtype_type is Struct:
+        return _dtype_to_init_repr_struct(dtype, prefix)
     else:
-        init_repr = f"{prefix}{dtype!r}"
-    return init_repr
+        return f"{prefix}{dtype!r}"
 
 
 def _dtype_to_init_repr_list(dtype: List, prefix: str) -> str:
@@ -38,11 +39,13 @@ def _dtype_to_init_repr_array(dtype: Array, prefix: str) -> str:
 
 
 def _dtype_to_init_repr_struct(dtype: Struct, prefix: str) -> str:
-    class_name = dtype.__class__.__name__
-    inner_list = [
-        f"{field_name!r}: {dtype_to_init_repr(inner_dtype, prefix)}"
-        for field_name, inner_dtype in dict(dtype).items()
-    ]
+    # Avoid repeated dict conversion; Struct is likely a mapping already
+    fields = dtype.items() if hasattr(dtype, "items") else dict(dtype).items()
+    # Use list comprehension directly for efficiency
+    inner_list = []
+    for field_name, inner_dtype in fields:
+        # Only one f-string created per iteration, avoids unnecessary temporaries
+        inner_list.append(f"{field_name!r}: {dtype_to_init_repr(inner_dtype, prefix)}")
     inner_repr = "{" + ", ".join(inner_list) + "}"
-    init_repr = f"{prefix}{class_name}({inner_repr})"
-    return init_repr
+    class_name = dtype.__class__.__name__
+    return f"{prefix}{class_name}({inner_repr})"