Conversion math library update

* Now inputs diameter instead of radius to prevent confusion
* Added length_from_weight

spoolman/database/spool.py

@@ -213,7 +213,7 @@ async def use_length(db: AsyncSession, spool_id: int, length: float) -> models.S
     # Calculate and use weight
     weight = weight_from_length(
         length=length,
-        radius=filament_info[0] / 2,
+        diameter=filament_info[0],
         density=filament_info[1],
     )
     await use_weight_safe(db, spool_id, weight)

spoolman/math.py

@@ -3,17 +3,33 @@
 import math
 
 
-def weight_from_length(*, length: float, radius: float, density: float) -> float:
+def weight_from_length(*, length: float, diameter: float, density: float) -> float:
     """Calculate the weight of a piece of filament.
 
     Args:
         length (float): Filament length in mm
-        radius (float): Filament radius in mm
+        diameter (float): Filament diameter in mm
         density (float): Density of filament material in g/cm3
 
     Returns:
         float: Weight in g
     """
-    volume_mm3 = length * math.pi * radius * radius
+    volume_mm3 = length * math.pi * (diameter / 2) ** 2
     volume_cm3 = volume_mm3 / 1000
     return density * volume_cm3
+
+
+def length_from_weight(*, weight: float, diameter: float, density: float) -> float:
+    """Calculate the length of a piece of filament.
+
+    Args:
+        weight (float): Filament weight in g
+        diameter (float): Filament diameter in mm
+        density (float): Density of filament material in g/cm3
+
+    Returns:
+        float: Length in mm
+    """
+    volume_cm3 = weight / density
+    volume_mm3 = volume_cm3 * 1000
+    return volume_mm3 / (math.pi * (diameter / 2) ** 2)