Added API for using spool weight/length

spoolson/math.py

@@ -0,0 +1,19 @@
+"""Various math-related functions."""
+
+import math
+
+
+def weight_from_length(*, length: float, radius: 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
+        density (float): Density of filament material in g/cm3
+
+    Returns:
+        float: Weight in g
+    """
+    volume_mm3 = length * math.pi * radius * radius
+    volume_cm3 = volume_mm3 / 1000
+    return density * volume_cm3