convert.py: metres -> feet + inches (whole in, round-half-up)

convert.py

@@ -0,0 +1,32 @@
+#!/usr/bin/env python3
+"""Convert a length in metres to feet and inches (whole inches, round-half-up)."""
+import sys
+
+IN_PER_M = 1.0 / 0.0254  # 1 in = 0.0254 m exactly
+
+
+def m_to_ft_in(m: float) -> tuple[int, int]:
+    total = int(m * IN_PER_M + 0.5)  # round-half-up on total inches
+    return total // 12, total % 12
+
+
+def main(argv):
+    if len(argv) != 2:
+        sys.stderr.write("usage: convert.py <metres>\n")
+        return 1
+    raw = argv[1].rstrip("mM")
+    try:
+        m = float(raw)
+    except ValueError:
+        sys.stderr.write(f"error: '{argv[1]}' is not a number\n")
+        return 1
+    if m < 0:
+        sys.stderr.write("error: length must be non-negative\n")
+        return 1
+    ft, inch = m_to_ft_in(m)
+    print(f"{ft} ft {inch} in")
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main(sys.argv))