Improve error handling in g2c

lmfdb/genus2_curves/main.py

@@ -539,26 +539,30 @@ def genus2_jump(info):
             errmsg = f"unable to find equation {eqn_str} (interpreted from %s) in the genus 2 curve database"
     elif jump.count('=') == 1:
         lhs_str, rhs_str = jump.split('=')
+        errmsg = "Unable to parse input %s into a polynomial"
         try:
             rhs_poly = coeff_to_poly_multi(rhs_str)
-            main_poly_str = lhs_str + "+" + str(-rhs_poly)
-            main_poly = coeff_to_poly_multi(main_poly_str)
         except Exception:
-            errmsg = "Unable to parse input %s into a polynomial"
-            flash_error(errmsg, main_poly_str)
-            return redirect(url_for(".index"))
-        try:
-            f,h = unpack_hyperelliptic_polys(main_poly)
-        except ValueError as e:
-            flash_error(str(e), main_poly)
-            return redirect(url_for(".index"))
-        new_input = str(f) + "," + str(h)
-        label, eqn_str = genus2_lookup_equation(new_input)
-        if label:
-            return redirect(url_for_curve_label(label), 301)
-        elif label is None:
-            # the input was parsed
-            errmsg = f"unable to find equation {eqn_str} (interpreted from %s) in the genus 2 curve database"
+            jump = rhs_str
+        else:
+            try:
+                main_poly_str = lhs_str + "+" + str(-rhs_poly)
+                main_poly = coeff_to_poly_multi(main_poly_str)
+            except Exception:
+                jump = main_poly_str
+            else:
+                try:
+                    f,h = unpack_hyperelliptic_polys(main_poly)
+                except ValueError as e:
+                    errmsg, jump = str(e), main_poly
+                else:
+                    new_input = str(f) + "," + str(h)
+                    label, eqn_str = genus2_lookup_equation(new_input)
+                    if label:
+                        return redirect(url_for_curve_label(label), 301)
+                    elif label is None:
+                        # the input was parsed
+                        errmsg = f"unable to find equation {eqn_str} (interpreted from %s) in the genus 2 curve database"
     else:
         errmsg = "%s is not valid input. Expected a label, e.g., 169.a.169.1"
         errmsg += ", or a univariate polynomial, e.g., x^5 + 1"