Increase the usage of augmented assignment statements

[elfring]

:eyes: Some source code analysis tools can help to find opportunities for improving software components. :thought_balloon: I propose to increase the usage of augmented assignment statements accordingly.

diff --git a/geomdl/CPGen.py b/geomdl/CPGen.py
index e63112d..a0b235a 100644
--- a/geomdl/CPGen.py
+++ b/geomdl/CPGen.py
@@ -106,11 +106,11 @@ class Grid(object):
                 # Add the first point
                 row.append([current_x, current_y, self._z_value])
                 # Set the y value for the next row
-                current_y = current_y + spacing_y
+                current_y += spacing_y
             # Update the list to be returned
             self._grid_points.append(row)
             # Set x the value for the next column
-            current_x = current_x + spacing_x
+            current_x += spacing_x

         # Set class variables
         self._size_u = num_u
@@ -194,7 +194,7 @@ class Grid(object):
                     trials = max_trials + 1  # set number of trials to a big value
                     break
                 else:
-                    trials = trials + 1
+                    trials += 1
             if trials == max_trials:
                 raise RuntimeError("Cannot generate %d bumps with a base extent of %d on this grid. "
                                    "You need to generate a grid larger than %dx%d."
diff --git a/geomdl/helpers.py b/geomdl/helpers.py
index 98dfe9d..4408fb0 100644
--- a/geomdl/helpers.py
+++ b/geomdl/helpers.py
@@ -938,7 +938,7 @@ def knot_refinement(degree, knotvector, ctrlpts, **kwargs):
             if abs(alpha) < tol:
                 new_ctrlpts[idx - 1] = deepcopy(new_ctrlpts[idx])
             else:
-                alpha = alpha / (new_kv[k + l] - knotvector[i - degree + l])
+                alpha /= new_kv[k + l] - knotvector[i - degree + l]
                 if isinstance(ctrlpts[0][0], float):
                     new_ctrlpts[idx - 1] = [alpha * p1 + (1.0 - alpha) * p2 for p1, p2 in
                                             zip(new_ctrlpts[idx - 1], new_ctrlpts[idx])]
@@ -947,7 +947,7 @@ def knot_refinement(degree, knotvector, ctrlpts, **kwargs):
                         new_ctrlpts[idx - 1][idx2] = [alpha * p1 + (1.0 - alpha) * p2 for p1, p2 in
                                                       zip(new_ctrlpts[idx - 1][idx2], new_ctrlpts[idx][idx2])]
         new_kv[k] = X[j]
-        k = k - 1
+        k -= 1
         j -= 1

     # Return control points and knot vector after refinement
diff --git a/geomdl/multi.py b/geomdl/multi.py
index a7f98f6..2f04e56 100644
--- a/geomdl/multi.py
+++ b/geomdl/multi.py
@@ -425,7 +425,7 @@ class CurveContainer(AbstractContainer):

             # Fix element name
             if elem.name == "curve":
-                elem.name = elem.name + " " + str(idx)
+                elem.name += " " + str(idx)

             # Color selection
             color = select_color(cpcolor, evalcolor, idx=idx)
@@ -1057,7 +1057,7 @@ class VolumeContainer(AbstractContainer):

             # Fix element name
             if elem.name == "volume":
-                elem.name = elem.name + " " + str(idx)
+                elem.name += " " + str(idx)

             # Color selection
             color = select_color(cpcolor, evalcolor, idx=idx)
@@ -1181,7 +1181,7 @@ def process_elements_surface(elem, mconf, colorval, idx, force_tsl, update_delta

     # Fix element name
     if elem.name == "surface" and idx >= 0:
-        elem.name = elem.name + " " + str(idx)
+        elem.name += " " + str(idx)

     # Color selection
     color = select_color(colorval[0], colorval[1], idx=idx)