Fix 6 Flake8 issues (#6541)

* F541

* F821

* F841

* E741

* E302

* E722

* Apply suggestions from code review

* Update general.py

* Update datasets.py

* Update export.py

* Update plots.py

* Update plots.py

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

utils/plots.py

@@ -54,7 +54,7 @@ def check_pil_font(font=FONT, size=10):
     font = font if font.exists() else (CONFIG_DIR / font.name)
     try:
         return ImageFont.truetype(str(font) if font.exists() else font.name, size)
-    except Exception as e:  # download if missing
+    except Exception:  # download if missing
         check_font(font)
         try:
             return ImageFont.truetype(str(font), size)
@@ -340,7 +340,7 @@ def plot_labels(labels, names=(), save_dir=Path('')):
     matplotlib.use('svg')  # faster
     ax = plt.subplots(2, 2, figsize=(8, 8), tight_layout=True)[1].ravel()
     y = ax[0].hist(c, bins=np.linspace(0, nc, nc + 1) - 0.5, rwidth=0.8)
-    # [y[2].patches[i].set_color([x / 255 for x in colors(i)]) for i in range(nc)]  # update colors bug #3195
+    [y[2].patches[i].set_color([x / 255 for x in colors(i)]) for i in range(nc)]  # update colors bug #3195
     ax[0].set_ylabel('instances')
     if 0 < len(names) < 30:
         ax[0].set_xticks(range(len(names)))