fixed linter errors and ambigious variable names

tudplot/xmgrace.py

@@ -70,7 +70,7 @@ def get_major_ticks(dim):
     def get_major_dticks(axis):
         ticks = getattr(axis, 'get_{}ticks'.format(dim))()
         scale = getattr(axis, 'get_{}scale'.format(dim))()
-        if scale is 'log':
+        if scale == 'log':
             value = (ticks[1:] / ticks[:-1]).mean()
         else:
             value = (ticks[1:] - ticks[:-1]).mean()
@@ -406,7 +406,7 @@ def export_to_agr(figure, filename, **kwargs):
 
     for i, color in enumerate(ValueAttribute.attr_lists['color']):
         # print(i, color)
-        if color is not 'none':
+        if color != 'none':
             rgba, = cc.to_rgba_array(color)
             rgb_tuple = tuple(int(255 * c) for c in rgba[:3])
             color_name = tudcol_rev.get(tuple(rgba), color)