I'll just bikeshed a bit and say that I'd rewrite this to use a table and an index into the table, viz.

```python
modes = ((REPLACE, "REPLACE"),
         (BLEND, "BLEND"),
         (ADD, "ADD"),
         # etc.
        )
currentMode = 0

def mousePressed:
    currentMode = (currentMode + 1) % len(modes)

def draw():
    mode, name = modes[currentMode]
    # etc.