import Tkinter as tk
class HighlightLinesInTextDemo(tk.Tk):
    def __init__(self, *args, **kwargs):
        tk.Tk.__init__(self, *args, **kwargs)
        self.text = tk.Text(self)
        self.text.pack(side="top", fill="both", expand=True)
        self.text.tag_configure("current_line", background="gray")
        self.text.bind("<Motion>", self._highlightline)
        
    def _highlightline(self, event=None):
        self.text.tag_remove("current_line", 1.0, "end")
        self.text.tag_add("current_line", "current linestart", "current lineend+1c")

app = HighlightLinesInTextDemo()
app.mainloop()