how to delete matplotlib data between ploting

[riklaunim at gmail.com]

I want to make few plots from CSV files. I have the code below - it
works  - the first plot is ok, the second one has the first and the
current data set and so on - I can't delete the plot data between
plots.
##########################################
# -*- coding: utf-8 -*-
from pylab import *
from os import listdir

i = listdir('dane/')

# list folders with CSV files
for di in i:
	# list files in folders
	csv = listdir('dane/' + di + '/')
	for datafile in csv:
		# open each CSV file
		file = open('dane/' + di + '/' + datafile, 'r').readlines()
		x = []
		y = []
		# get the data
		for row in file:
			if row.find(',') != -1:
				r = row.split(',')
				if len(r[0]) > 0 and len(r[1]) > 0:
					x.append(float(r[0]))
					y.append(float(r[1]))
		xlabel('czas')
		ylabel('Moc')
		title(di.replace('.', ' '))
		#plot
		plot(x, y)
		savefig('dane/' + di + '/' + datafile + '.png')
                del x
		del y
		del file