Python--Read data files

The script that reads a data file and stores its contents in an array. First data file row is a description of the fields, then the data is divided into two rows. (Using pure Python)

# Funtion to open and read input file
def extract_data(filename):
	infile = open(filename, 'r') # open input file to read
	infile.readline() #first line does not contain data
	x_values = [] # declare empty arrays to store data
	y_values = []
	for line in infile:
		words = line.split() #split lines into words
		x_value = float(words[0]) # cast first component of words from string to float
		y_value = float(words[1]) # cast second component of words from string to float
		x_values.append(x_value)
		y_values.append(y_value)
	infile.close()
	return x_values, y_values
	
# Test function	
X, Y = extract_data('data_file.dat')
print 'x values: ', X
print 'y values: ', Y