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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def heatmap(n_x=5,n_y=10):
 	""" 	Returns a DataFrame with the required format for 	a heatmap plot 	Parameters: 		n_x : int 			Number of x categories 		n_y : int 			Number of y categories 	"""
	
	x=['x_'+str(_) for _ in range(n_x)]
	y=['y_'+str(_) for _ in range(n_y)]
	return pd.DataFrame(surface(n_x-1,n_y-1).values,index=x,columns=y)