# A pipeline of generator functions 

# write a data file "data.tmp" for testing
filename = 'data.tmp'
try:
    # does the data file exist?
    with open(filename,'r') as file:
        pass        
except:
    # doesn't exist, create it
    import numpy as np
    with open(filename,'w') as file:
        for i in range(20):
            file.write(f"{i:<5} {np.random.random():<8.3f} {np.random.random():<8.3f}\n")
        
with open(filename,'r') as file:
    lines = (line for line in file)
    evenlines = (line for line in lines if int(line.split()[0])%2 == 0)
    ycol  = (float(line.split()[2]) for line in evenlines)    
    print("sum(y;even index)=",sum(ycol))