### Exercise 5.16
### Plot data from a file
### OCL

import sys
import matplotlib.pyplot as plt

# We find file name on the command line
fname = sys.argv[1]   

# We read data into two lists
temp = []
dens = []

# File reading
infile = open(fname, 'r')
for line in infile:
    words = line.split(); 
    # We assume that a line not starting with a hash
    # symbol and with at least two words contains data
    if len(words) >= 2 and words[0] != '#':
        temp.append(float(words[0]))
        dens.append(float(words[1]))
infile.close()

# Plot density vs. temperature
plt.plot(temp, dens, 'bo')       
plt.show()