"""
Ex 4.4 from "A primer on..." 
Read a sequence of temperatures in degrees Fahrenheit 
from a file, convert to Celsius and store them in two 
lists, then write both temperatures to a new file. 
"""

#empty lists to be filled later:
F = []
C = []

with open('fahrenheit2.txt') as infile:
    # skip first three lines:
    infile.readline()   
    infile.readline()
    infile.readline()

    #use a for-loop to iterate through remaining lines:
    for line in infile:
        #split each line into words
        words = line.split()
        """
        Variable names F_, C_ are used for individual 
        temperatures, to avoid conflict with the names
        for the entire lists, defined above.
        """
        F_ = float(words[-1])
        C_ = (5 / 9) * (F_ - 32)

        F.append(F_)
        C.append(C_)



"""open a new file for writing, and use zip and a for-loop
to traverse the two lists and write the contents to the file."""
with open('degrees.txt','w') as outfile:
    for F_, C_ in zip(F, C):
        outfile.write(f'{F_:5.1f} {C_:5.1f} \n')


"""
Terminal> python f2c_file_read_write.py 
Terminal> more degrees.txt 
 67.2  19.6 
 66.0  18.9 
 78.9  26.1 
102.1  38.9 
 32.0   0.0 
 87.8  31.0 
"""