def create_data_row(rain, night, lighting, visibility, speed, surface, danger, danger_cat):
    data_row = []
    data_row.append(rain)
    data_row.append(night)
    data_row.append(lighting)
    data_row.append(visibility)
    data_row.append(speed)
    data_row.append(surface)
    data_row.append(danger)
    data_row.append(danger_cat)

    return data_row

def write_descriptions_to_file(file):
    file.write("RAIN,")
    file.write("NIGHT,")
    file.write("LIGHTING,")
    file.write("VISIBILITY,")
    file.write("SPEED,")
    file.write("SURFACE,")
    file.write("DANGER,")
    file.write("DANGERCATEG")
    file.write("\n")

def write_data_to_file(data_list, file):
    for item in data_list:
        x = str(item) + ","
        file.write(x)
    file.write("\n")


# Κυρίως Πρόγραμμα

f = open("mydatafile.csv", "w")      # δημιουργεί ένα νέο αρχείο
write_descriptions_to_file(f)           # πρώτη σειρά: οι περιγραφές

for i in range (50000):                     
    ...................................
    ...................................
    # δημιουργεί μια σειρά (λίστα) με όλα τα δεδομένα 
    data = create_data_row(nr, nn, nl, nv, nsp, nsu, danger, cat)
    # γράφει τη σειρά (λίστα) δεδομένων στο αρχείο
    write_data_to_file(data, f)

f.close()                                           # κλείνει το αρχείο