ID   DC_trip
AC   A9999
SY   DC,Foggy_bottom,22201,H_St.
SY   DC,Smithsonian,12345,14th_St.
//
ID   ...
AC   ...
SY   ...
SY   ...
SY   ...

if lines.find('ID'):
   lines[5:]
elif lines.find('SY'):
   lines[5:]

data = []
# Extract the second row from the input file
# and store it in data
with open('input') as in_file:
    csv_reader = csv.reader(in_file, delimiter='t')
    for row in csv_reader:
       data.append(row[1])

# The first two values in data is the suffix
# for the rest of your output file
suffix = ','.join(data[:2])

# Append the suffix to the rest of the values
# and write it out to the output file.
with open('output') as op_file:
    for item in data[2:]:
        op_file.write('{},{}n'.format(suffix, item))

data = []
with open('file1') as in_file:
    for line in in_file:
        data.append(line.strip().split())
data = [a[1] for a in data if a[1]]