Saving line after line from a txt file - python-2.7

Question

So I wrote this code:
import csv
data = []
filename = "S:\Doc\Python\Data\Dekomp\Hth.txt"
with open(filename) as f:
lines = f.readlines()
for line in lines:
if line.startswith('%'):
data.append(line.split('+')[0].strip())
if line.endswith('%'):
break
with open('S:\Doc\Python\Data\Dekomp\Test.csv', 'w') as f:
writer = csv.writer(f, delimiter=' ')
for line in data:
writer.writerow(line.split())
And my data looks like this:
Headline starts with "%th=number", while number changes from 2 to 180 (each segment plus 2, so it goes (2,4,6... up to180).
Between those segments I have three columns of data, which I would like to append to a csv file. While using my code I save only headliners so (%th=2, %th=4... %th=180). Do you have any idea how to change my code so it will start reading headline, then append data below to a .txt or .csv file, and then starts loop again when it "sees" another headline and continue the process with saving next segment to another file, and that up to "%th=180"?
UPDATE:
Input:
Expected output:
That the program will append to another file all the data below "%th=number", and then when the following segment appears it will save to another file, and the process will continue till the end of this file.
In other words each segment starts with even number so (2, 4, 6, 8 ... 180) so I should get 90 files, each for every segment.
UPDATE 2:
So I have change my code:
with open("S:\Doc\Python\Data\Dekomp\Hth.txt", 'r') as f:
with open("S:\Doc\Python\Data\Dekomp\Hth2.txt", 'w') as g:
for line in f:
if line.startswith("%"):
g.write(line)
if line.endswith("%"):
break
But right now the problem is that if I put this startswith and endswith python will save only headliner, if I delete them, the obivous thing happens, it saves everything from input file.

Answer 1

data = []
filename = "S:\Doc\Python\Data\Dekomp\Hth.txt"
with open(filename) as f:
lines = f.readlines() # Reading file
def _get_all_starting_index(data): # Calculating index of all lines starting with %
return [data.index(line) for line in data if line.startswith("%")]
indices= _get_all_starting_index(lines)
data_info_to_write_in_file = {} # for storing data to write in each individual file
for i in range(len(indices)): # looping over number of indices
key = lines[indices[i]] # key value for starting of a segment.
end_point = indices[i+1] if len(indices) > i+1 else len(indices) # finding end point.
lines_to_get = lines[indices[i]+1 : end_point] # getting lines in between and storing it in dictionary
data_info_to_write_in_file[key] = lines_to_get
for key in data_info_to_write_in_file.keys(): # writing info in each individual file
filename = "S:\Doc\Python\Data\Dekomp\{}.txt".format(key.strip().split("=")[-1])
with open(filename, 'w') as f:
for line in data_info_to_write_in_file[key]:
f.write(line)
Hope it will help.
Feel free to get any info.