add different data at the end of different lines in a file - csv

Question

I have a txt file with the following structure:
I also want to add to the end of each long line, the data (after the comma) of the short lines above them, without the description (STN_NO, STN_ID, INST_HT), like this:
Is it possible? Any ideas?
P.S. I am using Python Version 3.3.

Answer 1

Alternatively, you could use a simpler (albeit longer) solution that does not involve regex.
f = open('file.txt')
for line in f:
line = line.replace('\n', '')
if 'STN_NO' in line:
stn_no = line.split(',')[-1]
print(line)
elif 'STN_ID' in line:
stn_id = line.split(',')[-1]
print(line)
elif 'INST_HT' in line:
inst_ht = line.split(',')[-1]
print(line)
else:
print(line[:-1] + ',' + stn_no + ',' + stn_id + ',' + inst_ht)
Note that this puts the semicolon from the INST_HT line back at the end of every long line. If not desired, it can be removed with inst_ht[:-1].

Answer 2

Let's assume this simplified version of the file in your image:
STN_NO, 41943043
STN_ID, KAST
INST_HT, 1.01500;
Line 1
Line 2
Line 3
STN_NO, 41943062
STN_ID, S2
INST_HT, 0.75;
Line 4
Line 5
Line 6
STN_NO, 123456
STN_ID, XXX
INST_HT, 0.99;
Line 7
Line 8
Line 9
You can use a regex to capture the pattern in blocks and combine:
import re
pat=re.compile(r'^STN_NO,\s+([^\n]+)$\s*^STN_ID,\s+([^\n]+)$\s*^INST_HT,\s+([^;]+);\s*(.*?)(?=^STN_NO|\Z)', re.S | re.M)
with open(fn) as f:
txt=f.read()
for mg in pat.finditer(txt):
for line in mg.group(4).splitlines():
print(line+','+','.join([mg.group(1), mg.group(2), mg.group(3)]))
Prints:
Line 1,41943043,KAST,1.01500
Line 2,41943043,KAST,1.01500
Line 3,41943043,KAST,1.01500
Line 4,41943062,S2,0.75
Line 5,41943062,S2,0.75
Line 6,41943062,S2,0.75
Line 7,123456,XXX,0.99
Line 8,123456,XXX,0.99
Line 9,123456,XXX,0.99
If your file is bigger than what will fit in memory, use mmap to virtualize.