<pre><code>
# Your huge list will be input.txt
# Your station list will be input2.txt
In [3]: inp1 = open('input.txt')
In [4]: inp2 = open('input2.txt')
# if you don't want to hold anything in memory then this will be hacky solution, memory consuption is also less
with open('input') as inp1:
for i in inp1:
if any([i.startswith(j) for j in inp2]): print(i)
# Result
25MA MIDAS4 2013.3717 2019.1075 5.7358 2007 1279 1398 -0.010216 0.016478
299C MIDAS4 2003.0308 2007.0856 4.0548 1407 1407 2159 -0.003861 -0.021031
# if you want to do some kind of work on filtered data it is better to store it in memory
In [5]: inp1 = {i.split(' ',1)[0] :i.split(' ',1)[1] for i in inp1}
# The above lines read your huge file and convert into key-value pair dict
# result will be something like this.
In [6]: inp1
Out[6]:
{'1ULM': 'MIDAS4 2003.4497 2019.1075 15.6578 5496 4984 7928 -0.013284 -0.000795\n',
'20NA': 'MIDAS4 2008.2355 2017.4511 9.2156 2793 2793 5010 0.031619 0.059160\n',
'21NA': 'MIDAS4 2008.2355 2017.4648 9.2293 3287 3287 5891 0.031598 0.059243\n',
'25MA': 'MIDAS4 2013.3717 2019.1075 5.7358 2007 1279 1398 -0.010216 0.016478\n',
'299C': 'MIDAS4 2003.0308 2007.0856 4.0548 1407 1407 2159 -0.003861 -0.021031\n',
'2TRY': 'MIDAS4 2012.0465 2013.6564 1.6099 564 437 437 0.018726 0.054083'}
# similarly, we are going to do for the station file but slightly a different data structure
In [22]: inp2 = set([i.strip() for i in inp2])
# inp2 will look like
In [23]: inp2
Out[23]: {'25MA', '299C'}
# so to get your result filter the input list based on the station set.
In [24]: res = {k:v for k,v in inp1.items() if k in inp2}
In [25]: res
Out[25]:
{'25MA': 'MIDAS4 2013.3717 2019.1075 5.7358 2007 1279 1398 -0.010216 0.016478\n',
'299C': 'MIDAS4 2003.0308 2007.0856 4.0548 1407 1407 2159 -0.003861 -0.021031\n'}
# Hope this answer helps you
</code></pre>