I have the following loop in Python 2.7.
pressure = ; cycle_flow = ; gauge_val = 
for element in readout_list:
v1_2_3 = extract_sensor_values(element)
v1_2_3=[extract_sensor_values(element) for element in readout_list if element.endswith('.dat')]
This isn't the sort of task that list-comprehensions were created to address. Each list comprehension in your code should produce exactly 1 list.
One thing you could do is use a list-comprehension to get the
guage_val triples and then use
zip to "transpose" the result...
triples = [extract_sensor_values(element) for element in readout_list if element.endswith('.dat')] pressure, cycle_flow, guage_val = zip(*triples)
A word of caution however -- This will leave you with
tuple for the
guage_val variables (instead of
list as was in your original code).