phi_reader.py

def event_generator(phi_column_number, pT_column_number):
    """
    Lazily generate arrays of phi angles and pT for each event.
    
    Fastest way I can find to read a numerical text file in chunks,
    where the chunks are of non-uniform size and separated by markers in the text file.
    
    """
  
    event = []

    for l in sys.stdin:  # or other file object
        s = l.split()
        if not s or s[0].startswith('#'):  # blank lines and comments separate events
            if event:
                yield np.array(event, dtype=np.float64)
                event.clear()
        else:
            event.append(s[phi_column_number], s[pT_column_number])

    if event:
        yield np.array(event, dtype=np.float64)

# example usage
for event in event_generator():
    phi, pT = event.T
    # ...