Provides a python function with an associated generator object that rapidly counts line in a specified text file. This method only works in python 3.

linecounter.py

def linecount_generator(reader):
    """Yield a generator object for the purpose of counting lines in a file
    at speed. See
    https://stackoverflow.com/questions/
        845058/how-to-get-line-count-cheaply-in-python/27518377#27518377
    """
    b = reader(1024*1024)
    while b:
        yield b
        b = reader(1024*1024)



def countlinesfast(filepath):
    """Count the lines in a file using the generator function 
    linecount_generator."""

    with open(filepath, 'rb') as countfile:
        bufgen = linecountgen(countfile.raw.read)
        nlines = sum( buf.count(b'\n') for buf in bufgen )

    return nlines