How to get line count cheaply in Python?

Question

I need to get a line count of a large file (hundreds of thousands of lines) in python. What is the most efficient way both memory- and time-wise?At the moment I do: def file_len(fname): with open(fname) as f: for i, l in enumerate(f): pass return i + 1is it possible to do any better?

Answer 1

It might be useful to read a block of data from the file and then count the lines in each block:

def blocks(files, size=65536):

while True:

b = files.read(size)if not b: breakyield b

with open("file", "r",encoding="utf-8",errors='ignore') as f:

print (sum(bl.count("\n") for bl in blocks(f)))