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 + 1

is it possible to do any better?

Answer 1

The fastest and one-liner, a solution which is also an efficient way to count lines and it takes less memory and time is as follows:-

num_lines = sum(1 for line in open('myfile.txt'))