Question

I have a big files to read and process.

Which is the faster method to read the file through and process it.

with open('file') as file:
  for line in file:
      print line

OR

file = open('file')
lines = f.readlines()
file.close()

for line in lines:
  print line

Answer 1

The former can use buffered reading; the latter requires reading the entire file into memory first before it can start looping.

In general, it’s a better idea to use the former; it’s not going to be any slower than the latter and it’s better on memory usage.