Question

I encounter this question when I want to parse a file with large size using pyparsing. I have already created the pyparsing grammar for the whole file. But I am not sure how to feed the string to the parser line by line by reading this big file. Currently I am using the the method like:

pyparsingGrammer = some pyparsing grammar I created
PyparsingGrammar.parseString(open(filename).read())

Except the memory usage for the big read(), another motivation for me to go for line feeding is to extend my parser to a realtime case where info is feeded to the parser one line followed by another.

Answer 1

You could do :

with open(filename) as f:
     for line in f:
         PyparsingGrammar.parseString(line)

using the keyword with automatically closes the file once you are done, and gives you a handle to work with.

for x in something:
    do_something 

is a standard way of going over iterables (stuff which can be iterated, e.g: list, tuple, dictionary in Python.

I forgot to mention, but I guess you figured it:
when you open a file in Python with with open(filename) as f you are getting a list where each line in the list is an item. That is why you are able to treat f as an iterator.