read huge file using for loop : I have a huge file abc.txt and wanted to read line by line, not all at once. I can do as below:  

    filename="c:\abc.txt"
    with open (filename, "r") as fb:
               for content in fb:
                  # do something ....

I am not understanding here one thing. As  you see "fb" is a file pointer over here. How the "for" loop is processing the pointer directly internally even without using any readline or read function ?

