Read file in Python

Question

I am new to Python and trying to learn the language structure.

I understand how for statement and open function work. But cannot explain how this piece of code works, which dumps the content of file sample_log.txt to screen:

for line in open("sample_log.txt"):
    print line

These are my questions:

Does open return a list?
When the file actually gets read to memory?
Does the file gets read line by line or all at once?

You should consider reading the documentation on File Objects and the open() function! — jathanism
– jathanism, Commented Dec 9, 2011 at 22:51

tlehman · Accepted Answer · 2011-12-09 22:49:47Z

4

The open function returns a file object, they are iterable, so you can loop over it using a for expression.

answered Dec 9, 2011 at 22:49

tlehman

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3 Comments

Kamyar Souri Over a year ago

Now I get it. So when the file get read and is it line by line or all at once?

John La Rooy Over a year ago

@kamyar, line by line. This is good because it means you can easily process really big files without needing to load them into memory at once

Jeremy D Over a year ago

@KamyarSouri you could also read the entire file in one time : docs.python.org/tutorial/…

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