Is there a difference between : “file.readlines()”, “list(file)” and “file.read().splitlines(True)”?

Question

What is the difference between :

with open(\"file.txt\", \"r\") as f:
    data = list(f)

Or :

with open(\"file.txt\", \"r\") as         


        

Answer 1

All three of your options produce the same end result, but nonetheless, one of them is definitely worse than the other two: doing f.read().splitlines(True).

The reason this is the worst option is that it requires the most memory. f.read() reads the file content into memory as a single (maybe huge) string object, then calling .splitlines(True) on that additionally creates the list of the individual lines, and then only after that does the string object containing the file's entire content get garbage collected and its memory freed. So, at the moment of peak memory use - just before the memory for the big string is freed - this approach requires enough memory to store the entire content of the file in memory twice - once as a string, and once as an array of strings.

By contrast, doing list(f) or f.readlines() will read a line from disk, add it to the result list, then read the next line, and so on. So the whole file content is never duplicated in memory, and the peak memory use will thus be about half that of the .splitlines(True) approach. These approaches are thus superior to using .read() and .splitlines(True).

As for list(f) vs f.readlines(), there's no concrete advantage to either of them over the other; the choice between them is a matter of style and taste.