Python3: what does it mean to f.read(4096)?

[suttiwit]

Basically, I would like to read a binary file in blocks of 4096 bytes. And I know to myself that using f.read(X) makes a system call which would be slow. And since i can't read the whole file and store it in binary because those files are gigabytes in size: I decide to read in blocks of 4096.

But now, I am stumped: I want to know what it means to f.read(4096).... Does it really call a system call once to get the successive 4096 bytes from the file or does it actually call a system call that gets 1 byte from the file 4096 times?

[GarryRicketson]

Python3: what does it mean to f.read(4096)?
This is one, it might help explain,if not there are lots more:
http://stackoverflow.com/questions/6787 ... nd-save-it

[tomazzi]

Basically, I would like to read a binary file in blocks of 4096 bytes. And I know to myself that using f.read(X) makes a system call which would be slow.

It looks like You have completely no idea of what You're actually want to do...
It seems that You've heard *something* about memory pages, but unfortunately You have completely no idea where the 4Kb buffer size comes from... just a disaster... (it's a false assumption that the memory page is 4096 bytes wide)

You should know (and this is the actual answer) that there's a technique, which was developed far before the UNIX started to exist, called: mmap - which allows to access any kind of data stored in a file just like if they were an array of bytes - or, in more advanced cases - a structure...

Regards

[GarryRicketson]

For those that do not know what "mmap" is :

http://man7.org/linux/man-pages/man2/mmap.2.html
and
https://en.wikipedia.org/wiki/Mmap
Also

Code: Select all

$ man Mmap

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