What's the difference between io.open() and os.open() on Python?

Solution 1:

io.open() is the preferred, higher-level interface to file I/O. It wraps the OS-level file descriptor in an object that you can use to access the file in a Pythonic manner.

os.open() is just a wrapper for the lower-level POSIX syscall. It takes less symbolic (and more POSIX-y) arguments, and returns the file descriptor (a number) that represents the opened file. It does not return a file object; the returned value will not have read() or write() methods.

From the os.open() documentation:

This function is intended for low-level I/O. For normal usage, use the built-in function open(), which returns a “file object” with read() and write() methods (and many more).

Solution 2:

Absolutely everything:

• os.open() takes a filename as a string, the file mode as a bitwise mask of attributes, and an optional argument that describes the file permission bits, and returns a file descriptor as an integer.

• io.open() takes a filename as a string or a file descriptor as an integer, the file mode as a string, and optional arguments that describe the file encoding, buffering used, how encoding errors and newlines are handled, and if the underlying FD is closed when the file is closed, and returns some descendant of io.IOBase.

Solution 3:

os.open is very similar to open() from C in Unix. You're unlikely to want to use it unless you're doing something much more low-level. It gives you an actual file descriptor (as in, a number, not an object).

io.open is your basic Python open() and what you want to use just about all the time.

Solution 4:

To add to the existing answers:

I realised that the open() function I've been using was an alias to io.open()

open() == io.open() in Python 3 only. In Python 2 they are different.

While with open() in Python we can obtain an easy-to-use file object with handy read() and write() methods, on the OS level files are accessed using file descriptors (or file handles in Windows). Thus, os.open() should be used implicitly under the hood. I haven't examined Python source code in this regard, but the documentation for the opener parameter, which was added for open() in Python 3.3, says:

A custom opener can be used by passing a callable as opener. The underlying file descriptor for the file object is then obtained by calling opener with (file, flags). opener must return an open file descriptor (passing os.open as opener results in functionality similar to passing None).

So os.open() is the default opener for open(), and we also have the ability to specify a custom wrapper around it if file flags or mode need to be changed. See the documentation for open() for an example of a custom opener, which opens a file relative to a given directory.