What is meant with a buffer in python

Question

In the python documentation for struct, the word buffer is used without explanation:

http://docs.python.org/library/struct.html

struct.unpack_from(fmt, buffer[,offset=0])

Unpack the buffer according to the given format. The result is a tuple even if it contains exactly one item. The buffer must contain at least the amount of data required by the format (len(buffer[offset:]) must be at least calcsize(fmt)).

What is meant here with a buffer. Is a string a buffer, or a file descriptor? What methods must a 'buffer' have?

Fred Foo · Accepted Answer · 2011-03-28 09:11:32Z

4

It's a memory buffer: in Python 2, a string (str), in Python 3, a binary string (bytes), or alternatively an object constructed with buffer.

edited Mar 28, 2011 at 9:11

answered Mar 28, 2011 at 9:05

Fred Foo

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4 Comments

Peter Smit Over a year ago

The buffer function talks about an object that supports the buffer call interface. What is this interface? Does a file descriptor match that, or should I always read into a string first?

Fred Foo Over a year ago

python.org/dev/peps/pep-3118 A file descriptor or file-like object won't work.

Sylvain Defresne Over a year ago

You can use mmap to have a memory map to a file without having to read it into a file. docs.python.org/library/mmap.html

Fred Foo Over a year ago

mmap won't work with remote filesystems, though, so be prepared to write a backup routine that does read in the file.

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