# Background

Python provides a standard interface for open files, so that alternate implementations of file-like object can work seamlessly with many function which rely only on the methods of that standard interface. A number of libraries have implemented a similar concept for file-systems, where file operations can be performed on a logical file-system which may be local, structured data store or some remote service.

This repository is intended to be a place to define a standard interface that such file-systems should adhere to, such that code using them should not have to know the details of the implementation in order to operate on any of a number of backends. With hope, the community can come together to define an interface that is the best for the highest number of users, and having the specification, makes developing other file-system implementations simpler.

## History

We have been involved in building a number of remote-data file-system implementations, principally in the context of the Dask project. In particular, several are listed in docs with links to the specific repositories. With common authorship, there is much that is similar between the implementations, for example posix-like naming of the operations, and this has allowed Dask to be able to interact with the various backends and parse generic URLs in order to select amongst them. However, some extra code was required in each case to adapt the peculiarities of each implementation with the generic usage that Dask demanded. People may find the code which parses URLs and creates file-system instances interesting.

At the same time, the Apache Arrow project was also concerned with a similar problem, particularly a common interface to local and HDFS files, for example the hdfs interface (which actually communicated with HDFS with a choice of driver). These are mostly used internally within Arrow, but Dask was modified in order to be able to use the alternate HDFS interface (which solves some security issues with `hdfs3`). In the process, a conversation was started, and I invite all interested parties to continue the conversation in this location.

There is a good argument that this type of code has no place in Dask, which is concerned with making graphs representing computations, and executing those graphs on a scheduler. Indeed, the file-systems are generally useful, and each has a user-base wider than just those that work via Dask.

## Influences

The following places to consider, when choosing the definitions of how we would like the file-system specification to look:

1. python’s os module and its path namespace; also other file-connected functionality in the standard library

2. posix/bash method naming conventions that linux/unix/osx users are familiar with; or perhaps their Windows variants

3. the existing implementations for the various backends (e.g., gcsfs or Arrow’s hdfs)

4. pyfilesystems, an attempt to do something similar, with a plugin architecture. This conception has several types of local file-system, and a lot of well-thought-out validation code.

## Other similar work

It might have been conceivable to reuse code in `pyfilesystems`, which has an established interface and several implementations of its own. However, it supports none of the critical features for cloud and parallel access, and would not be easy to coerce. Following on the success of `s3fs` and `gcsfs`, and their use within Dask, it seemed best to have an interface as close to those as possible. See a discussion on the topic.

Other newer technologies such as smart_open and `pyarrow`’s newer file-system rewrite also have some parts of the functionality presented here, that might suit some use cases better.

## Structure of the package

The best place to get a feel for the contents of `fsspec` is by looking through the Usage and API Reference sections. In addition, the source code will be interesting for those who wish to subclass and develop new file-system implementations. `fsspec/spec.py` contains the main abstract file-system class to derive from, `AbstractFileSystem`.