qcodes_loop.data.io

IO managers for QCodes.

IO managers wrap whatever physical storage layer the user wants to use in an interface mimicking the built-in <open> context manager, with some restrictions to minimize the overhead in creating new IO managers.

The main thing these managers need to implement is the open context manager:

• Only the context manager needs to be implemented, not separate open function and close methods.

• open takes the standard parameters:

  • filename: (string)

  • mode: (string) only ‘r’ (read), ‘w’ (write), and ‘a’ (append) are expected to be implemented. As with normal file objects, the only difference between write and append is that write empties the file before adding new data, and append leaves the existing contents in place but starts writing at the end.

  • encoding: If a special output encoding is desired. i.e. ‘utf8

• the file-like object returned should implement a minimal set of operations.

  In read mode:

  • read([size]): read to the end or at most size bytes into a string

  • readline([size]): read until a newline or up to size bytes, into a string

  • iter(): usually return self, but can be any iterator over lines

  • next(): assuming iter() returns self, this yields the next line.

  In write or append mode:

  • write(s): add string s to the end of the file.

  • writelines(seq): add a sequence of strings

IO managers should also implement:

• a join method, ala os.path.join(*args).

• a list method, that returns all objects matching location

• a remove method, ala os.remove(path) except that it will remove directories as well as files, since we’re allowing “locations” to be directories or files.

class qcodes_loop.data.io.DiskIO(base_location)

Simple IO object to wrap disk operations with a custom base location.

Also accepts both forward and backward slashes at any point, and normalizes both to the OS we are currently on.

Parameters:

base_location (str) – a path to the root data folder. Converted to an absolute path immediately, so even if you supply a relative path, later changes to the OS working directory will not affect data paths.

isfile(location)

Check whether this location matches a file.

join(*args)

Context-dependent os.path.join for this io manager.

list(location, maxdepth=1, include_dirs=False)

Return all files that match location.

This is either files whose names match up to an arbitrary extension, or any files within an exactly matching directory name.

Parameters:

• location (str) – the location to match. May contain the usual path wildcards * and ?

• maxdepth (Optional[int]) – maximum levels of directory nesting to recurse into looking for files. Default 1.

• include_dirs (Optional[bool]) – whether to allow directories in the results or just files. Default False.

Returns:

A list of matching files and/or directories, as locations relative to our base_location.

open(filename, mode, encoding=None)

Mimic the interface of the built in open context manager.

Parameters:

• filename (str) – path relative to base_location.

• mode (str) – ‘r’ (read), ‘w’ (write), or ‘a’ (append). Other open modes are not supported because we don’t want to force all IO managers to support others.

Returns:

context manager yielding the open file

remove(filename)

Delete a file or folder and prune the directory tree.

remove_all(location)

Delete all files/directories in the dataset at this location.

Afterward prunes the directory tree.

to_location(path)

Convert a local filesystem path into a location string.

Parameters:

path (str) – a path on the local file system.

Returns:

the location string corresponding to this path.

Return type:

str

to_path(location)

Convert a location string into a path on the local file system.

For DiskIO this just fixes slashes and prepends the base location, doing nothing active with the file. But for other io managers that refer to remote storage, this method may actually fetch the file and put it at a temporary local path.

Parameters:

location (str) – A location string for a complete dataset or a file within it.

Returns:

The path on disk to which this location maps.

Return type:

str