Neo IO¶

Preamble¶

The Neo io module aims to provide an exhaustive way of loading and saving several widely used data formats in electrophysiology. The more these heterogeneous formats are supported, the easier it will be to manipulate them as Neo objects in a similar way. Therefore the IO set of classes propose a simple and flexible IO API that fits many format specifications. It is not only file-oriented, it can also read/write objects from a database.

At the moment, there are 3 families of IO modules:

for reading closed manufacturers’ formats (Spike2, Plexon, AlphaOmega, BlackRock, Axon, …)
for reading(/writing) formats from open source tools (KlustaKwik, Elan, WinEdr, WinWcp, …)
for reading/writing Neo structure in neutral formats (HDF5, .mat, …) but with Neo structure inside (NeoHDF5, NeoMatlab, …)

Combining 1 for reading and 3 for writing is a good example of use: converting your datasets to a more standard format when you want to share/collaborate.

Introduction¶

There is an intrinsic structure in the different Neo objects, that could be seen as a hierachy with cross-links. See Neo core. The highest level object is the Block object, which is the high level container able to encapsulate all the others.

A Block has therefore a list of Segment objects, that can, in some file formats, be accessed individually. Depending on the file format, i.e. if it is streamable or not, the whole Block may need to be loaded, but sometimes particular Segment objects can be accessed individually. Within a Segment, the same hierarchical organisation applies. A Segment embeds several objects, such as SpikeTrain, AnalogSignal, IrregularlySampledSignal, Epoch, Event (basically, all the different Neo objects).

Depending on the file format, these objects can sometimes be loaded separately, without the need to load the whole file. If possible, a file IO therefore provides distinct methods allowing to load only particular objects that may be present in the file. The basic idea of each IO file format is to have, as much as possible, read/write methods for the individual encapsulated objects, and otherwise to provide a read/write method that will return the object at the highest level of hierarchy (by default, a Block or a Segment).

The neo.io API is a balance between full flexibility for the user (all read_XXX() methods are enabled) and simple, clean and understandable code for the developer (few read_XXX() methods are enabled). This means that not all IOs offer the full flexibility for partial reading of data files.

One format = one class¶

The basic syntax is as follows. If you want to load a file format that is implemented in a generic MyFormatIO class:

>>> from neo.io import MyFormatIO
>>> reader = MyFormatIO(filename="myfile.dat")

you can replace MyFormatIO by any implemented class, see List of implemented formats

Modes¶

An IO module can be based on a single file, a directory containing files, or a database. This is described in the mode attribute of the IO class.

>>> from neo.io import MyFormatIO
>>> print MyFormatIO.mode
'file'

For file mode the filename keyword argument is necessary. For directory mode the dirname keyword argument is necessary.

Ex:

>>> reader = io.PlexonIO(filename='File_plexon_1.plx')
>>> reader = io.TdtIO(dirname='aep_05')

Supported objects/readable objects¶

To know what types of object are supported by a given IO interface:

>>> MyFormatIO.supported_objects
[Segment , AnalogSignal , SpikeTrain, Event, Spike]

Supported objects does not mean objects that you can read directly. For instance, many formats support AnalogSignal but don’t allow them to be loaded directly, rather to access the AnalogSignal objects, you must read a Segment:

>>> seg = reader.read_segment()
>>> print(seg.analogsignals)
>>> print(seg.analogsignals[0])

To get a list of directly readable objects

>>> MyFormatIO.readable_objects
[Segment]

The first element of the previous list is the highest level for reading the file. This mean that the IO has a read_segment() method:

>>> seg = reader.read_segment()
>>> type(seg)
neo.core.Segment

All IOs have a read() method that returns a list of Block objects (representing the whole content of the file):

>>> bl = reader.read()
>>> print bl[0].segments[0]
neo.core.Segment

Read a time slice of Segment¶

Some objects support the time_slice argument in read_segment(). This is useful to read only a subset of a dataset clipped in time. By default time_slice=None meaning load eveything.

This reads everything:

seg = reader.read_segment(time_slice=None)

This reads only the first 5 seconds:

seg = reader.read_segment(time_slice=(0*pq.s, 5.*pq.s))

Lazy option and proxy objects¶

In some cases you may not want to load everything in memory because it could be too big. For this scenario, some IOs implement lazy=True/False. Since neo 0.7, a new lazy sytem have been added for some IO modules (all IO classes that inherit from rawio). To know if a class supports lazy mode use ClassIO.support_lazy.

With lazy=True all data objects (AnalogSignal/SpikeTrain/Event/Epoch) are replaced by proxy objects (AnalogSignalProxy/SpikeTrainProxy/EventProxy/EpochProxy).

By default (if not specified), lazy=False, i.e. all data is loaded.

These proxy objects contain metadata (name, sampling_rate, id, …) so they can be inspected but they do not contain any array-like data. All proxy objects contain a load() method to postpone the real load of array like data.

Further more the load() method has a time_slice argument to load only a slice from the file. In this way the consumption of memory can be finely controlled.

Here are two examples that read a dataset, extract sections of the signal based on recorded events, and averages the sections.

The first example is without lazy mode, so it consumes more memory:

lim0, lim1 = -500 * pq.ms, +1500 * pq.ms
seg = reader.read_segment(lazy=False)
triggers = seg.events[0]
sig = seg.analogsignals[0]  # here sig contain the whole recording in memory
all_sig_chunks = []
for t in triggers.times:
    t0, t1 = (t + lim0), (t + lim1)
    sig_chunk = sig.time_slice(t0, t1)
    all_sig_chunks.append(sig_chunk)
apply_my_fancy_average(all_sig_chunks)

The second example uses lazy mode, so it consumes less memory:

lim0, lim1 = -500*pq.ms, +1500*pq.ms
seg = reader.read_segment(lazy=True)
triggers = seg.events[0].load(time_slice=None)  # this loads all triggers in memory
sigproxy = seg.analogsignals[0]  # this is a proxy
all_sig_chunks = []
for t in triggers.times:
    t0, t1 = (t + lim0), (t + lim1)
    sig_chunk = sigproxy.load(time_slice=(t0, t1))  # here real data are loaded
    all_sig_chunks.append(sig_chunk)
apply_my_fancy_average(all_sig_chunks)

In addition to time_slice, AnalogSignalProxy supports the channel_indexes argument. This allows loading only a subset of channels. This is useful where the channel count is very high.

In this example, we read only three selected channels:

seg = reader.read_segment(lazy=True)
anasig = seg.analogsignals[0].load(time_slice=None, channel_indexes=[0, 2, 18])

Details of API¶

The neo.io API is designed to be simple and intuitive:

each file format has an IO class (for example for Spike2 files you have a Spike2IO class).
each IO class inherits from the BaseIO class.
each IO class can read or write directly one or several Neo objects (for example Segment, Block, …): see the readable_objects and writable_objects attributes of the IO class.
each IO class supports part of the neo.core hierachy, though not necessarily all of it (see supported_objects).
each IO class has a read() method that returns a list of Block objects. If the IO only supports Segment reading, the list will contain one block with all segments from the file.
each IO class that supports writing has a write() method that takes as a parameter a list of blocks, a single block or a single segment, depending on the IO’s writable_objects.
some IO are able to do a lazy load: all metadata (e.g. sampling_rate) are read, but not the actual numerical data.
each IO is able to save and load all required attributes (metadata) of the objects it supports.
each IO can freely add user-defined or manufacturer-defined metadata to the annotations attribute of an object.

If you want to develop your own IO¶

See IO developers’ guide for information on how to implement a new IO.

List of implemented formats¶

Logging¶

neo uses the standard Python logging module for logging. All neo.io classes have logging set up by default, although not all classes produce log messages. The logger name is the same as the full qualified class name, e.g. neo.io.nixio.NixIO. By default, only log messages that are critically important for users are displayed, so users should not disable log messages unless they are sure they know what they are doing. However, if you wish to disable the messages, you can do so:

>>> import logging
>>>
>>> logger = logging.getLogger('neo')
>>> logger.setLevel(100)

Some io classes provide additional information that might be interesting to advanced users. To enable these messages, do the following:

>>> import logging
>>>
>>> logger = logging.getLogger('neo')
>>> logger.setLevel(logging.INFO)

It is also possible to log to a file in addition to the terminal:

>>> import logging
>>>
>>> logger = logging.getLogger('neo')
>>> handler = logging.FileHandler('filename.log')
>>> logger.addHandler(handler)

To only log to the terminal:

>>> import logging
>>> from neo import logging_handler
>>>
>>> logger = logging.getLogger('neo')
>>> handler = logging.FileHandler('filename.log')
>>> logger.addHandler(handler)
>>>
>>> logging_handler.setLevel(100)

This can also be done for individual IO classes:

>>> import logging
>>>
>>> logger = logging.getLogger('neo.io.nixio.NixIO')
>>> handler = logging.FileHandler('filename.log')
>>> logger.addHandler(handler)

Individual IO classes can have their loggers disabled as well:

>>> import logging
>>>
>>> logger = logging.getLogger('neo.io.nixio.NixIO')
>>> logger.setLevel(100)

And more detailed logging messages can be enabled for individual IO classes:

>>> import logging
>>>
>>> logger = logging.getLogger('neo.io.nixio.NixIO')
>>> logger.setLevel(logging.INFO)

The default handler, which is used to print logs to the command line, is stored in neo.logging_handler. This example changes how the log text is displayed:

>>> import logging
>>> from neo import logging_handler
>>>
>>> formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
>>> logging_handler.setFormatter(formatter)

For more complex logging, please see the documentation for the logging module.

Note

If you wish to implement more advanced logging as describe in the documentation for the logging module or elsewhere on the internet, please do so before calling any neo functions or initializing any neo classes. This is because the default handler is created when neo is imported, but it is not attached to the neo logger until a class that uses logging is initialized or a function that uses logging is called. Further, the handler is only attached if there are no handlers already attached to the root logger or the neo logger, so adding your own logger will override the default one. Additional functions and/or classes may get logging during bugfix releases, so code relying on particular modules not having logging may break at any time without warning.

Table of Contents

Previous topic

Next topic

This Page