Configuring MNE-Python

This tutorial covers how to configure MNE-Python to suit your local system and your analysis preferences.

We begin by importing the necessary Python modules:

# Authors: The MNE-Python contributors.
# License: BSD-3-Clause
# Copyright the MNE-Python contributors.

import os

import mne

Getting and setting configuration variables

Configuration variables are read and written using the functions mne.get_config() and mne.set_config(). To read a specific configuration variable, pass its name to get_config() as the key parameter (key is the first parameter so you can pass it unnamed if you want):

print(mne.get_config("MNE_USE_CUDA"))
print(type(mne.get_config("MNE_USE_CUDA")))

false
<class 'str'>

Note that the string values read from the JSON file are not parsed in any way, so get_config() returns a string even for true/false config values, rather than a Python boolean. Similarly, set_config() will only set string values (or None values, to unset a variable):

try:
    mne.set_config("MNE_USE_CUDA", True)
except TypeError as err:
    print(err)

value must be an instance of str, path-like, or NoneType, got <class 'bool'> instead.

If you’re unsure whether a config variable has been set, there is a convenient way to check it and provide a fallback in case it doesn’t exist: get_config() has a default parameter.

print(mne.get_config("missing_config_key", default="fallback value"))

fallback value

There are also two convenience modes of get_config(). The first will return a dict containing all config variables (and their values) that have been set on your system; this is done by passing key=None (which is the default, so it can be omitted):

print(mne.get_config())  # same as mne.get_config(key=None)

{'MNE_BROWSE_RAW_SIZE': '8.0,8.0', 'MNE_DATASETS_BRAINSTORM_PATH': '/home/circleci/mne_data', 'MNE_DATASETS_EEGBCI_PATH': '/home/circleci/mne_data', 'MNE_DATASETS_EPILEPSY_ECOG_PATH': '/home/circleci/mne_data', 'MNE_DATASETS_ERP_CORE_PATH': '/home/circleci/mne_data', 'MNE_DATASETS_EYELINK_PATH': '/home/circleci/mne_data', 'MNE_DATASETS_FIELDTRIP_CMC_PATH': '/home/circleci/mne_data', 'MNE_DATASETS_FNIRS_MOTOR_PATH': '/home/circleci/mne_data', 'MNE_DATASETS_HF_SEF_PATH': '/home/circleci/mne_data', 'MNE_DATASETS_KILOWORD_PATH': '/home/circleci/mne_data', 'MNE_DATASETS_LIMO_PATH': '/home/circleci/mne_data', 'MNE_DATASETS_MISC_PATH': '/home/circleci/mne_data', 'MNE_DATASETS_MTRF_PATH': '/home/circleci/mne_data', 'MNE_DATASETS_MULTIMODAL_PATH': '/home/circleci/mne_data', 'MNE_DATASETS_OPM_PATH': '/home/circleci/mne_data', 'MNE_DATASETS_PHANTOM_4DBTI_PATH': '/home/circleci/mne_data', 'MNE_DATASETS_PHANTOM_KERNEL_PATH': '/home/circleci/mne_data', 'MNE_DATASETS_PHANTOM_KIT_PATH': '/home/circleci/mne_data', 'MNE_DATASETS_REFMEG_NOISE_PATH': '/home/circleci/mne_data', 'MNE_DATASETS_SAMPLE_PATH': '/home/circleci/mne_data', 'MNE_DATASETS_SOMATO_PATH': '/home/circleci/mne_data', 'MNE_DATASETS_SPM_FACE_PATH': '/home/circleci/mne_data', 'MNE_DATASETS_SSVEP_PATH': '/home/circleci/mne_data', 'MNE_DATASETS_TESTING_PATH': '/home/circleci/mne_data', 'MNE_DATASETS_UCL_OPM_AUDITORY_PATH': '/home/circleci/mne_data', 'MNE_LOGGING_LEVEL': 'info', 'MNE_USE_CUDA': 'false', 'SUBJECTS_DIR': '/home/circleci/mne_data/MNE-fsaverage-data', 'MNE_BROWSER_THEME': 'light', 'MNE_3D_OPTION_THEME': 'light', 'MNE_BROWSER_OVERVIEW_MODE': 'hidden', 'MNE_BROWSER_PRECOMPUTE': 'false', 'MNE_BROWSER_BACKEND': 'qt'}

The second convenience mode will return a tuple of all the keys that MNE-Python recognizes and uses, regardless of whether they’ve been set on your system. This is done by passing an empty string '' as the key:

print(mne.get_config(key=""))

{'MNE_3D_OPTION_ANTIALIAS': 'bool, whether to use full-screen antialiasing in 3D plots', 'MNE_3D_OPTION_DEPTH_PEELING': 'bool, whether to use depth peeling in 3D plots', 'MNE_3D_OPTION_MULTI_SAMPLES': 'int, number of samples to use for full-screen antialiasing', 'MNE_3D_OPTION_SMOOTH_SHADING': 'bool, whether to use smooth shading in 3D plots', 'MNE_3D_OPTION_THEME': 'str, the color theme (light or dark) to use for 3D plots', 'MNE_BROWSE_RAW_SIZE': 'tuple, width and height of the raw browser window (in inches)', 'MNE_BROWSER_BACKEND': 'str, the backend to use for the MNE Browse Raw window (qt or matplotlib)', 'MNE_BROWSER_OVERVIEW_MODE': 'str, the overview mode to use in the MNE Browse Raw window )(see mne.viz.plot_raw for valid options)', 'MNE_BROWSER_PRECOMPUTE': 'bool, whether to precompute raw data in the MNE Browse Raw window', 'MNE_BROWSER_THEME': 'str, the color theme (light or dark) to use for the browser', 'MNE_BROWSER_USE_OPENGL': 'bool, whether to use OpenGL for rendering in the MNE Browse Raw window', 'MNE_CACHE_DIR': 'str, path to the cache directory for parallel execution', 'MNE_COREG_ADVANCED_RENDERING': 'bool, whether to use advanced OpenGL rendering in mne coreg', 'MNE_COREG_COPY_ANNOT': 'bool, whether to copy the annotation files during warping', 'MNE_COREG_FULLSCREEN': 'bool, whether to use full-screen mode in mne coreg', 'MNE_COREG_GUESS_MRI_SUBJECT': 'bool, whether to guess the MRI subject in mne coreg', 'MNE_COREG_HEAD_HIGH_RES': 'bool, whether to use high-res head surface in mne coreg', 'MNE_COREG_HEAD_OPACITY': 'bool, the head surface opacity to use in mne coreg', 'MNE_COREG_HEAD_INSIDE': 'bool, whether to add an opaque inner scalp head surface to help occlude points behind the head in mne coreg', 'MNE_COREG_INTERACTION': 'str, interaction style in mne coreg (trackball or terrain)', 'MNE_COREG_MARK_INSIDE': 'bool, whether to mark points inside the head surface in mne coreg', 'MNE_COREG_PREPARE_BEM': 'bool, whether to prepare the BEM solution after warping in mne coreg', 'MNE_COREG_ORIENT_TO_SURFACE': 'bool, whether to orient the digitization markers to the head surface in mne coreg', 'MNE_COREG_SCALE_LABELS': 'bool, whether to scale the MRI labels during warping in mne coreg', 'MNE_COREG_SCALE_BY_DISTANCE': 'bool, whether to scale the digitization markers by their distance from the scalp in mne coreg', 'MNE_COREG_SCENE_SCALE': 'float, the scale factor of the 3D scene in mne coreg (default 0.16)', 'MNE_COREG_WINDOW_HEIGHT': 'int, window height for mne coreg', 'MNE_COREG_WINDOW_WIDTH': 'int, window width for mne coreg', 'MNE_COREG_SUBJECTS_DIR': 'str, path to the subjects directory for mne coreg', 'MNE_CUDA_DEVICE': 'int, CUDA device to use for GPU processing', 'MNE_DATA': 'str, default data directory', 'MNE_DATASETS_BRAINSTORM_PATH': 'str, path for brainstorm data', 'MNE_DATASETS_EEGBCI_PATH': 'str, path for EEGBCI data', 'MNE_DATASETS_EPILEPSY_ECOG_PATH': 'str, path for epilepsy_ecog data', 'MNE_DATASETS_HF_SEF_PATH': 'str, path for HF_SEF data', 'MNE_DATASETS_MEGSIM_PATH': 'str, path for MEGSIM data', 'MNE_DATASETS_MISC_PATH': 'str, path for misc data', 'MNE_DATASETS_MTRF_PATH': 'str, path for MTRF data', 'MNE_DATASETS_SAMPLE_PATH': 'str, path for sample data', 'MNE_DATASETS_SOMATO_PATH': 'str, path for somato data', 'MNE_DATASETS_MULTIMODAL_PATH': 'str, path for multimodal data', 'MNE_DATASETS_FNIRS_MOTOR_PATH': 'str, path for fnirs_motor data', 'MNE_DATASETS_OPM_PATH': 'str, path for OPM data', 'MNE_DATASETS_SPM_FACE_DATASETS_TESTS': 'str, path for spm_face data', 'MNE_DATASETS_SPM_FACE_PATH': 'str, path for spm_face data', 'MNE_DATASETS_TESTING_PATH': 'str, path for testing data', 'MNE_DATASETS_VISUAL_92_CATEGORIES_PATH': 'str, path for visual_92_categories data', 'MNE_DATASETS_KILOWORD_PATH': 'str, path for kiloword data', 'MNE_DATASETS_FIELDTRIP_CMC_PATH': 'str, path for fieldtrip_cmc data', 'MNE_DATASETS_PHANTOM_KIT_PATH': 'str, path for phantom_kit data', 'MNE_DATASETS_PHANTOM_4DBTI_PATH': 'str, path for phantom_4dbti data', 'MNE_DATASETS_PHANTOM_KERNEL_PATH': 'str, path for phantom_kernel data', 'MNE_DATASETS_LIMO_PATH': 'str, path for limo data', 'MNE_DATASETS_REFMEG_NOISE_PATH': 'str, path for refmeg_noise data', 'MNE_DATASETS_SSVEP_PATH': 'str, path for ssvep data', 'MNE_DATASETS_ERP_CORE_PATH': 'str, path for erp_core data', 'MNE_FORCE_SERIAL': 'bool, force serial rather than parallel execution', 'MNE_LOGGING_LEVEL': 'str or int, controls the level of verbosity of any function decorated with @verbose. See https://mne.tools/stable/auto_tutorials/intro/50_configure_mne.html#logging', 'MNE_MEMMAP_MIN_SIZE': 'str, threshold on the minimum size of arrays passed to the workers that triggers automated memory mapping, e.g., 1M or 0.5G', 'MNE_REPR_HTML': 'bool, represent some of our objects with rich HTML in a notebook environment', 'MNE_SKIP_NETWORK_TESTS': 'bool, used in a test decorator (@requires_good_network) to skip tests that include large downloads', 'MNE_SKIP_TESTING_DATASET_TESTS': 'bool, used in test decorators (@requires_spm_data, @requires_bstraw_data) to skip tests that require specific datasets', 'MNE_STIM_CHANNEL': 'string, the default channel name for mne.find_events', 'MNE_TQDM': 'str, either "tqdm", "tqdm.auto", or "off". Controls presence/absence of progress bars', 'MNE_USE_CUDA': 'bool, use GPU for filtering/resampling', 'MNE_USE_NUMBA': 'bool, use Numba just-in-time compiler for some of our intensive computations', 'SUBJECTS_DIR': 'path-like, directory of freesurfer MRI files for each subject'}

It is possible to add config variables that are not part of the recognized list, by passing any arbitrary key to set_config(). This will yield a warning, however, which is a nice check in cases where you meant to set a valid key but simply misspelled it:

mne.set_config("MNEE_USE_CUUDAA", "false")

/home/circleci/project/tutorials/intro/50_configure_mne.py:79: RuntimeWarning: Setting non-standard config type: "MNEE_USE_CUUDAA"
  mne.set_config("MNEE_USE_CUUDAA", "false")

Let’s delete that config variable we just created. To unset a config variable, use set_config() with value=None. Since we’re still dealing with an unrecognized key (as far as MNE-Python is concerned) we’ll still get a warning, but the key will be unset:

mne.set_config("MNEE_USE_CUUDAA", None)
assert "MNEE_USE_CUUDAA" not in mne.get_config("")

/home/circleci/project/tutorials/intro/50_configure_mne.py:87: RuntimeWarning: Setting non-standard config type: "MNEE_USE_CUUDAA"
  mne.set_config("MNEE_USE_CUUDAA", None)

Where configurations are stored

MNE-Python stores configuration variables in a JSON file. By default, this file is located in %USERPROFILE%\.mne\mne-python.json on Windows and $HOME/.mne/mne-python.json on Linux or macOS. You can get the full path to the config file with mne.get_config_path().

print(mne.get_config_path())

/home/circleci/.mne/mne-python.json

However it is not a good idea to directly edit files in the .mne directory; use the getting and setting functions described in the previous section.

If for some reason you want to load the configuration from a different location, you can pass the home_dir parameter to get_config_path(), specifying the parent directory of the .mne directory where the configuration file you wish to load is stored.

Using environment variables

For compatibility with MNE-C, MNE-Python also reads and writes environment variables to specify configuration. This is done with the same functions that read and write the JSON configuration, and is controlled with the parameters use_env and set_env. By default, get_config() will check os.environ before checking the MNE-Python JSON file; to check only the JSON file use use_env=False. To demonstrate, here’s an environment variable that is not specific to MNE-Python (and thus is not in the JSON config file):

# make sure it's not in the JSON file (no error means our assertion held):
assert mne.get_config("PATH", use_env=False) is None
# but it *is* in the environment:
print(mne.get_config("PATH"))

/home/circleci/python_env/bin:/home/circleci/.local/bin/:/home/circleci/minimal_cmds/bin:/home/circleci/.go_workspace/bin:/usr/local/go/bin:/opt/google/google-cloud-sdk/bin:/opt/circleci/.rbenv/shims:/opt/circleci/.rbenv/bin:/opt/circleci/.pyenv/shims:/opt/circleci/.pyenv/bin:/usr/local/apache-maven/bin:/home/circleci/.yarn/bin:/home/circleci/.config/yarn/global/node_modules/.bin:/home/circleci/bin:/home/circleci/.go_workspace/bin:/usr/local/go/bin:/opt/google/google-cloud-sdk/bin:/opt/circleci/.rbenv/shims:/opt/circleci/.rbenv/bin:/opt/circleci/.pyenv/shims:/opt/circleci/.pyenv/bin:/usr/local/apache-maven/bin:/home/circleci/.yarn/bin:/home/circleci/.config/yarn/global/node_modules/.bin:/opt/circleci/.nvm/versions/node/v20.12.2/bin:/home/circleci/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/snap/bin:/usr/local/gradle-8.7/bin:/usr/local/gradle-8.7/bin

Also by default, set_config() will set values in both the JSON file and in os.environ; to set a config variable only in the JSON file use set_env=False. Here we’ll use print() statement to confirm that an environment variable is being created and deleted (we could have used the Python assert statement instead, but it doesn’t print any output when it succeeds so it’s a little less obvious):

mne.set_config("foo", "bar", set_env=False)
print("foo" in os.environ.keys())
mne.set_config("foo", "bar")
print("foo" in os.environ.keys())
mne.set_config("foo", None)  # unsetting a key deletes var from environment
print("foo" in os.environ.keys())

/home/circleci/project/tutorials/intro/50_configure_mne.py:138: RuntimeWarning: Setting non-standard config type: "foo"
  mne.set_config("foo", "bar", set_env=False)
False
/home/circleci/project/tutorials/intro/50_configure_mne.py:140: RuntimeWarning: Setting non-standard config type: "foo"
  mne.set_config("foo", "bar")
True
/home/circleci/project/tutorials/intro/50_configure_mne.py:142: RuntimeWarning: Setting non-standard config type: "foo"
  mne.set_config("foo", None)  # unsetting a key deletes var from environment
False

Logging

One important configuration variable is MNE_LOGGING_LEVEL. Throughout the module, messages are generated describing the actions MNE-Python is taking behind-the-scenes. How you set MNE_LOGGING_LEVEL determines how many of those messages you see. The default logging level on a fresh install of MNE-Python is info:

print(mne.get_config("MNE_LOGGING_LEVEL"))

info

The logging levels that can be set as config variables are debug, info, warning, error, and critical. Around 90% of the log messages in MNE-Python are info messages, so for most users the choice is between info (tell me what is happening) and warning (tell me only if something worrisome happens). The debug logging level is intended for MNE-Python developers.

In an earlier section we saw how mne.set_config() is used to change the logging level for the current Python session and all future sessions. To change the logging level only for the current Python session, you can use mne.set_log_level() instead. The set_log_level() function takes the same five string options that are used for the MNE_LOGGING_LEVEL config variable; additionally, it can accept int or bool values that are equivalent to those strings. The equivalencies are given in this table:

String	Integer	Boolean
DEBUG	10
INFO	20	True
WARNING	30	False
ERROR	40
CRITICAL	50

With many MNE-Python functions it is possible to change the logging level temporarily for just that function call, by using the verbose parameter. To illustrate this, we’ll load some sample data with different logging levels set. First, with log level warning:

kit_data_path = os.path.join(
    os.path.abspath(os.path.dirname(mne.__file__)),
    "io",
    "kit",
    "tests",
    "data",
    "test.sqd",
)
raw = mne.io.read_raw_kit(kit_data_path, verbose="warning")

No messages were generated, because none of the messages were of severity “warning” or worse. Next, we’ll load the same file with log level info (the default level):

raw = mne.io.read_raw_kit(kit_data_path, verbose="info")

Extracting SQD Parameters from /home/circleci/project/mne/io/kit/tests/data/test.sqd...
Creating Raw.info structure...
Setting channel info structure...
Creating Info structure...
Ready.

This time, we got a few messages about extracting information from the file, converting that information into the MNE-Python Info format, etc. Finally, if we request debug-level information, we get even more detail – and we do so this time using the mne.use_log_level() context manager, which is another way to accomplish the same thing as passing verbose='debug':

with mne.use_log_level("debug"):
    raw = mne.io.read_raw_kit(kit_data_path)

Extracting SQD Parameters from /home/circleci/project/mne/io/kit/tests/data/test.sqd...
Creating Raw.info structure...
    KIT dir entry 0 @ 16
    KIT dir entry 1 @ 32
    KIT dir entry 2 @ 48
    KIT dir entry 3 @ 64
    KIT dir entry 4 @ 80
    KIT dir entry 5 @ 96
    KIT dir entry 6 @ 112
    KIT dir entry 7 @ 128
    KIT dir entry 8 @ 144
    KIT dir entry 9 @ 160
    KIT dir entry 10 @ 176
    KIT dir entry 11 @ 192
    KIT dir entry 12 @ 208
    KIT dir entry 13 @ 224
    KIT dir entry 14 @ 240
    KIT dir entry 15 @ 256
    KIT dir entry 16 @ 272
    KIT dir entry 17 @ 288
    KIT dir entry 18 @ 304
    KIT dir entry 19 @ 320
    KIT dir entry 20 @ 336
    KIT dir entry 21 @ 352
    KIT dir entry 22 @ 368
    KIT dir entry 23 @ 384
    KIT dir entry 24 @ 400
    KIT dir entry 25 @ 416
    KIT dir entry 26 @ 432
    KIT dir entry 27 @ 448
    KIT dir entry 28 @ 464
    KIT dir entry 29 @ 480
    KIT dir entry 30 @ 496
SQD file basic information:
Meg160 version = V2R004
System ID      = 34
System name    = NYU 160ch System since Jan24 2009
Model name     = EQ1160C
Channel count  = 192
Comment        =
Dewar style    = 2
FLL type       = 10
Trigger type   = 21
A/D board type = 12
ADC range      = +/-5.0[V]
ADC allocate   = 16[bit]
ADC bit        = 12[bit]
Setting channel info structure...
Creating Info structure...
Ready.

We’ve been passing string values to the verbose parameter, but we can see from the table above that verbose=True will give us the info messages and verbose=False will suppress them; this is a useful shorthand to use in scripts, so you don’t have to remember the specific names of the different logging levels. One final note: verbose=None (which is the default for functions that have a verbose parameter) will fall back on whatever logging level was most recently set by mne.set_log_level(), or if that hasn’t been called during the current Python session, it will fall back to the value of mne.get_config('MNE_LOGGING_LEVEL').

Getting information about your system

You can also get information about what mne imports as dependencies from your system. This can be done via the command line with:

$ mne sys_info

Or you can use mne.sys_info() directly, which prints to stdout by default:

mne.sys_info()

Platform             Linux-6.8.0-1008-aws-x86_64-with-glibc2.39
Python               3.12.2 (main, May 22 2024, 17:33:50) [GCC 13.2.0]
Executable           /home/circleci/python_env/bin/python
CPU                  Intel(R) Xeon(R) Platinum 8375C CPU @ 2.90GHz (4 cores)
Memory               15.3 GiB

Core
├☑ mne               1.9.0.dev95+g9832d4b7a (devel, latest release is 1.8.0)
├☑ numpy             2.0.2 (OpenBLAS 0.3.27 with 1 thread)
├☑ scipy             1.14.1
└☑ matplotlib        3.9.2 (backend=agg)

Numerical (optional)
├☑ sklearn           1.5.2
├☑ numba             0.60.0
├☑ nibabel           5.3.2
├☑ nilearn           0.10.4
├☑ dipy              1.10.0.dev0+git20241108.aede76c
├☑ openmeeg          2.5.12
├☑ pandas            2.2.3
├☑ h5io              0.2.4
├☑ h5py              3.12.1
└☐ unavailable       cupy

Visualization (optional)
├☑ pyvista           0.45.dev0 (OpenGL 4.5 (Core Profile) Mesa 24.0.9-0ubuntu0.2 via llvmpipe (LLVM 17.0.6, 256 bits))
├☑ pyvistaqt         0.11.1
├☑ vtk               9.3.1
├☑ qtpy              2.4.2 (PyQt6=6.7.1)
├☑ ipympl            0.9.4
├☑ pyqtgraph         0.13.7
├☑ mne-qt-browser    0.6.3
├☑ ipywidgets        8.1.5
├☑ trame_client      3.4.0
├☑ trame_server      3.2.3
├☑ trame_vtk         2.8.12
└☑ trame_vuetify     2.7.1

Ecosystem (optional)
├☑ mne-bids          0.16.0.dev59+g4bea3c0
├☑ mne-nirs          0.7.1
├☑ mne-features      0.3
├☑ mne-connectivity  0.7.0
├☑ mne-icalabel      0.7.0
├☑ mne-bids-pipeline 1.9.0
├☑ neo               0.13.2
├☑ edfio             0.4.5
├☑ mffpy             0.10.0
├☑ pybv              0.7.5
└☐ unavailable       eeglabio