Importing Brian

After installation, Brian is available in the brian2 package. By doing a wildcard import from this package, i.e.:

from brian2 import *

you will not only get access to the brian2 classes and functions, but also to everything in the pylab package, which includes the plotting functions from matplotlib and everything included in numpy/scipy (e.g. functions such as arange, linspace, etc.). Apart from this when you use the wildcard import, the builtin input function is overshadowed by the input module in the brian2 package. If you wish to use the builtin input function in your program after importing the brian2 package then you can explicitly import the input function again as shown below:

from brian2 import *
from builtins import input

The following topics are not essential for beginners.

Precise control over importing

If you want to use a wildcard import from Brian, but don’t want to import all the additional symbols provided by pylab or don’t want to overshadow the builtin input function, you can use:

from brian2.only import *

Note that whenever you use something different from the most general from brian2 import * statement, you should be aware that Brian overwrites some numpy functions with their unit-aware equivalents (see Units). If you combine multiple wildcard imports, the Brian import should therefore be the last import. Similarly, you should not import and call overwritten numpy functions directly, e.g. by using import numpy as np followed by np.sin since this will not use the unit-aware versions. To make this easier, Brian provides a brian2.numpy_ package that provides access to everything in numpy but overwrites certain functions. If you prefer to use prefixed names, the recommended way of doing the imports is therefore:

import brian2.numpy_ as np
import brian2.only as br2

Note that it is safe to use e.g. np.sin and numpy.sin after a from brian2 import *.

Dependency checks

Brian2 relies on several Python packages (NumPy, SymPy, Jinja2, etc.) to function correctly. Modern Python package managers like pip and conda automatically ensure that compatible versions of these dependencies are installed when you install Brian2.

Recommended installation approach:

The safest way to ensure you have compatible dependencies is to install Brian2 using a package manager:

pip install brian2

or:

conda install -c conda-forge brian2

These commands will automatically install or upgrade dependencies to compatible versions.

If you encounter import errors:

If you see errors when importing Brian2, they typically indicate missing or incompatible dependencies. The error messages will usually tell you which package needs to be installed or updated. For example:

pip install --upgrade numpy

Legacy configurations:

Older versions of Brian2 included runtime dependency version checking controlled by the core.outdated_dependency_error preference. This feature has been removed in favor of relying on package managers for dependency resolution.