jax.tree_util.tree_map(f, tree, *rest, is_leaf=None)[source]#

Maps a multi-input function over pytree args to produce a new pytree.

  • f (Callable[..., Any]) – function that takes 1 + len(rest) arguments, to be applied at the corresponding leaves of the pytrees.

  • tree (Any) – a pytree to be mapped over, with each leaf providing the first positional argument to f.

  • rest (Any) – a tuple of pytrees, each of which has the same structure as tree or has tree as a prefix.

  • is_leaf (Optional[Callable[[Any], bool]]) – an optionally specified function that will be called at each flattening step. It should return a boolean, which indicates whether the flattening should traverse the current object, or if it should be stopped immediately, with the whole subtree being treated as a leaf.

Return type



A new pytree with the same structure as tree but with the value at each leaf given by f(x, *xs) where x is the value at the corresponding leaf in tree and xs is the tuple of values at corresponding nodes in rest.


>>> import jax.tree_util
>>> jax.tree_util.tree_map(lambda x: x + 1, {"x": 7, "y": 42})
{'x': 8, 'y': 43}

If multiple inputs are passed, the structure of the tree is taken from the first input; subsequent inputs need only have tree as a prefix:

>>> jax.tree_util.tree_map(lambda x, y: [x] + y, [5, 6], [[7, 9], [1, 2]])
[[5, 7, 9], [6, 1, 2]]