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Applies a function or op to a number of partially flattened inputs.


The inputs are flattened up to shallow_tree before being mapped.

Use Case:

Sometimes we wish to apply a function to a partially flattened sequence (for example when the function itself takes sequence inputs). We achieve this by specifying a shallow structure, shallow_tree we wish to flatten up to.

The inputs, can be thought of as having the same structure layout as shallow_tree, but with leaf nodes that are themselves tree structures.

This function therefore will return something with the same base structure as shallow_tree.


shallow_tree = [None, None]
inp_val = [1, 2, 3]
out = map_structure_up_to(shallow_tree, lambda x: 2 * x, inp_val)

# Output is: [2, 4]
ab_tuple = collections.namedtuple("ab_tuple", "a, b")
op_tuple = collections.namedtuple("op_tuple", "add, mul")
inp_val = ab_tuple(a=2, b=3)
inp_ops = ab_tuple(a=op_tuple(add=1, mul=2), b=op_tuple(add=2, mul=3))
out = map_structure_up_to(inp_val, lambda val, ops: (val + ops.add) * ops.mul,
                          inp_val, inp_ops)

# Output is: ab_tuple(a=6, b=15)
data_list = [[2, 4, 6, 8], [[1, 3, 5, 7, 9], [3, 5, 7]]]
name_list = ['evens', ['odds', 'primes']]
out = map_structure_up_to(
    lambda name, sec: "first_{}_{}".format(len(sec), name),
    name_list, data_list)

# Output is: ['first_4_evens', ['first_5_odds', 'first_3_primes']]


  • shallow_tree: a shallow tree, common to all the inputs.
  • func: callable which will be applied to each input individually.
  • *inputs: arbitrarily nested combination of objects that are compatible with shallow_tree. The function func is applied to corresponding partially flattened elements of each input, so the function must support arity of len(inputs).
  • **kwargs: kwargs to feed to func(). Special kwarg check_types is not passed to func, but instead determines whether the types of iterables within the structures have to be same (e.g. map_structure(func, [1], (1,)) raises a TypeError exception). To allow this set this argument to False.


  • TypeError: If shallow_tree is a sequence but input_tree is not.
  • TypeError: If the sequence types of shallow_tree are different from input_tree.
  • ValueError: If the sequence lengths of shallow_tree are different from input_tree.


result of repeatedly applying func, with the same structure layout as shallow_tree.