A trictionary is a pair of tree k and v. They have identical structure: each node in k has a corresponding node in v. The labels in k are called keys. Each key may be the label for multiple nodes in k, and the values for that key are the labels of all the corresponding nodes in v. A lookup function returns one of the values for a key. Specifically, a lookup function for a node in k is a function that takes v as an argument and returns the label for the corresponding node in v. Implement the generator function lookups, which takes as input a tree k and a key. It yields all lookup functions for nodes in k that have key as their label, the functions could be yielded in any order.其中def tree(label, branches=[]): """Construct a tree with the given label value and a list of branches.""" for branch in branches: assert is_tree(branch), 'branches must be trees' return [label] + list(branches)

Sure, here is one possible implementation of the `lookups` generator function:

def lookups(k, key):
    """Yield lookup functions for nodes in k that have key as their label."""
    if label(k) == key:
        yield lambda v: label(v)
    for b in branches(k):
        yield from lookups(b, key)

This implementation uses recursion to traverse the tree `k` and yield lookup functions for all nodes that have the specified `key` as their label. The `yield` statement is used to create a generator that returns each lookup function as soon as it is generated.

Note that this implementation assumes that the `label` and `branches` functions are defined as follows:

def label(tree):
    """Return the label value of the given tree."""
    return tree[0]

def branches(tree):
    """Return the list of branches of the given tree."""
    return tree[1:]

Also note that this implementation does not handle the case where multiple nodes in `k` have the same label `key`. In that case, it would yield multiple lookup functions that return different values for the same key. If you need to handle that case, you could modify the implementation to return a dictionary or a list of values for each key instead of a single value.