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#!/usr/bin/env python3
from typing import Any, Sequence
class Trie(object):
"""
This is a Trie class, see: https://en.wikipedia.org/wiki/Trie.
It attempts to follow Pythonic container patterns. See doctests
for examples.
"""
def __init__(self):
self.root = {}
self.end = "~END~"
self.length = 0
def insert(self, item: Sequence[Any]):
"""
Insert an item.
>>> t = Trie()
>>> t.insert('test')
>>> t.__contains__('test')
True
"""
current = self.root
for child in item:
current = current.setdefault(child, {})
current[self.end] = self.end
self.length += 1
def __contains__(self, item: Sequence[Any]) -> bool:
"""
Check whether an item is in the Trie.
>>> t = Trie()
>>> t.insert('test')
>>> t.__contains__('test')
True
>>> t.__contains__('testing')
False
>>> 'test' in t
True
"""
current = self.__traverse__(item)
if current is None:
return False
else:
return self.end in current
def contains_prefix(self, item: Sequence[Any]):
"""
Check whether a prefix is in the Trie. The prefix may or may not
be a full item.
>>> t = Trie()
>>> t.insert('testicle')
>>> t.contains_prefix('test')
True
>>> t.contains_prefix('testicle')
True
>>> t.contains_prefix('tessel')
False
"""
current = self.__traverse__(item)
return current is not None
def __traverse__(self, item: Sequence[Any]):
current = self.root
for child in item:
if child in current:
current = current[child]
else:
return None
return current
def __getitem__(self, item: Sequence[Any]):
"""Given an item, return its Trie node which contains all
of the successor (child) node pointers. If the item is not
a node in the Trie, raise a KeyError.
>>> t = Trie()
>>> t.insert('test')
>>> t.insert('testicle')
>>> t.insert('tessera')
>>> t.insert('tesack')
>>> t['tes']
{'t': {'~END~': '~END~', 'i': {'c': {'l': {'e': {'~END~': '~END~'}}}}}, 's': {'e': {'r': {'a': {'~END~': '~END~'}}}}, 'a': {'c': {'k': {'~END~': '~END~'}}}}
"""
ret = self.__traverse__(item)
if ret is None:
raise KeyError(f"Node '{item}' is not in the trie")
return ret
def delete_recursively(self, node, item: Sequence[Any]) -> bool:
if len(item) == 1:
del node[item]
if len(node) == 0 and node is not self.root:
del node
return True
else:
return False
else:
car = item[0]
cdr = item[1:]
lower = node[car]
if self.delete_recursively(lower, cdr):
return self.delete_recursively(node, car)
return False
def __delitem__(self, item: Sequence[Any]):
"""
Delete an item from the Trie.
>>> t = Trie()
>>> t.insert('test')
>>> t.insert('tess')
>>> t.insert('tessel')
>>> len(t)
3
>>> t.root
{'t': {'e': {'s': {'t': {'~END~': '~END~'}, 's': {'~END~': '~END~', 'e': {'l': {'~END~': '~END~'}}}}}}}
>>> t.__delitem__('test')
>>> len(t)
2
>>> t.root
{'t': {'e': {'s': {'s': {'~END~': '~END~', 'e': {'l': {'~END~': '~END~'}}}}}}}
>>> for x in t:
... print(x)
tess
tessel
>>> t.__delitem__('tessel')
>>> len(t)
1
>>> t.root
{'t': {'e': {'s': {'s': {'~END~': '~END~'}}}}}
>>> for x in t:
... print(x)
tess
>>> t.__delitem__('tess')
>>> len(t)
0
>>> t.root
{}
>>> t.insert('testy')
>>> len(t)
1
"""
if item not in self:
raise KeyError(f"Node '{item}' is not in the trie")
self.delete_recursively(self.root, item)
self.length -= 1
def __len__(self):
"""
Returns a count of the Trie's item population.
>>> t = Trie()
>>> len(t)
0
>>> t.insert('test')
>>> len(t)
1
>>> t.insert('testicle')
>>> len(t)
2
"""
return self.length
def __iter__(self):
self.content_generator = self.generate_recursively(self.root, '')
return self
def generate_recursively(self, node, path: Sequence[Any]):
"""
Generate items in the trie one by one.
>>> t = Trie()
>>> t.insert('test')
>>> t.insert('tickle')
>>> for item in t.generate_recursively(t.root, ''):
... print(item)
test
tickle
"""
for child in node:
if child == self.end:
yield path
else:
yield from self.generate_recursively(node[child], path + child)
def __next__(self):
"""
Iterate through the contents of the trie.
>>> t = Trie()
>>> t.insert('test')
>>> t.insert('tickle')
>>> for item in t:
... print(item)
test
tickle
"""
ret = next(self.content_generator)
if ret is not None:
return ret
raise StopIteration
def successors(self, item: Sequence[Any]):
"""
Return a list of the successors of an item.
>>> t = Trie()
>>> t.insert('what')
>>> t.insert('who')
>>> t.insert('when')
>>> t.successors('wh')
['a', 'o', 'e']
>>> u = Trie()
>>> u.insert(['this', 'is', 'a', 'test'])
>>> u.insert(['this', 'is', 'a', 'robbery'])
>>> u.insert(['this', 'is', 'a', 'walrus'])
>>> u.successors(['this', 'is', 'a'])
['test', 'robbery', 'walrus']
"""
node = self.__traverse__(item)
if node is None:
return None
return [x for x in node if x != self.end]
def repr_recursive(self, node, delimiter):
"""
A friendly string representation of the contents of the Trie.
>>> t = Trie()
>>> t.insert([10, 0, 0, 1])
>>> t.insert([10, 0, 0, 2])
>>> t.insert([10, 10, 10, 1])
>>> t.insert([10, 10, 10, 2])
>>> t.repr_recursive(t.root, '.')
'10.[0.0.[1, 2], 10.10.[1, 2]]'
>>> print(t)
10[00[1, 2], 1010[1, 2]]
"""
child_count = 0
my_rep = ''
for child in node:
if child != self.end:
child_count += 1
child_rep = self.repr_recursive(node[child], delimiter)
if len(child_rep) > 0:
my_rep += str(child) + delimiter + child_rep + ", "
else:
my_rep += str(child) + ", "
if len(my_rep) > 1:
my_rep = my_rep[:-2]
if child_count > 1:
my_rep = f'[{my_rep}]'
return my_rep
def __repr__(self):
"""
A friendly string representation of the contents of the Trie. Under
the covers uses repr_recursive with no delimiter
>>> t = Trie()
>>> t.insert([10, 0, 0, 1])
>>> t.insert([10, 0, 0, 2])
>>> t.insert([10, 10, 10, 1])
>>> t.insert([10, 10, 10, 2])
>>> print(t)
10[00[1, 2], 1010[1, 2]]
"""
return self.repr_recursive(self.root, '')
if __name__ == '__main__':
import doctest
doctest.testmod()
|
