题目
给一棵树,如果树中出现berry则返回true,否则返回False
例如:
>>> scrat = tree('berry')
>>> berry_finder(scrat)
True
>>> sproul = tree('roots', [tree('branch1', [tree('leaf'), tree('berry')]), tree('branch2')])
>>> berry_finder(sproul)
True
‘’‘
tree函数
def tree(root_label, branches=[]):
for branch in branches:
assert is_tree(branch), 'branches must be trees'
return [root_label] + list(branches)
def label(tree):
return tree[0]
def branches(tree):
return tree[1:]
’‘’
正确代码
if label(t) == 'berry':
return True
for ele in branches(t):
if berry_finder(ele):
return True
return False
错误代码
if label(t) == 'berry':
return True
for ele in branches(t):
return berry_finder(ele) or False
错误代码的运行结果
>>> from lab05 import *
>>> scrat = tree('berry')
>>> berry_finder(scrat)
True
>>> sproul = tree('roots', [tree('branch1', [tree('leaf'), tree('berry')]), tree('branch2')])
>>> berry_finder(sproul)
False
# Error: expected
# True
# but got
# False