这是lec4代码和分别给出的代码：
# non-mutable; persistent linked lists; also a stack
# immutable collections are much easier to use concurrently
#
# NOTE: There are no assignments to self.tail after its initialization
#
class EmptyListE :
def __str__(self) :
return "Exception: list is empty"
class NotFoundE :
def __str__(self) :
return "Exception: element not found"
class IndexOutOfBoundsE :
def __str__(self) :
return "Exception: index out of bounds"
#---
class List :
"""Non-mutable persistent lists
>>> xs = EmptyList().add(1).add(2).add(3).add(4)
>>> print xs
4, 3, 2, 1, []
>>> ys = xs.append(100)
>>> print ys
4, 3, 2, 1, 100, []
>>> print xs
4, 3, 2, 1, []
"""
def size (self) :
"""O(n).
Returns the number of elements in the current list.
>>> EmptyList().size()
0
>>> EmptyList().add(1).add(2).add(3).size()
3
"""
pass
def isEmpty (self) :
"""O(1).
Returns True or False depending on whether the current list is empty or not.
>>> EmptyList().isEmpty()
True
>>> EmptyList().add(1).add(2).add(3).isEmpty()
False
"""
pass
def search (self, v) :
"""O(n).
Returns True or False depending on whether 'v' occurs in the current list or not.
>>> EmptyList().search(1)
False
>>> EmptyList().add(1).add(2).add(3).search(2)
True
>>> EmptyList().add(1).add(2).add(3).search(100)
False
"""
pass
def elem (self, i) :
"""O(n).
Returns the element at zero-based index 'i' in the current list. If 'i' is out
of bounds, raises an exception.
>>> try :
... EmptyList().elem(0)
... except IndexOutOfBoundsE as e :
... print e
...
Exception: index out of bounds
>>> try :
... EmptyList().add(1).add(2).add(3).elem(10)
... except IndexOutOfBoundsE as e :
... print e
...
Exception: index out of bounds
>>> EmptyList().add(1).add(2).add(3).elem(0)
3
>>> EmptyList().add(1).add(2).add(3).elem(1)
2
>>> EmptyList().add(1).add(2).add(3).elem(2)
1
"""
pass
def index (self, v) :
"""O(n).
Returns the zero-based index of the first occurrence of 'v' in the current
list. If 'v' does not occur in the list, raises NotFoundE exception.
>>> try :
... EmptyList().index(1)
... except NotFoundE :
... print 'Not found'
...
Not found
>>> EmptyList().add(1).add(2).add(3).index(3)
0
>>> EmptyList().add(1).add(2).add(3).index(2)
1
>>> EmptyList().add(1).add(2).add(3).index(1)
2
>>> try :
... EmptyList().add(1).add(2).add(3).index(10)
... except NotFoundE :
... print 'Not found'
...
Not found
"""
pass
def insert(self, i, v) :
"""O(n).
Inserts 'v' at the given zero-based index 'i'. If the index i is too large,
throw IndexOutOfBoundsE exception.
>>> str (EmptyList().insert(0,5))
'5, []'
>>> try :
... EmptyList().insert(100,5)
... except IndexOutOfBoundsE as e :
... print e
...
Exception: index out of bounds
>>> str (EmptyList().add(1).add(2).add(3).insert(0,100))
'100, 3, 2, 1, []'
>>> str (EmptyList().add(1).add(2).add(3).insert(1,100))
'3, 100, 2, 1, []'
>>> str (EmptyList().add(1).add(2).add(3).insert(2,100))
'3, 2, 100, 1, []'
>>> str (EmptyList().add(1).add(2).add(3).insert(3,100))
'3, 2, 1, 100, []'
>>> try :
... str (EmptyList().add(1).add(2).add(3).insert(4,100))
... except IndexOutOfBoundsE as e :
... print e
...
Exception: index out of bounds
"""
pass
def remove(self,v) :
"""O(n).
Remove the first occurrence (if any) of 'v' from the current list.
>>> str(EmptyList().remove(10))
'[]'
>>> str(EmptyList().add(1).add(2).add(3).remove(2))
'3, 1, []'
>>> str(EmptyList().add(2).add(2).add(3).remove(2))
'3, 2, []'
"""
pass
def append(self,v) :
"""O(n).
Inserts 'v' at the end of the current list.
>>> str(EmptyList().append(10))
'10, []'
>>> str(EmptyList().add(1).add(2).add(3).append(10))
'3, 2, 1, 10, []'
>>> xs = EmptyList().add(1).add(2).add(3)
>>> print xs
3, 2, 1, []
>>> print xs.append(10)
3, 2, 1, 10, []
>>> print xs
3, 2, 1, []
"""
pass
def drop(self,i) :
"""Drops the first 'i' elements and returns the remaining list; raises an
exception if the index is too large.
>>> xs = EmptyList().add(1).add(2).add(3).add(4)
>>> print xs.drop(0)
4, 3, 2, 1, []
>>> print xs.drop(1)
3, 2, 1, []
>>> print xs.drop(2)
2, 1, []
>>> print xs.drop(3)
1, []
>>> print xs.drop(4)
[]
>>> try :
... xs.drop(5)
... except IndexOutOfBoundsE as e :
... print e
...
Exception: index out of bounds
"""
pass
def add(self,v) :
"""O(1).
Inserts 'v' at the front of the list.
>>> str(EmptyList().add(1).add(2).add(3))
'3, 2, 1, []'
"""
return Node(v,self)
def __iter__ (self) :
"""Creates an iterator.
>>> it = iter(EmptyList().add(1).add(2).add(3))
>>> it.next()
3
>>> it.next()
2
>>> it.next()
1
>>> try :
... it.next()
... except StopIteration :
... print 'Done'
...
Done
>>> for i in EmptyList().add(1).add(2).add(3) :
... print i
...
3
2
1
>>> [ i * i for i in EmptyList().add(1).add(2).add(3) ]
[9, 4, 1]
"""
return ListIterator(self)
#---
class EmptyList (List) :
def size (self) :
return 0
def isEmpty (self) :
return True
def search (self, v) :
return False
def elem (self, i) :
raise IndexOutOfBoundsE()
def index (self, v) :
raise NotFoundE()
def insert(self, i, v) :
if i == 0 :
return Node(v,self)
else :
raise IndexOutOfBoundsE()
def remove(self,v) :
return self
def append(self,v) :
return Node(v,self)
def drop(self,i) :
if i == 0 :
return self
else :
raise IndexOutOfBoundsE()
def __str__ (self) :
return "[]"
#---
class Node (List) :
def __init__ (self, head, tail) :
self.head = head
self.tail = tail
def size (self) :
return 1 + self.tail.size()
def isEmpty (self) :
return False
def search (self, v) :
return self.head == v or self.tail.search(v)
def elem (self, i) :
if i == 0 :
return self.head
else :
return self.tail.elem(i-1)
def index (self, v) :
if self.head == v :
return 0
else :
return 1 + self.tail.index(v)
def insert(self, i, v) :
if i == 0 :
return Node(v,self)
else :
return Node(self.head,self.tail.insert(i-1,v))
def remove(self,v) :
if self.head == v :
return self.tail
else :
return Node(self.head,self.tail.remove(v))
def append(self,v) :
return Node(self.head,self.tail.append(v))
def drop (self,i) :
if i == 0 :
return self
else :
return self.tail.drop(i-1)
def __str__ (self) :
return "%s, %s" % (self.head, self.tail)
#---
class ListIterator :
def __init__(self,list) :
self.list = list
def next(self) :
if self.list.isEmpty() :
raise StopIteration
else :
v = self.list.head
self.list = self.list.tail
return v
#-----------------------------------------------------------------------------
if __name__ == "__main__" :
import doctest
doctest.testmod()
lec4.py的结尾
from lec4 import *
class MutableList :
"""Mutable lists. We maintain a pointer 'front' to a list and use DELEGATION
for read-only operations. Operations that change the list are implemented by
explicit pointer manipulations that update 'front' or self.tail for the relevant
node in the list.
"""
def __init__ (self) :
self.front = EmptyList()
#- easy delegations
def search (self,v) :
"""Returns True or False depending on whether 'v' occurs in the current list or not.
>>> xs = MutableList()
>>> xs.search(1)
False
>>> xs.add(1)
>>> xs.add(2)
>>> xs.add(3)
>>> xs.add(4)
>>> xs.search(2)
True
>>> xs.search(10)
False
"""
#your code goes here
if self.front.isEmpty(self) :
return False
elif !self.front.isEmpty(self) :
return self.front.search(v)
else :
return True
#end of your code
return self.front.search(v)
def isEmpty (self) :
"""Returns True or False depending on whether the current list is empty or not.
>>> xs = MutableList()
>>> xs.isEmpty()
True
>>> xs.add(1)
>>> xs.isEmpty()
False
"""
#your code goes here
if self.front == None : #looks for no elements
return True
else : #an element exists
return False
#code ends here
pass
我曾经尝试的代码：
if self.front == None : #looks for no elements
return True
else : #an element exists
return False
pass
我看过https://docs.python.org/2/tutorial/classes.html和https://docs.python.org/2/tutorial/datastructures.html并且没有找到关于前面成语的任何内容。我不确定它的确切功能及其作用。如果有人可以解释前面的确切内容及其返回声明是什么，如果它有一个。
当我执行调试器时，它表示它没有返回任何意味着它甚至没有输入if语句。为什么这么说呢？
答案 0 :(得分：0)
我需要做的就是从Node类访问isEmpty（）函数。
感谢您的帮助。