1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
|
class SingletonList:
'''
A SingletonList always has a length of one or 0,
appends overwrite the single element, iteration will
return precisely one element. Attempts to get any item
other than 0 will raise an IndexError or return the single
item depending on whether the 'raiseIndexError' flag is
true or false (generally it should be true except if the
for x in SingletonList: construct is known never to be
used, since this construct will create an infinite loop
if we never raise an IndexError).
'''
def __init__(self,base=None,raiseIndexError=1):
self._base = base
self.raiseIndexError = raiseIndexError
def __len__(self):
'''
The length is 0 if no _base, 1 if a base
'''
if hasattr(self, '_base'):
return 1
else:
return 0
def __getitem__(self,ind):
'''
Get the item if ind == 0, else raise an IndexError or return
the item, depending on the raiseIndexError flag
'''
if ind == 0:
try:
return self._base
except AttributeError:
raise IndexError, ind
elif self.raiseIndexError:
raise IndexError, ind
else:
return self._base
def __setitem__(self,ind, item):
'''
The item is to become the base
'''
self._base = item
def __delitem__(self,ind):
'''
Delete the base, regardless of the index used
'''
try:
del(self._base)
except AttributeError:
raise IndexError, ind
def append(self,item):
'''
Replace the base with the item
'''
self._base = item
def index(self,item):
'''
if the item is the base, return the only valid index (0)
'''
try:
if item == self._base:
return 0
except:
pass
raise ValueError, item
def count(self, item):
'''
If the item is the base, we have one, else 0
'''
try:
if item == self._base:
return 1
except:
pass
return 0
insert = __setitem__
def remove(self, item):
'''
if the item is the base, delete the base, else ValueError
'''
try:
if item == self._base:
del(self._base)
return
except:
pass
raise ValueError, item
def reverse(self):
pass
def sort(self):
pass
def __repr__(self):
try:
return '[%s]'%`self._base`
except AttributeError:
return '[]'
# store and copy functions
# def __getinitargs__(self):
# return (self._base,self.raiseIndexError)
# def __getstate__(self,*args,**namedargs):
# pass
# def __setstate__(self,*args,**namedargs):
# pass
|
