我修补一个列表,使其看起来像另一个列表:
a = [x for x in "qabxcd"]
b = [x for x in "abycdf"]
c = a[:]
s = SequenceMatcher(None, a, b)
for tag, i1, i2, j1, j2 in s.get_opcodes():
print ("%7s a[%d:%d] (%s) b[%d:%d] (%s)" %
(tag, i1, i2, a[i1:i2], j1, j2, b[j1:j2]))
if tag == "delete":
del c[i1:i2]
elif tag == "replace":
c[i1:i2] = b[j1-1:j2-1]
elif tag == "insert":
c[i1:i2] = b[j1:j2]
print c
print b
print c == b
a == b
但是列表不相等:
delete a[0:1] (['q']) b[0:0] ([])
equal a[1:3] (['a', 'b']) b[0:2] (['a', 'b'])
replace a[3:4] (['x']) b[2:3] (['y'])
equal a[4:6] (['c', 'd']) b[3:5] (['c', 'd'])
insert a[6:6] ([]) b[5:6] (['f'])
['a', 'b', 'x', 'b', 'd', 'f']
['a', 'b', 'y', 'c', 'd', 'f']
False
有什么问题吗?
所有的动作都会改变索引。当我愿意这样做时,我必须计算变化:
a = [x for x in "abyffgh fg99"]
b = [x for x in "999aby99ff9h9"]
c = a[:]
s = SequenceMatcher(None, a, b)
i = 0
for tag, i1, i2, j1, j2 in s.get_opcodes():
print ("%7s a[%d:%d] (%s) b[%d:%d] (%s) c[%d:%d] (%s)" %
(tag, i1, i2, a[i1:i2], j1, j2, b[j1:j2], i1, i2, c[i1 + i:i2 + i]))
if tag == "delete":
del c[i1 + i:i2 + i]
i -= i2 - i1
elif tag == "replace":
c[i1 + i:i2 + i] = b[j1:j2]
i -= i2 - i1 - j2 + j1
elif tag == "insert":
c[i1 + i:i2 + i] = b[j1:j2]
i += j2 - j1
print c
print i
print c
print b
print c == b
a == b
输出:
['9', '9', '9', 'a', 'b', 'y', '9', '9', 'f', 'f', '9', 'h', ' ', 'f', 'g', '9', '9']
5
delete a[7:10] ([' ', 'f', 'g']) b[12:12] ([]) c[7:10] ([' ', 'f', 'g'])
['9', '9', '9', 'a', 'b', 'y', '9', '9', 'f', 'f', '9', 'h', '9', '9']
1
equal a[10:11] (['9']) b[12:13] (['9']) c[10:11] (['h'])
['9', '9', '9', 'a', 'b', 'y', '9', '9', 'f', 'f', '9', 'h', '9', '9']
1
delete a[11:12] (['9']) b[13:13] ([]) c[11:12] (['9'])
['9', '9', '9', 'a', 'b', 'y', '9', '9', 'f', 'f', '9', 'h', '9']
-1
['9', '9', '9', 'a', 'b', 'y', '9', '9', 'f', 'f', '9', 'h', '9']
['9', '9', '9', 'a', 'b', 'y', '9', '9', 'f', 'f', '9', 'h', '9']
True
我想我可以明白为什么:
s.get_opcodes()
返回的5元组在容器的初始状态下是有效的,也就是说,如果你的对象发生变化,它们必须进行调整:这就是删除操作的情况,特别是,它发生了变化索引(这就是为什么 'x'
没有变成 'y'
)。
据我所知,删除操作是唯一更改索引的操作,因此我将用标记替换已删除的项目(我使用“#”)并在最后将其删除:
>>> c = a[:]
>>> for tag, i1, i2, j1, j2 in s.get_opcodes():
print ("%7s a[%d:%d] (%s) b[%d:%d] (%s)" %
(tag, i1, i2, a[i1:i2], j1, j2, b[j1:j2]))
if tag == "delete":
c[i1:i2] = ['#' for i in range(i1, i2)]
elif tag == "replace":
c[i1:i2] = b[j1:j2]
elif tag == "insert":
c[i1:i1] = b[j1:j2]
print c
delete a[0:1] (['q']) b[0:0] ([])
['#', 'a', 'b', 'x', 'c', 'd']
equal a[1:3] (['a', 'b']) b[0:2] (['a', 'b'])
['#', 'a', 'b', 'x', 'c', 'd']
replace a[3:4] (['x']) b[2:3] (['y'])
['#', 'a', 'b', 'y', 'c', 'd']
equal a[4:6] (['c', 'd']) b[3:5] (['c', 'd'])
['#', 'a', 'b', 'y', 'c', 'd']
insert a[6:6] ([]) b[5:6] (['f'])
['#', 'a', 'b', 'y', 'c', 'd', 'f']
>>> c = [i for i in c if i != '#']
>>> c
['a', 'b', 'y', 'c', 'd', 'f']
>>>
OP 的示例可以通过将
c
初始化为空字符串来稍微简化。那么就不需要处理"delete"
的情况了:
a = "qabxcd"
b = "abycdf"
c = "" # <-- initialize to empty string
s = SequenceMatcher(None, a, b)
for tag, i1, i2, j1, j2 in s.get_opcodes():
...
if tag == "equal":
c += a[i1:i2]
elif tag in ["replace", "insert"]:
c += b[j1:j2]
print(c)
print(b)
assert b == c