解决ReST自定义指令的输出导致内置编写器出现Traceback

在使用ReST时，自定义指令的输出导致内置编写器出现traceback的问题。自定义指令将输入转换为表格，表格的形状与输入的字母块相似，每个字母代表一个图像。接下来的几行将图像与每个字母相关联。指令输出的部分代码如下：

tbody = nodes.tbody()
for line in lines[:3]:
    row = []
    for c in line:
        if c not in ingredients:
            continue
        name, image = ingredients[c]
        row.append(nodes.image(uri=IMAGE_URL.format(image)))
    row_entries = [nodes.entry([n]) for n in row]
    row = nodes.row()
    row.extend(row_entries)
    tbody.append(row)

table = nodes.table()
tgroup = nodes.tgroup()
table.append(tgroup)
tgroup.append(tbody)
return [nodes.literal_block(text='\n'.join(self.content))] + table

这段代码在返回时并不会出现问题，但当编写器尝试输出指令返回的内容时，就会导致traceback。错误信息如下：

Traceback (most recent call last):
  File "./rst2html.py", line 24, in <module>
    publish_cmdline(writer_name='html', description=description)
  File "/usr/lib64/python3.2/site-packages/docutils/core.py", line 352, in publish_cmdline
    config_section=config_section, enable_exit_status=enable_exit_status)
  File "/usr/lib64/python3.2/site-packages/docutils/core.py", line 219, in publish
    output = self.writer.write(self.document, self.destination)
  File "/usr/lib64/python3.2/site-packages/docutils/writers/__init__.py", line 80, in write
    self.translate()
  File "/usr/lib64/python3.2/site-packages/docutils/writers/html4css1/__init__.py", line 173, in translate
    self.document.walkabout(visitor)
  File "/usr/lib64/python3.2/site-packages/docutils/nodes.py", line 174, in walkabout
    if child.walkabout(visitor):
  File "/usr/lib64/python3.2/site-packages/docutils/nodes.py", line 174, in walkabout
    if child.walkabout(visitor):
  File "/usr/lib64/python3.2/site-packages/docutils/nodes.py", line 174, in walkabout
    if child.walkabout(visitor):
  File "/usr/lib64/python3.2/site-packages/docutils/nodes.py", line 174, in walkabout
    if child.walkabout(visitor):
  File "/usr/lib64/python3.2/site-packages/docutils/nodes.py", line 174, in walkabout
    if child.walkabout(visitor):
  File "/usr/lib64/python3.2/site-packages/docutils/nodes.py", line 174, in walkabout
    if child.walkabout(visitor):
  File "/usr/lib64/python3.2/site-packages/docutils/nodes.py", line 166, in walkabout
    visitor.dispatch_visit(self)
  File "/usr/lib64/python3.2/site-packages/docutils/nodes.py", line 1627, in dispatch_visit
    return method(node)
  File "/usr/lib64/python3.2/site-packages/docutils/writers/html4css1/__init__.py", line 792, in visit_entry
    if node.parent.parent.parent.stubs[node.parent.column]:
IndexError: list index out of range

这个错误可能是由于返回的表格元素不符合编写器的要求，导致编写器无法正确输出。

2、解决方案 为了解决这个问题，需要对返回的表格元素进行一些调整。

首先，需要为表格添加colgroup元素和colspec元素。colgroup元素用于定义表格的列组，colspec元素用于定义每一列的宽度。

调整后的代码如下：

tgroup = nodes.tgroup()
table.append(tgroup)

for _ in range(3):
    colspec = nodes.colspec(colwidth=1)
    tgroup.append(colspec)

tbody = nodes.tbody()
for line in lines[:3]:
    row = []
    for c in line:
        if c not in ingredients:
            continue
        name, image = ingredients[c]
        row.append(nodes.image(uri=IMAGE_URL.format(image)))
    row_entries = [nodes.entry([n]) for n in row]
    row = nodes.row()
    row.extend(row_entries)
    tbody.append(row)

tgroup.append(tbody)

return [table]

这样修改后，表格元素就符合了编写器的要求，不会再出现traceback错误。