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-- 61.182.251.99 [DateTime(2004-09-23T16:58:36Z)] TableOfContents

描述

Reading Lines with Continuation Characters 读取含有行连接字符的文件行

问题 Problem

You have a file that includes long logical lines split over two or more physical lines, with backslashes to indicate that a continuation line follows. You want to process a sequence of logical lines, rejoining those split lines.

文件含有逻辑上很长的行，分隔在2个或者更多的物理文件行上，行尾使用'\'符号标记下一行仍然是逻辑上的同一行。需要处理逻辑行的序列，将分开的各物理行合并连接起来。

解决 Solution

As usual, a class is the right way to wrap this functionality in Python 2.1: Python 2.1中，正确方法仍是使用封装类：

class LogicalLines:

• def _ _init_ _(self, fileobj):
  • # Ensure that we get a line-reading sequence in the best way possible: import xreadlines try:
    • # Check if the file-like object has an xreadlines method self.seq = fileobj.xreadlines( )

    except AttributeError:

    • # No, so fall back to the xreadlines module's implementation self.seq = xreadlines.xreadlines(fileobj)
    self.phys_num = 0 # current index into self.seq (physical line number) self.logi_num = 0 # current index into self (logical line number)
  def _ _getitem_ _(self, index):
  • if index != self.logi_num:

    • raise TypeError, "Only sequential access supported"

    self.logi_num += 1 result = [] while 1:

    • # Intercept IndexError, since we may have a last line to return try:

      • # Let's see if there's at least one more line in self.seq line = self.seq[self.phys_num]

      except IndexError:

      • # self.seq is finished, so break the loop if we have any # more data to return; else, reraise the exception, because # if we have no further data to return, we're finished too if result: break else: raise
      self.phys_num += 1 if line.endswith('\\\n'):
      • result.append(line[:-2])
      else:
      • result.append(line) break

    return .join(result)

# Here's an example function, showing off usage: def show_logicals(fileob, numlines=5):

• ll = LogicalLines(fileob) for l in ll:

  • print "Log#%d, phys# %d: %s" % (
    • ll.logi_num, ll.phys_num, repr(l))

    if ll.logi_num>numlines: break

if _ _name_ _=='_ _main_ _':

• from cStringIO import StringIO ff = StringIO(

r"""prima \ seconda \ terza quarta \ quinta sesta settima \ ottava """)

• show_logicals( ff )

讨论 Discussion

• logical_line = [] for physical_line in fileobj:
  • if physical_line.ends_with('\\\n'):
    • logical_line.append(physical_line[:-2])
    else:

    • yield .join(logical_line)+physical_line logical_line = []

  if logical_line: yield .join(logical_line)

参考 See Also