Question

This code is copy from http://code.google.com/p/closure-library/source/browse/trunk/closure/bin/build/source.py

The Source class’s __str
__method referred self._path

Is it a special property for self?

Cuz, i couldn’t find the place define this variable at Source Class

import re

_BASE_REGEX_STRING = '^\s*goog\.%s\(\s*[\'"](.+)[\'"]\s*\)'
_PROVIDE_REGEX = re.compile(_BASE_REGEX_STRING % 'provide')
_REQUIRES_REGEX = re.compile(_BASE_REGEX_STRING % 'require')

# This line identifies base.js and should match the line in that file.
_GOOG_BASE_LINE = (
    'var goog = goog || {}; // Identifies this file as the Closure base.')


class Source(object):
  """Scans a JavaScript source for its provided and required namespaces."""

  def __init__(self, source):
    """Initialize a source.

    Args:
      source: str, The JavaScript source.
    """

    self.provides = set()
    self.requires = set()

    self._source = source
    self._ScanSource()

  def __str__(self):
    return 'Source %s' % self._path #!!!!!! what is self_path !!!!

  def GetSource(self):
    """Get the source as a string."""
    return self._source

  def _ScanSource(self):
    """Fill in provides and requires by scanning the source."""

    # TODO: Strip source comments first, as these might be in a comment
    # block.  RegExes can be borrowed from other projects.
    source = self.GetSource()

    source_lines = source.splitlines()
    for line in source_lines:
      match = _PROVIDE_REGEX.match(line)
      if match:
        self.provides.add(match.group(1))
      match = _REQUIRES_REGEX.match(line)
      if match:
        self.requires.add(match.group(1))

    # Closure's base file implicitly provides 'goog'.
    for line in source_lines:
      if line == _GOOG_BASE_LINE:
        if len(self.provides) or len(self.requires):
          raise Exception(
              'Base files should not provide or require namespaces.')
        self.provides.add('goog')


def GetFileContents(path):
  """Get a file's contents as a string.

  Args:
    path: str, Path to file.

  Returns:
    str, Contents of file.

  Raises:
    IOError: An error occurred opening or reading the file.

  """
  fileobj = open(path)
  try:
    return fileobj.read()
  finally:
    fileobj.close()

Answer 1

No, _path is just an attribute that may or me not be set on an object like any other attribute. The leading underscore simply means that the author felt it was an internal detail of the object and didn’t want it regarded as part of the public interface.

In this particular case, unless something is setting the attribute from outside that source file, it looks like it’s simply a mistake. It won’t do any harm unless anyone ever tries to call str() on a Source object and probably nobody ever does.

BTW, you seem to be thinking there is something special about self. The name self isn’t special in any way: it’s a convention to use this name for the first parameter of a method, but it is just a name like any other that refers to the object being processed. So if you could access self._path without causing an error you could access it equally well through any other name for the object.