## executable.py -- Utilities for dealing with external executables#import os, stringdef exists(file):  """Is this an executable file?"""  return os.path.isfile(file) and os.access(file, os.X_OK)def find(file, dirs=None):  """Search for an executable in a given list of directories.     If no directories are given, search according to the PATH     environment variable."""  if not dirs:    dirs = string.split(os.environ["PATH"], os.pathsep)  for path in dirs:    if is_executable(os.path.join(path, file)):      return os.path.join(path, file)    elif is_executable(os.path.join(path, "%s.exe" % file)):      return os.path.join(path, "%s.exe" % file)  return Nonedef output(cmd, strip=None):  """Run a command and collect all output"""  try:    # Python 2.x    stdin, stdout = os.popen4(cmd)    assert(not stdin.close())  except AttributeError:    try:      # Python 1.x on Unix      import posix      stdout = posix.popen('%s 2>&1' % cmd)    except ImportError:      # Python 1.x on Windows (no cygwin)      # There's no easy way to collect output from stderr, so we'll      # just collect stdout.      stdout = os.popen(cmd)  output = stdout.read()  assert(not stdout.close())  if strip:    return string.strip(output)  else:    return outputdef run(cmd):  """Run a command"""  exit_code = os.system(cmd)  assert(not exit_code)