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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _startup(self):
 """Private method. Set up logstream, and set the environment variables necessary for a piped build """

        global _ac_config_logs
        global sconf_global
        global SConfFS

        self.lastEnvFs = self.env.fs
        self.env.fs = SConfFS
        self._createDir(self.confdir)
        self.confdir.up().add_ignore( [self.confdir] )

        if self.logfile is not None and not dryrun:
            # truncate logfile, if SConf.Configure is called for the first time
            # in a build
            if self.logfile in _ac_config_logs:
                log_mode = "a"
            else:
                _ac_config_logs[self.logfile] = None
                log_mode = "w"
            fp = open(str(self.logfile), log_mode)
            self.logstream = SCons.Util.Unbuffered(fp)
            # logfile may stay in a build directory, so we tell
            # the build system not to override it with a eventually
            # existing file with the same name in the source directory
            self.logfile.dir.add_ignore( [self.logfile] )

            tb = traceback.extract_stack()[-3-self.depth]
            old_fs_dir = SConfFS.getcwd()
            SConfFS.chdir(SConfFS.Top, change_os_dir=0)
            self.logstream.write('file %s,line %d:\n\tConfigure(confdir = %s)\n' %
                                 (tb[0], tb[1], str(self.confdir)) )
            SConfFS.chdir(old_fs_dir)
        else:
            self.logstream = None
        # we use a special builder to create source files from TEXT
        action = SCons.Action.Action(_createSource,
                                     _stringSource)
        sconfSrcBld = SCons.Builder.Builder(action=action)
        self.env.Append( BUILDERS={'SConfSourceBuilder':sconfSrcBld} )
        self.config_h_text = _ac_config_hs.get(self.config_h, "")
        self.active = 1
        # only one SConf instance should be active at a time ...
        sconf_global = self