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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 activate():
 """Enter into an environment with support for tab-completion This command drops you into a subshell, similar to the one instead it enables tab-completion for supported shells. See documentation for further information. https://github.com/mottosso/be/wiki/cli """


    parent = lib.parent()

    try:
        cmd = lib.cmd(parent)
    except SystemError as exc:
        lib.echo(exc)
        sys.exit(lib.PROGRAM_ERROR)

    # Store reference to calling shell
    context = lib.context(root=_extern.cwd())
    context["BE_SHELL"] = parent

    if lib.platform() == "unix":
        context["BE_TABCOMPLETION"] = os.path.join(
            os.path.dirname(__file__), "_autocomplete.sh").replace("\\", "/")

    context.pop("BE_ACTIVE", None)

    sys.exit(subprocess.call(cmd, env=context))