Robot Framework-robotframework sshllibrary-name错误：name'；平台系统'；没有定义

使用pip安装robotframework sshlibrary时出现以下异常：

python -m pip install robotframework-sshlibrary

Exception:
Traceback (most recent call last):
  File "C:\Program Files (x86)\Python27\lib\site-packages\pip\basecommand.py", line 209, in main
    status = self.run(options, args)
  File "C:\Program Files (x86)\Python27\lib\site-packages\pip\commands\install.py", line 310, in run
    wb.build(autobuilding=True)
  File "C:\Program Files (x86)\Python27\lib\site-packages\pip\wheel.py", line 748, in build
    self.requirement_set.prepare_files(self.finder)
  File "C:\Program Files (x86)\Python27\lib\site-packages\pip\req\req_set.py", line 360, in prepare_files
    ignore_dependencies=self.ignore_dependencies))
  File "C:\Program Files (x86)\Python27\lib\site-packages\pip\req\req_set.py", line 647, in _prepare_file
    set(req_to_install.extras) - set(dist.extras)
  File "C:\Program Files (x86)\Python27\lib\site-packages\pip\_vendor\pkg_resources\__init__.py", line 2810, in extras
    return [dep for dep in self._dep_map if dep]
  File "C:\Program Files (x86)\Python27\lib\site-packages\pip\_vendor\pkg_resources\__init__.py", line 2853, in _dep_map
    self.__dep_map = self._compute_dependencies()
  File "C:\Program Files (x86)\Python27\lib\site-packages\pip\_vendor\pkg_resources\__init__.py", line 2886, in _compute_dependencies
    common = frozenset(reqs_for_extra(None))
  File "C:\Program Files (x86)\Python27\lib\site-packages\pip\_vendor\pkg_resources\__init__.py", line 2883, in reqs_for_extra
    if req.marker_fn(override={'extra':extra}):
  File "C:\Program Files (x86)\Python27\lib\site-packages\pip\_vendor\_markerlib\markers.py", line 113, in marker_fn
    return eval(compiled_marker, environment)
  File "<environment marker>", line 1, in <module>
NameError: name 'platform_system' is not defined

以前，它与其他库配合得很好

例外情况：

python -m pip install robotframework-sshlibrary

Exception:
Traceback (most recent call last):
  File "C:\Program Files (x86)\Python27\lib\site-packages\pip\basecommand.py", line 209, in main
    status = self.run(options, args)
  File "C:\Program Files (x86)\Python27\lib\site-packages\pip\commands\install.py", line 310, in run
    wb.build(autobuilding=True)
  File "C:\Program Files (x86)\Python27\lib\site-packages\pip\wheel.py", line 748, in build
    self.requirement_set.prepare_files(self.finder)
  File "C:\Program Files (x86)\Python27\lib\site-packages\pip\req\req_set.py", line 360, in prepare_files
    ignore_dependencies=self.ignore_dependencies))
  File "C:\Program Files (x86)\Python27\lib\site-packages\pip\req\req_set.py", line 647, in _prepare_file
    set(req_to_install.extras) - set(dist.extras)
  File "C:\Program Files (x86)\Python27\lib\site-packages\pip\_vendor\pkg_resources\__init__.py", line 2810, in extras
    return [dep for dep in self._dep_map if dep]
  File "C:\Program Files (x86)\Python27\lib\site-packages\pip\_vendor\pkg_resources\__init__.py", line 2853, in _dep_map
    self.__dep_map = self._compute_dependencies()
  File "C:\Program Files (x86)\Python27\lib\site-packages\pip\_vendor\pkg_resources\__init__.py", line 2886, in _compute_dependencies
    common = frozenset(reqs_for_extra(None))
  File "C:\Program Files (x86)\Python27\lib\site-packages\pip\_vendor\pkg_resources\__init__.py", line 2883, in reqs_for_extra
    if req.marker_fn(override={'extra':extra}):
  File "C:\Program Files (x86)\Python27\lib\site-packages\pip\_vendor\_markerlib\markers.py", line 113, in marker_fn
    return eval(compiled_marker, environment)
  File "<environment marker>", line 1, in <module>
NameError: name 'platform_system' is not defined

异常：
回溯（最近一次呼叫最后一次）：
文件“C:\Program Files（x86）\Python27\lib\site packages\pip\basecommand.py”，第209行，在main中
status=self.run（选项、参数）
文件“C:\Program Files（x86）\Python27\lib\site packages\pip\commands\install.py”，第310行，正在运行
wb.build（autobuilding=True）
文件“C:\ProgramFiles（x86）\Python27\lib\site packages\pip\wheel.py”，第748行，内部版本
self.requirement\u set.prepare\u文件（self.finder）
文件“C:\Program Files（x86）\Python27\lib\site packages\pip\req\req\u set.py”，第360行，在prepare\u Files中
忽略依赖项=自身。忽略依赖项）
文件“C:\Program Files（x86）\Python27\lib\site packages\pip\req\req\u set.py”，第647行，在\u prepare\u文件中
设置（请求至安装附加）-设置（距离附加）
文件“C:\Program Files（x86）\Python27\lib\site packages\pip\\供应商\pkg\u资源\\uuuuu init\uuuuu.py”，第2810行，附加部分
返回[dep for dep in self.\u dep\u map if dep]
文件“C:\Program Files（x86）\Python27\lib\site packages\pip\\供应商\pkg\u资源\\uu初始\ uuuuuuuuuuuu.py”，第2853行，在dep\u映射中
self.\u dep\u map=self.\u计算依赖项（）
文件“C:\Program Files（x86）\Python27\lib\site packages\pip\\供应商\pkg\u资源\\uu初始\ uuuuuuuuuuuuuuu.py”，第2886行，位于计算依赖项中
通用=冻结集（额外（无）需要）
文件“C:\Program Files（x86）\Python27\lib\site packages\pip\\供应商\pkg\u资源\\uuuuu init\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu
如果请求标记_fn（覆盖={'extra'：extra}）：
文件“C:\Program Files（x86）\Python27\lib\site packages\pip\\u vendor\\u markerlib\markers.py”，第113行，在marker\u fn中
返回值（编译的标记，环境）
文件“”，第1行，在
名称错误：未定义名称“平台\系统”

步骤：

升级了pip（20.0.2）和setuptools（44.0.0）

然后安装robotframework sshlibrary

这是成功的