Robot Framework：导入Selenium2LIbrary失败

安装的版本信息：

>pip list
AutoItLibrary (1.1)
decorator (3.4.0)
pip (1.5.6)
pywin32 (220)
robotframework (2.8.7)
robotframework-ride (1.2.3)
robotframework-selenium2library (3.0.0)
robotframework-seleniumlibrary (3.3.1)
selenium (3.141.0)
setuptools (23.1.0)
urllib3 (1.25.3)

Log：

20190718 13:12:07.271 [WARN]: Importing test library "Selenium2Library" failed

Traceback (most recent call last):
Importing test library 'Selenium2Library' failed: ImportError: cannot import name is_string
Traceback (most recent call last):
  File "D:Python27libsite-packagesSelenium2Library\__init__.py", line 19, in <module>
    from SeleniumLibrary import SeleniumLibrary
  File "D:Python27libsite-packagesSeleniumLibrary\__init__.py", line 22, in <module>
    from SeleniumLibrary.base import DynamicCore
  File "D:Python27libsite-packagesSeleniumLibraryase\__init__.py", line 17, in <module>
    from .context import ContextAware
  File "D:Python27libsite-packagesSeleniumLibraryasecontext.py", line 17, in <module>
    from SeleniumLibrary.utils import escape_xpath_value
  File "D:Python27libsite-packagesSeleniumLibraryutils\__init__.py", line 22, in <module>
    from .types import is_falsy, is_noney, is_string, is_truthy, PY3
  File "D:Python27libsite-packagesSeleniumLibraryutils	ypes.py", line 21, in <module>
    from robot.utils import is_string
PYTHONPATH:
  D:Python27libsite-packages
obotidelib
obotlibraries
  D:Python27libsite-packages
obotidelib
  D:Python27libsite-packageswx-2.8-msw-unicode
  D:Python27libsite-packageswx-2.8-msw-unicode
  D:Python27libsite-packagessetuptools-23.1.0-py2.7.egg
  D:Python27libsite-packagesdecorator-3.4.0-py2.7.egg
  C:windowsSYSTEM32python27.zip
  D:Python27DLLs
  D:Python27lib
  D:Python27libplat-win
  D:Python27liblib-tk
  D:Python27
  D:Python27libsite-packages
  D:Python27libsite-packageswin32
  D:Python27libsite-packageswin32lib
  D:Python27libsite-packagesPythonwin
  .
  C:UserschenjyDesktop
  D:Python27libsite-packages
obotidespec
  File "D:Python27libsite-packages
obotidespeclibrarymanager.py", line 76, in _fetch_keywords
    return get_import_result(path, library_args)
  File "D:Python27libsite-packages
obotidespeclibraryfetcher.py", line 20, in get_import_result
    lib = TestLibrary(path, args)
  File "D:Python27libsite-packages
obotidelib
obot
unning	estlibraries.py", line 37, in TestLibrary
    libcode = importer.import_class_or_module(name)
  File "D:Python27libsite-packages
obotidelib
obotutilsimporter.py", line 64, in import_class_or_module
    self._raise_import_failed(name, err)
  File "D:Python27libsite-packages
obotidelib
obotutilsimporter.py", line 102, in _raise_import_failed
    raise DataError('
'.join(msg))