問題解決：NameError: name 'platform_system' is not defined

問題場景

使用 pip安裝依賴的時候，更新之後，更新的依賴不能用。比如我將機器的ansible版本指定安裝2.7.11版本，安裝成功之後，使用命令ansible --version的時候，提示報錯，報錯具體提示如下：

ERROR! Unexpected Exception, this is probably a bug: name 'platform_system' is not defined
the full traceback was:

Traceback (most recent call last):
  File "/bin/ansible", line 97, in <module>
    mycli = getattr(__import__("ansible.cli.%s" % sub, fromlist=[myclass]), myclass)
  File "/usr/lib/python2.7/site-packages/ansible/cli/__init__.py", line 38, in <module>
    from ansible.inventory.manager import InventoryManager
  File "/usr/lib/python2.7/site-packages/ansible/inventory/manager.py", line 38, in <module>
    from ansible.plugins.loader import inventory_loader
  File "/usr/lib/python2.7/site-packages/ansible/plugins/loader.py", line 22, in <module>
    from ansible.parsing.utils.yaml import from_yaml
  File "/usr/lib/python2.7/site-packages/ansible/parsing/utils/yaml.py", line 17, in <module>
    from ansible.parsing.yaml.loader import AnsibleLoader
  File "/usr/lib/python2.7/site-packages/ansible/parsing/yaml/loader.py", line 30, in <module>
    from ansible.parsing.yaml.constructor import AnsibleConstructor
  File "/usr/lib/python2.7/site-packages/ansible/parsing/yaml/constructor.py", line 29, in <module>
    from ansible.parsing.vault import VaultLib
  File "/usr/lib/python2.7/site-packages/ansible/parsing/vault/__init__.py", line 42, in <module>
    from cryptography.hazmat.backends import default_backend
  File "/usr/lib64/python2.7/site-packages/cryptography/hazmat/backends/__init__.py", line 7, in <module>
    import pkg_resources
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 3007, in <module>
    working_set.require(__requires__)
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 728, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 631, in resolve
    requirements.extend(dist.requires(req.extras)[::-1])
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 2489, in requires
    dm = self._dep_map
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 2700, in _dep_map
    self.__dep_map = self._compute_dependencies()
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 2733, in _compute_dependencies
    common = frozenset(reqs_for_extra(None))
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 2730, in reqs_for_extra
    if req.marker_fn(override={'extra':extra}):
  File "/usr/lib/python2.7/site-packages/_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

問題環境

軟件	版本
python	2.7
pip	8.1.2
setuptools	0.9.8

問題原因

指定軟件版本進行更新的時候，軟件本身依賴的setuptools版本不兼容當前機器的版本。所以更新setuptools依賴即可。不過爲了保險起見，最好連pip都一起更新。

解決方案

使用root用戶執行以下命令

pip install --upgrade pip
pip install --upgrade setuptools

結果

使用命令ansible --version命令之後，可以正常顯示，如下：

ansible 2.7.11
  config file = /home/tidb/tidb-ansible/ansible.cfg
  configured module search path = [u'/home/tidb/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python2.7/site-packages/ansible
  executable location = /bin/ansible
  python version = 2.7.5 (default, Oct 30 2018, 23:45:53) [GCC 4.8.5 20150623 (Red Hat 4.8.5-36)]

總結

版本依賴衝突是一個比較常見的問題，主要是分析背後的依賴問題，根據具體情況即可解決問題。

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