问题场景

使用​​pip​​​安装依赖的时候，更新之后，更新的依赖不能用。比如我将机器的​​ansible​​​版本指定安装​​2.7.11​​​版本，安装成功之后，使用命令​​ansible --version​​的时候，提示报错，报错具体提示如下：

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ERROR! Unexpected Exception, this is probably a bug: name "platform_system" is not definedthe full traceback was:Traceback (most recent call last):  File "/bin/ansible", line 97, in     mycli = getattr(__import__("ansible.cli.%s" % sub, fromlist=[myclass]), myclass)  File "/usr/lib/python2.7/site-packages/ansible/cli/__init__.py", line 38, in     from ansible.inventory.manager import InventoryManager  File "/usr/lib/python2.7/site-packages/ansible/inventory/manager.py", line 38, in     from ansible.plugins.loader import inventory_loader  File "/usr/lib/python2.7/site-packages/ansible/plugins/loader.py", line 22, in     from ansible.parsing.utils.yaml import from_yaml  File "/usr/lib/python2.7/site-packages/ansible/parsing/utils/yaml.py", line 17, in     from ansible.parsing.yaml.loader import AnsibleLoader  File "/usr/lib/python2.7/site-packages/ansible/parsing/yaml/loader.py", line 30, in     from ansible.parsing.yaml.constructor import AnsibleConstructor  File "/usr/lib/python2.7/site-packages/ansible/parsing/yaml/constructor.py", line 29, in     from ansible.parsing.vault import VaultLib  File "/usr/lib/python2.7/site-packages/ansible/parsing/vault/__init__.py", line 42, in     from cryptography.hazmat.backends import default_backend  File "/usr/lib64/python2.7/site-packages/cryptography/hazmat/backends/__init__.py", line 7, in     import pkg_resources  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 3007, in     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 "", line 1, in NameError: name "platform_system" is not defined

问题环境

问题原因

指定软件版本进行更新的时候，软件本身依赖的​​setuptools​​​版本不兼容当前机器的版本。所以更新​​setuptools​​​依赖即可。不过为了保险起见，最好连​​pip​​都一起更新。

解决方案

使用​​root​​用户执行以下命令

pip install --upgrade pippip install --upgrade setuptools

结果

使用命令​​ansible --version​​命令之后，可以正常显示，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)]

总结

版本依赖冲突是一个比较常见的问题，主要是分析背后的依赖问题，根据具体情况即可解决问题。

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