为什么pip不安装当前版本的包？

Question

我无法通过 pip 安装当前版本的 pydot（1.0.28）。虽然 yolk 和 PyPi 都显示这个版本是可用的最新版本，

但是当我输入

pip -U pydot

却得到了

Requirement already up-to-date: pydot in /Library/Python/2.7/site-packages
Requirement already up-to-date: pyparsing in /Library/Python/2.7/site-packages (from pydot)
Requirement already up-to-date: setuptools in /Library/Python/2.7/site-packages (from pydot)

即使我强制指定当前版本，输入

pip -U pydot==1.0.28

也得到了

Downloading/unpacking pydot==1.0.28
  Could not find a version that satisfies the requirement pydot==1.0.28 (from versions: 1.0.2)
  Some externally hosted files were ignored (use --allow-external to allow).
Cleaning up...
No distributions matching the version for pydot==1.0.28

甚至当我尝试

pip -U --allow-external pydot pydot==1.0.28

也还是得到了

Downloading/unpacking pydot==1.0.28
  Could not find a version that satisfies the requirement pydot==1.0.28 (from versions: 1.0.2)
  Some insecure and unverifiable files were ignored (use --allow-unverified pydot to allow).
Cleaning up...
No distributions matching the version for pydot==1.0.28

Answer 1

试试这个：

pip install --allow-unverified pydot pydot==1.0.28