Linux pip 升級失敗問題 （centos7）

要求：flask框架

1. 安裝pip指令

yum install python-pip -y

2. 安裝flask框架

pip install flask==1.9.0

Warning: 
    **You are using pip version 8.1.2, however version 10.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.**

3. 升級pip

pip install --upgrade pip

4. 二次安裝flask框架

pip install flask==1.9.0

Error:
Traceback (most recent call last):
    File "/usr/bin/pip", line 7, in <module>
    from pip._internal import main
ImportError: No module named _internal

5. 解決方法

# rm -rf /usr/lib/python2.7/site-packages/pip-10.0.1.dist-info
# yum install python-pip
# pip install --upgrade pip
# pip install flask==1.9.0