CentOS7.x中pip3无法直接通过pip3命令使用、ipython3无法正常使用。

一、问题现象

1、通过pip -V查看版本

[root@localhost bin]# pip -V

显示如下：

pip 20.2b1 from /usr/lib/python2.7/site-packages/pip-20.2b1-py2.7.egg/pip (python 2.7)

[root@localhost bin]# pip3 -V

显示如下：

bash: /usr/bin/pip3: /usr/bin/python3: 坏的解释器: 没有那个文件或目录

在python3的安装目录/usr/local/python3/bin下用./pip3 -V命令查看版本:

[root@localhost bin]# ./pip3 -V

显示如下：

pip 20.1.1 from /usr/local/python3/lib/python3.8/site-packages/pip (python 3.8)

无法直接通过pip3 -V查看其版本，属于软链接的问题，解决过程如下：

[root@localhost bin]# pip3 -V
bash: /usr/bin/pip3: /usr/bin/python3: 坏的解释器: 没有那个文件或目录
[root@localhost bin]# pip -V
pip 20.2b1 from /usr/lib/python2.7/site-packages/pip-20.2b1-py2.7.egg/pip (python 2.7)
[root@localhost bin]# ln -s /usr/local/python3/bin/pip3 /usr/bin/pip3ln: 无法创建符号链接"/usr/bin/pip3": 文件已存在
[root@localhost bin]# rm /usr/bin/pip3
rm：是否删除普通文件 "/usr/bin/pip3"？y
[root@localhost bin]# ln -s /usr/local/python3/bin/pip3 /usr/bin/pip3
[root@localhost bin]# pip3 -V
pip 20.1.1 from /usr/local/python3/lib/python3.8/site-packages/pip (python 3.8)

2、通过ipython -V查看版本

[root@localhost bin]# ipython -V
3.2.1

在python3的安装目录/usr/local/python3/bin下用./ipython -V和./ipython3 -V查看，均返回如下异常：

Traceback (most recent call last):
File "./ipython3", line 5, in <module> from IPython import start_ipython ModuleNotFoundError: No module named 'IPython'

二、尝试解决

在/usr/local/python3/bin目录重新使用./pip3 install ipython安装：

[root@localhost bin]# ./pip3 install ipython
Requirement already satisfied: ipython in usr/local/python3/lib/python3.8/site-packages (6.1.0)

于是，接着尝试在/usr/local/python3/lib/python3.8/site-packages目录下，通过vi ipython-6.1.0-py3.8.egg-info修改Version: 6.1.0为Version: 6.1.111，发现再使用./pip3 install ipython安装，提示变为…(6.1.111)，由此可见，ipython-6.1.0-py3.8.egg-info文件在修复该问题过程中起了阻碍作用。
通过mv命令重命名这个文件，重新执行./pip3 install ipython后，通过./ipython3命令可以进入ipython3。
重新安装ipython及验证安装过程如下：

[root@localhost bin]# ./pip3 install ipythonCollecting ipython
Using cached ipython-7.16.1-py3-none-any.whl (785 kB)
Collecting jedi>=0.10
	Using cached jedi-0.17.2-py2.py3-none-any.whl (1.4 MB)
Requirement already satisfied: pygments in /usr/local/python3/lib/python3.8/site-packages (from ipython) (2.6.1)
Requirement already satisfied: prompt-toolkit!=3.0.0,!=3.0.1,<3.1.0,>=2.0.0 in /usr/local/python3/lib/python3.8/site-packages (from ipython) (3.0.5)
Collecting backcall
  Using cached backcall-0.2.0-py2.py3-none-any.whl (11 kB)
Requirement already satisfied: decorator in /usr/local/python3/lib/python3.8/site-packages (from ipython) (4.4.2)
Requirement already satisfied: pexpect; sys_platform != "win32" in /usr/local/python3/lib/python3.8/site-packages (from ipython) (4.8.0)
Requirement already satisfied: setuptools>=18.5 in /usr/local/python3/lib/python3.8/site-packages (from ipython) (41.2.0)
Requirement already satisfied: pickleshare in /usr/local/python3/lib/python3.8/site-packages (from ipython) (0.7.5)
Requirement already satisfied: traitlets>=4.2 in /usr/local/python3/lib/python3.8/site-packages (from ipython) (4.3.3)
Collecting parso<0.8.0,>=0.7.0
Using cached parso-0.7.0-py2.py3-none-any.whl (100 kB)
Requirement already satisfied: wcwidth in /usr/local/python3/lib/python3.8/site-packages (from prompt-toolkit!=3.0.0,!=3.0.1,<3.1.0,>=2.0.0->ipython) (0.2.5)
Requirement already satisfied: ptyprocess>=0.5 in /usr/local/python3/lib/python3.8/site-packages (from pexpect; sys_platform != "win32"->ipython) (0.6.0)
Requirement already satisfied: ipython-genutils in /usr/local/python3/lib/python3.8/site-packages (from traitlets>=4.2->ipython) (0.2.0)
Requirement already satisfied: six in /usr/local/python3/lib/python3.8/site-packages (from traitlets>=4.2->ipython) (1.15.0)
Installing collected packages: parso, jedi, backcall, ipython
Successfully installed backcall-0.2.0 ipython-7.16.1 jedi-0.17.2 parso-0.7.0
[root@localhost bin]# ./pip3 install ipython
Requirement already satisfied: ipython in /usr/local/python3/lib/python3.8/site-packages (7.16.1)
Requirement already satisfied: pygments in /usr/local/python3/lib/python3.8/site-packages (from ipython) (2.6.1)
Requirement already satisfied: jedi>=0.10 in /usr/local/python3/lib/python3.8/site-packages (from ipython) (0.17.2)
Requirement already satisfied: backcall in /usr/local/python3/lib/python3.8/site-packages (from ipython) (0.2.0)
Requirement already satisfied: pickleshare in /usr/local/python3/lib/python3.8/site-packages (from ipython) (0.7.5)
Requirement already satisfied: decorator in /usr/local/python3/lib/python3.8/site-packages (from ipython) (4.4.2)
Requirement already satisfied: prompt-toolkit!=3.0.0,!=3.0.1,<3.1.0,>=2.0.0 in /usr/local/python3/lib/python3.8/site-packages (from ipython) (3.0.5)
Requirement already satisfied: traitlets>=4.2 in /usr/local/python3/lib/python3.8/site-packages (from ipython) (4.3.3)
Requirement already satisfied: setuptools>=18.5 in /usr/local/python3/lib/python3.8/site-packages (from ipython) (41.2.0)
Requirement already satisfied: pexpect; sys_platform != "win32" in /usr/local/python3/lib/python3.8/site-packages (from ipython) (4.8.0)
Requirement already satisfied: parso<0.8.0,>=0.7.0 in /usr/local/python3/lib/python3.8/site-packages (from jedi>=0.10->ipython) (0.7.0)
Requirement already satisfied: wcwidth in /usr/local/python3/lib/python3.8/site-packages (from prompt-toolkit!=3.0.0,!=3.0.1,<3.1.0,>=2.0.0->ipython) (0.2.5)
Requirement already satisfied: six in /usr/local/python3/lib/python3.8/site-packages (from traitlets>=4.2->ipython) (1.15.0)
Requirement already satisfied: ipython-genutils in /usr/local/python3/lib/python3.8/site-packages (from traitlets>=4.2->ipython) (0.2.0)
Requirement already satisfied: ptyprocess>=0.5 in /usr/local/python3/lib/python3.8/site-packages (from pexpect; sys_platform != "win32"->ipython) (0.6.0)
[root@localhost bin]# ./ipython3
Python 3.8.3 (default, Jul 20 2020, 19:47:15) 
Type 'copyright', 'credits' or 'license' for more information
IPython 7.16.1 -- An enhanced Interactive Python. Type '?' for help.
In [1]: a = input()                                                      
2+3
In [2]: a                                                                
Out[2]: '2+3'

创建软链接(https://blog.csdn.net/xhx94/article/details/98865598)，并测试ipython3：

[root@localhost bin]# ln -s /usr/local/python3/bin/ipython3 /usr/bin/ipython3
[root@localhost bin]# ipython3
Python 3.8.3 (default, Jul 20 2020, 19:47:15) 
Type 'copyright', 'credits' or 'license' for more information
IPython 7.16.1 -- An enhanced Interactive Python. Type '?' for help.

In [1]: num = input('Please input a number:')                            
Please input a number:100+200

In [2]: num                                                              
Out[2]: '100+200'

三、原因分析

可能的原因是：多个python版本导致安装pip时出现版本混乱，以及使用pip install ipython命令安装时，版本选择也产生混乱。

四、向大神求助

如果哪位大神知晓问题的原因，欢迎留言指教，多谢！！

本文地址：https://blog.csdn.net/shinyolive/article/details/107479333