需要看你是否安装python3还是python2

sudo yum install certbot python2-certbot-nginx
sudo yum install certbot python3-certbot-nginx

$ sudo yum install certbot python2-certbot-nginx

Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
Package certbot-1.11.0-2.el7.noarch already installed and latest version
Resolving Dependencies
--> Running transaction check
---> Package python2-certbot-nginx.noarch 0:1.11.0-1.el7 will be installed
--> Processing Dependency: pyparsing >= 1.5.5 for package: python2-certbot-nginx-1.11.0-1.el7.noarch
--> Running transaction check
---> Package pyparsing.noarch 0:1.5.6-9.el7 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

=====================================================================================================================================================================================
 Package                                              Arch                                  Version                                        Repository                           Size
=====================================================================================================================================================================================
Installing:
 python2-certbot-nginx                                noarch                                1.11.0-1.el7                                   epel                                 78 k
Installing for dependencies:
 pyparsing                                            noarch                                1.5.6-9.el7                                    base                                 94 k

Transaction Summary
=====================================================================================================================================================================================
Install  1 Package (+1 Dependent package)

Total download size: 172 k
Installed size: 633 k
Is this ok [y/d/N]: y
Downloading packages:
(1/2): pyparsing-1.5.6-9.el7.noarch.rpm                                                                                                                       |  94 kB  00:00:00     
(2/2): python2-certbot-nginx-1.11.0-1.el7.noarch.rpm                                                                                                          |  78 kB  00:00:00     
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Total                                                                                                                                                420 kB/s | 172 kB  00:00:00     
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
  Installing : pyparsing-1.5.6-9.el7.noarch                                                                                                                                      1/2 
  Installing : python2-certbot-nginx-1.11.0-1.el7.noarch                                                                                                                         2/2 
  Verifying  : python2-certbot-nginx-1.11.0-1.el7.noarch                                                                                                                         1/2 
  Verifying  : pyparsing-1.5.6-9.el7.noarch                                                                                                                                      2/2 

Installed:
  python2-certbot-nginx.noarch 0:1.11.0-1.el7                                                                                                                                        

Dependency Installed:
  pyparsing.noarch 0:1.5.6-9.el7                                                                                                                                                     

Complete!