环境信息
操作系统：CentOS Linux 7 (Core)
Python：3.7.4

现状说明
当前CentOS系统自带了python2.7.5，因为yum会用到python2，所以不能删除，此次安装了python3之后就保持两个版本长期共存吧。

本次安装采用的是下载python源码再编译的方式；

操作步骤
以root身份登录CentOS，以下操作都在默认的~目录下：

1.yum 更新

yum update -y

2. 安装必要的软件

yum -y install \
zlib-devel \
bzip2-devel \
openssl-devel \
ncurses-devel \
sqlite-devel \
readline-devel \
tk-devel \
libffi-devel \
wget \
gcc \
make

3. 下载python 3.7.4源码：
我将源码存放到了/usr/local/python3目录中

mkdir /usr/local/python3
cd /usr/local/python3
wget https://www.python.org/ftp/python/3.7.4/Python-3.7.4.tgz

更多版本源码，请到https://www.python.org/ftp/python 中查找

4. 解压：

tar -zxvf Python-3.7.4.tgz

5. 进入解压后的目录，执行编译前的configure操作：

cd Python-3.7.4 && ./configure prefix=/usr/local/python3

6. 编译源码，在Python-3.7.4目录中执行以下命令：

make && make install

编译成功后提示如下信息，setuptools和pip都已经部署成功：

Collecting setuptools
Collecting pip
Installing collected packages: setuptools, pip
Successfully installed pip-19.0.3 setuptools-40.8.0

7. 创建python3的链接：

ln -s /usr/local/python3/bin/python3.7 /usr/bin/python3

8. 创建pip3的链接：

ln -s /usr/local/python3/bin/pip3 /usr/bin/pip3

9. pip3升级

pip3 install --upgrade pip

至此，安装完成，接下来简单验证一下

验证

1.简单操作如下，可见python3安装成功：

[root@python3 ~]# python3 --version
Python 3.7.4
[root@python3 ~]# pip3 --version
pip 19.3.1 from /usr/local/python3/lib/python3.7/site-packages/pip (python 3.7)
[root@python3 ~]# python3
Python 3.7.4 (default, Jul 20 2019, 11:35:19) 
[GCC 4.8.5 20150623 (Red Hat 4.8.5-36)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> 

按下Ctrl+d退出python3对话模式

2. 安装Flask：

pip3 install Flask

控制台输出以下信息，表示安装Flask成功：

[root@python3 ~]# pip3 install Flask
Collecting Flask
  Downloading https://files.pythonhosted.org/packages/9b/93/628509b8d5dc749656a9641f4caf13540e2cdec85276964ff8f43bbb1d3b/Flask-1.1.1-py2.py3-none-any.whl (94kB)
     |████████████████████████████████| 102kB 431kB/s 
Collecting itsdangerous>=0.24 (from Flask)
  Downloading https://files.pythonhosted.org/packages/76/ae/44b03b253d6fade317f32c24d100b3b35c2239807046a4c953c7b89fa49e/itsdangerous-1.1.0-py2.py3-none-any.whl
Collecting click>=5.1 (from Flask)
  Downloading https://files.pythonhosted.org/packages/fa/37/45185cb5abbc30d7257104c434fe0b07e5a195a6847506c074527aa599ec/Click-7.0-py2.py3-none-any.whl (81kB)
     |████████████████████████████████| 81kB 1.3MB/s 
Collecting Jinja2>=2.10.1 (from Flask)
  Downloading https://files.pythonhosted.org/packages/1d/e7/fd8b501e7a6dfe492a433deb7b9d833d39ca74916fa8bc63dd1a4947a671/Jinja2-2.10.1-py2.py3-none-any.whl (124kB)
     |████████████████████████████████| 133kB 1.8MB/s 
Collecting Werkzeug>=0.15 (from Flask)
  Downloading https://files.pythonhosted.org/packages/d1/ab/d3bed6b92042622d24decc7aadc8877badf18aeca1571045840ad4956d3f/Werkzeug-0.15.5-py2.py3-none-any.whl (328kB)
     |████████████████████████████████| 337kB 3.4MB/s 
Collecting MarkupSafe>=0.23 (from Jinja2>=2.10.1->Flask)
  Downloading https://files.pythonhosted.org/packages/98/7b/ff284bd8c80654e471b769062a9b43cc5d03e7a615048d96f4619df8d420/MarkupSafe-1.1.1-cp37-cp37m-manylinux1_x86_64.whl
Installing collected packages: itsdangerous, click, MarkupSafe, Jinja2, Werkzeug, Flask
Successfully installed Flask-1.1.1 Jinja2-2.10.1 MarkupSafe-1.1.1 Werkzeug-0.15.5 click-7.0 itsdangerous-1.1.0

3. 创建 hello.py 文件，内容如下：

from flask import Flask

app = Flask(__name__)

@app.route('/')
def hello():
        return 'Hello flask'

if __name__ == '__main__':
        app.run(host='0.0.0.0',port=5000,debug=True)

4. 运行脚本：

python3 hello.py

5. 通过浏览器访问服务器地址：

如果无法访问，请关闭linux防火墙，详细请参考：

linux关闭防火墙