樹莓派的centos系統不帶有python3,雖然自己下載源碼編譯安裝，下面是方法：
1.安裝wget
yum -y install wget
2.使用wget命令從官方網站下載python3的源碼
wget https://www.python.org/ftp/python/3.5.7/Python-3.5.7.tgz
3.解壓
tar -zxvf Python-3.5.7.tgz
4.cd到解壓目錄，然后運行配置
./configure --prefix=/usr/local/python3 --with-ssl
5.make
6.make install
7.將編譯結果中的python可執行文件復制為python3,python3.5(這樣可以直接用python3來調用python3,而使用python時默認調用python2.7)
cd /usr/local/python3
cp python python3
cp python python3.5
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源碼編譯安裝的版本不帶有pip,下面介紹如何安裝pip
從pypi上下面pip壓縮包
wget https://files.pythonhosted.org/packages/36/fa/51ca4d57392e2f69397cd6e5af23da2a8d37884a605f9e3f2d3bfdc48397/pip-19.0.3.tar.gz
解壓
tar -zxvf pip-19.0.3.tar.gz
cd到解壓目錄，然后運行
python3 setup.py install
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將/usr/local/python3/bin添加至$PATH
vim /etc/profile
在文件末尾添加 PATH=$PATH:/usr/local/python3/bin:/usr/local/python3
source /etc/profile