问题：如何查看pip已经安装的软件包及版本号？
解决：使用pip freeze命令
方法：
pip freeze命令按需要的格式显示已经安装的包
更多内容可以使用pip -h显示pip的其它命令
Commands:
install Install packages.
download Download packages.
uninstall Uninstall packages.
freeze Output installed packages in requirements format.
list List installed packages.
show Show information about installed packages.
check Verify installed packages have compatible dependencies.
search Search PyPI for packages.
wheel Build wheels from your requirements.
hash Compute hashes of package archives.
completion A helper command used for command completion.
help Show help for commands.