Code not difficult, mainly to learn FTP file transfer and manipulation.

代码没有什么难度，主要是为了学习FTP传输和文件操控。

youdao

Fixing the QR code shortcomings will not be easy as it is always difficult to change the philosophies of marketers that have been using the same strategies for years.

FORBES: Why QR Codes Don't Work

While some of the deployed protocols are in the public domain, the source code for particular applications have not been released yet making it difficult for security researchers to render an informed opinion on its implementation.

FORBES: Pressure Increases On Silent Circle To Release Application Source Code

Brazil's forgiving labour code, which makes it difficult to fire public servants, has not helped.

ECONOMIST: Brazil