Programming Languages
Python
Python in a Nutshell is a comprehensive Python reference to have on your desk while developing any sort of Python application.
Python testing with pytest covers pytest framework and related testing best practices in the Python ecosystem.
Fluent Python is a useful guide to writing effective, idiomatic Python code. This book is recommended reading for intermediate Python developers and those coming from other languages, showing how Python features and idioms should be used most effectively.
C++
Effective C++ contains useful recipes for sound implementations of common C++ patterns.
Effective STL focuses on the correct usage of the standard teamplate library.
Effective Modern C++ follows from the previous series, expanding on the transition to C++11 and C++14 and their new constructs.