Final answer:
External lookups can be in various formats such as Python, CSV, exe, or binary, each serving different purposes. CSVs are commonly used for their simplicity and interoperability with different systems.
Step-by-step explanation:
External lookups, especially in the context of software development and configuration management, must typically be in a format that can be read and processed by the relevant program. Options like Python scripts, CSV files, .exe (executable files), and other binary formats serve different purposes. For instance, Python scripts can be used for more complex data processing tasks, where a CSV might be used for simpler, table-like data and executables could be used for system-level operations. It is important to choose the correct format based on the needs of the software system. Without additional context, it's challenging to determine the specific requirement, but usually, CSV's are particularly common for data lookups because of their simplicity and interoperability with various systems.