Final answer:
The %lprun magic command is used in IPython for line-by-line performance profiling of functions, helping developers to optimize code by providing detailed execution time metrics for each line of code.
Step-by-step explanation:
The %lprun magic command is a feature in the IPython environment, which is designed for performance profiling of individual functions. When you invoke this command before a function call, it provides detailed information on the function's execution time, helping developers identify parts of the code that may require optimization for better performance. Each line of the specified function is profiled, and the summary includes metrics such as the number of times each line was executed, the time each line took, and what percentage of the total execution time was spent on each line.