What is generator?

A generator is a special type of function that can produce a series of values over time instead of returning a single result all at once. It “yields” each value one by one, pausing its execution in between, and can later resume right where it left off.

Let's break it down

  • Function: Like any other function, a generator is defined with code that can run.
  • Yield: Instead of using return, a generator uses the yield keyword to hand back a value and temporarily stop.
  • State: When paused, the generator remembers its current position, local variables, and the loop it was in.
  • Iterator: Each time you ask the generator for the next item, it continues from its saved state and yields the next value.

Why does it matter?

Generators let you work with large or even infinite data streams without loading everything into memory. They make code cleaner for tasks that naturally produce items one after another, such as reading lines from a file, generating numbers, or processing data pipelines.

Where is it used?

  • Reading large files line‑by‑line.
  • Producing sequences like Fibonacci numbers or prime numbers.
  • Streaming data from APIs or sensors.
  • Implementing lazy evaluation in functional programming.
  • Building asynchronous pipelines where data arrives over time.

Good things about it

  • Memory efficient: Only one item is kept in memory at a time.
  • Lazy evaluation: Values are created only when needed.
  • Simple syntax: Often easier to write than manual iterator classes.
  • Supports infinite sequences: Can generate endless data without crashing.
  • Improves readability: Flow of data generation is clear and linear.

Not-so-good things

  • Single pass: Once exhausted, a generator cannot be rewound without recreating it.
  • Debugging can be tricky: Paused state may make tracing errors harder.
  • Limited language support: Not all programming languages have built‑in generator syntax.
  • Potential performance pitfalls: Overusing tiny yields can add overhead compared to batch processing.
  • Complex state: Complex generators with many variables can become hard to maintain.