What is Generator in Python With Example?

A generator is a special type of iterator that allows you to create iterable sequences of data dynamically. Unlike regular functions that return a value and terminate, generators use the “yield” keyword to produce a series of values, one at a time, whenever requested. This makes them memory-efficient and useful for handling large datasets or infinite sequences.

Here’s an example of a simple generator function that generates a sequence of squares:

def square_generator(n):
    for i in range(n):
        yield i ** 2

# Using the generator to create a sequence of squares
squares = square_generator(5)

# Now, you can iterate through the generator to get the values one at a time
for square in squares:



In this example, the square_generator function is defined with the yield statement inside a loop. When the generator is called, it starts executing the function until it reaches the yield statement. At this point, the current value (i ** 2) is yielded to the caller, and the function’s state is saved. The next time the generator is called, it resumes execution from the last yield statement and continues until the next yield.

Generators are particularly useful when you have a large dataset or an infinite sequence that you want to process one item at a time, without having to store the entire sequence in memory. They provide an elegant way to generate data on-the-fly while maintaining efficient memory usage.

What is the difference between Python generator and Python function?

Python generators and functions are both used to define blocks of code that can be executed when called, but they serve different purposes and have some key differences:

  1. Execution Flow:
    • Functions: Functions execute from start to finish, and they can be called multiple times. Each time a function is called, it starts execution from the beginning.
    • Generators: Generators use the yield statement to produce values lazily and maintain their state between calls. They can be paused and resumed, allowing incremental computation of values. Generators maintain their internal state between iterations.
  2. Memory Usage:
    • Functions: Functions execute and return values. If a function generates a list of values, all the values are usually stored in memory at once, which can be memory-intensive for large datasets.
    • Generators: Generators yield values one at a time, and they don’t store all values in memory simultaneously. This makes generators memory-efficient, especially when dealing with large sequences of data.
  3. Iteration:
    • Functions: Functions are not designed for iteration by default. If you want to iterate through the values generated by a function, you need to create a container (like a list) to store the values returned by successive calls.
    • Generators: Generators are designed for iteration. They are iterable objects that produce values using the yield statement. You can use them in loops directly without the need to store the entire sequence.
  4. Lazy Evaluation:
    • Functions: Functions eagerly execute and return their result. If a function generates a sequence of values, it computes all the values before returning them.
    • Generators: Generators provide lazy evaluation. They only compute and yield the next value in the sequence when requested. This allows for efficient memory usage and is particularly useful for processing streams of data.
  5. Use Cases:
    • Functions: Functions are used for encapsulating reusable blocks of code. They are suitable for calculations, data processing, and general-purpose programming tasks.
    • Generators: Generators are used when you want to create a sequence of values efficiently without loading all of them into memory at once. They are great for handling large datasets, streams, and any situation where lazy evaluation is beneficial.

Why use generator instead of list Python?

Using a generator instead of a list in Python has several advantages, especially when dealing with large datasets or scenarios where memory efficiency and lazy evaluation are important. Here are some reasons why you might prefer using a generator:

  1. Memory Efficiency: Generators yield values one at a time as they are requested, without storing the entire sequence in memory. This is particularly beneficial when dealing with large datasets that might not fit into memory all at once.
  2. Lazy Evaluation: Generators provide lazy evaluation, meaning that they only compute and yield the next value in the sequence when needed. This can improve performance by avoiding unnecessary computations and reducing the time it takes to start processing the data.
  3. Efficient Iteration: Generators are designed for efficient iteration. They work seamlessly in loops and other constructs that expect an iterable. This eliminates the need to create a separate list to store all the values, which can save memory and processing time.
  4. Infinite Sequences: Generators can represent infinite sequences, such as an infinite series of numbers or an endless stream of data. Trying to create a list with an infinite number of elements would be impossible and wasteful.
  5. Stream Processing: If you’re working with data that is read from a file, network stream, or some external source, generators can process this data incrementally as it becomes available, rather than waiting to read and process the entire dataset before starting.
  6. Performance: Because generators provide values one at a time and only compute what’s necessary, they can lead to better performance in situations where you’re dealing with complex or time-consuming computations.
  7. Reduced Initialization Time: Creating a generator requires less initialization time compared to building a complete list, which can be important in time-sensitive applications.
  8. Dynamic Data: Generators can handle cases where the data size is not known in advance. As the generator produces values on-the-fly, you don’t need to preallocate memory or worry about resizing arrays.

However, it’s important to note that generators have limitations as well:

  • Generators are one-time use: Once you’ve iterated through a generator, you can’t restart the iteration from the beginning. You would need to recreate the generator if you want to iterate again.
  • Generators can be slower than direct list manipulation for small datasets, due to the overhead of function calls and the need to repeatedly compute values.

If you’re working with large datasets, streams of data, or scenarios where memory efficiency and incremental processing are important, generators are a powerful tool to consider. For

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  • Yaryna Ostapchuk

    I am an enthusiastic learner and aspiring Python developer with expertise in Django and Flask. I pursued my education at Ivan Franko Lviv University, specializing in the Faculty of Physics. My skills encompass Python programming, backend development, and working with databases. I am well-versed in various computer software, including Ubuntu, Linux, MaximDL, LabView, C/C++, and Python, among others.

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