Iterator vs Generator in Python: What's the Difference?

Hi Pythonistas

We have already discussed what is iterator and what is generator in previous post. Today we are going the learn what is the difference between them

Key Differences Between Iterator and Generator

Feature	Iterator	Generator
How it's created	Manually using a class with `__iter__` and `__next__`	Using a function with `yield` or generator expression
Syntax	Verbose, boilerplate	Clean and concise
Memory Efficiency	May store full data in memory	Produces values lazily (one at a time)
Use Case	Custom iteration logic	Lazy sequences, large data, streams

Let us check the lazy evaluation of generator with a example

import tracemalloc

def using_iterator():
    nums = iter([x for x in range(10**6)]) 
    return sum(nums)

def using_generator():
    nums = (i for i in range(10**6))
    return sum(nums)

tracemalloc.start()  # Start tracking memory
sum_ = using_iterator()  # Run the function
# Get memory usage statistics
current, peak = tracemalloc.get_traced_memory()
print("using using iterator")
print(f"Current memory usage: {current / 1024**2:.10f} MB")
print(f"Peak memory usage: {peak / 1024**2:.4f} MB")
tracemalloc.stop()  # Stop tracking


tracemalloc.start()  # Start tracking memory
sum_ = using_generator()  # Run the function
# Get memory usage statistics
current, peak = tracemalloc.get_traced_memory()
print("\nusing using generator")
print(f"Current memory usage: {current / 1024**2:.10f} MB")
print(f"Peak memory usage: {peak / 1024**2:.4f} MB")
tracemalloc.stop()  # Stop tracking

Output

using using iterator
Current memory usage: 0.0000305176 MB
Peak memory usage: 34.7535 MB

using using generator
Current memory usage: 0.0000305176 MB
Peak memory usage: 0.0003 MB

We can see that current memory for the both function is same because they return same data but difference is the peak

memmory usage we can see that peak memory for iterator is 34.7535MB but for generator it only 0.0003MB.

When to Use What?

Scenario	Go With
You need to write a simple, lazy iterable	Generator
You need full control over state & iteration logic	Iterator
You want better memory usage	Generator

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