Yields and List in Python

In this article, i will compare two common ways to return a sequence of values from a function is using yield to create a generator and returning a list.

What is List returning?

Returning a list from a function is returning a sequence of values (list of integers, list of strings, etc). The caller receives the fully constructed and can iterate over it or manipulate it as needed.

def return_list(nums):
    res = []
    for i in range(nums):
        res.append(i)
    return res

my_list = return_list(5)
print(my_list) 
# Output: [0, 1, 2, 3, 4]        

What is yield?

yield is a keyword in Python used to create a generator. It allows a function return a value and pause its execution, saving its state for later resumption. When the function is called, it returns a generator object which can be iterated over to retrieve values one at a time.

def generate_numbers(nums):
    for i in range(nums):
        yield i

my_yield = generate_numbers(5)
for num in my_yield:
    print(num, end=' ')
#Output: 0 1 2 3 4         

What is the difference?

Memory usage:

• yield: Generators created with yield are memory efficient. They produce items one at a time, only when required, which is ideal for large datasets
• Returning a list: When returning a list from a function, the entire list is stored in memory.

Performance:

• yield: Good for large datasets since because it don't require the entire dataset to be stored in memory
• Returning a list: Large datasets may cause list-returning functions to slow, but they are good for situations where the complete sequence is needed up front.

Easy to use:

• yield: Using yield can be more complex, might be less intuitive initially, and might not be friendly for beginners
• Returning a list: Straightforward, providing a complete dataset for immediate use.

Conclusion

Choosing the right method depends on the specific requirements of your tasks, particularly regarding memory usage, performance, and ease of use. Understanding both methods is an important skill for any Python developer.