Generators in Python

What is a Generator?

A generator is a special type of iterator in Python that allows you to iterate over data without storing the entire sequence in memory. Generators are created using functions and the yield keyword. They are memory-efficient and lazy, meaning they produce items one at a time as needed.

Creating Generators

def my_generator():
    yield 1
    yield 2
    yield 3

gen = my_generator()
print(next(gen))  # Output: 1

Examples

# 1. Basic generator using yield
def count_up_to(n):
    count = 1
    while count <= n:
        yield count
        count += 1

for num in count_up_to(3):
    print(num)
# Output: 1 2 3
  

# 2. Using next() with a generator
gen = count_up_to(2)
print(next(gen))  # Output: 1
print(next(gen))  # Output: 2
# print(next(gen))  # Raises StopIteration
  

# 3. Generator expression (like list comprehension but with ())
squares = (x*x for x in range(5))
for square in squares:
    print(square)
# Output: 0 1 4 9 16
  

# 4. Memory efficiency
import sys

list_nums = [x for x in range(1000)]
gen_nums = (x for x in range(1000))

print(sys.getsizeof(list_nums))  # Larger memory
print(sys.getsizeof(gen_nums))   # Much smaller memory
  

# 5. Infinite generator
def infinite_numbers():
    num = 0
    while True:
        yield num
        num += 1

# To use safely, break manually
for i in infinite_numbers():
    if i > 3:
        break
    print(i)
# Output: 0 1 2 3