Comprehensions & generators
List/dict/set comprehensions, generator expressions, and lazy iteration.
Batch Rows in Chunks with a Generator in Python
Group a list of row dicts into fixed-size chunks using a generator that yields one slice per call.
from typing import Iterator, List
def batch_rows(rows: List[dict], batch_size: int) -> Iterator[List[dict]]:
for i in range(0, len(rows), batch_size):
yield rows[i:i + batch_size]
if __name__ == "__main__":
sample_rows = [
{"id": 1, "name": "Alice"},
{"id": 2, "name": "Bob"},
…Generate UUID4 Values with a Python Generator
This code defines a generator function that yields mock UUID4 values, allowing you to stream unique identifiers one at a time.
import uuid
def generate_uuids(count=5):
"""Generate a stream of mock UUID4 values."""
for _ in range(count):
yield uuid.uuid4()
if __name__ == "__main__":
# Generate and print 5 UUIDs
for uid in generate_uuids(5):
print(uid)Generator Function to Yield an Infinite Counter in Python
This code demonstrates a generator function that yields an infinite sequence of integers starting from a given value, allowing lazy, memory-efficient iteration.
def infinite_counter(start=0):
count = start
while True:
yield count
count += 1
if __name__ == "__main__":
counter = infinite_counter(5)
for _ in range(5):
print(next(counter))How to Close a Generator and Handle GeneratorExit in Python
This Python code demonstrates how to explicitly close a generator using the close() method and handle the GeneratorExit exception through a finally block to run cleanup logic.
def countdown(n):
try:
while n > 0:
yield n
n -= 1
finally:
print(f"Generator closed after countdown completed")
if __name__ == "__main__":
gen = countdown(5)
print(next(gen))
print(next(gen))
gen.close()
print("Generator closed explicitly")How to Compress a Generator with a Boolean Mask in Python
Filters items from a generator based on a parallel boolean mask, yielding only the items where the mask is True.
def compress(generator, mask):
for item, keep in zip(generator, mask):
if keep:
yield item
if __name__ == "__main__":
data = [1, 2, 3, 4, 5]
mask = [True, False, True, False, True]
result = list(compress(iter(data), mask))
print(result)How to Generate Combinations with Replacement in Python
Generate all r-length combinations with repetition from a list using the standard library itertools.combinations_with_replacement function.
from itertools import combinations_with_replacement
items = ['A', 'B', 'C']
r = 2
combos = list(combinations_with_replacement(items, r))
for combo in combos:
print(combo)
if __name__ == "__main__":
print(f"Total combinations with replacement: {len(combos)}")How to Generate Permutations of Length r in Python
Generate all ordered arrangements of length r from a given list of elements using itertools.permutations.
from itertools import permutations
def generate_permutations(elements, r):
"""Generate all r-length permutations of the given elements."""
return list(permutations(elements, r))
if __name__ == "__main__":
elements = ['A', 'B', 'C']
r = 2
result = generate_permutations(elements, r)
print(f"Ele…How to generate combinations in Python with itertools
Generate all unique combinations of r items from a given list using itertools.combinations.
import itertools
def combinations_generator(items, r):
return list(itertools.combinations(items, r))
if __name__ == "__main__":
items = ['A', 'B', 'C', 'D']
r = 2
result = combinations_generator(items, r)
for combo in result:
print(combo)
print(f"Total: {len(result)} combinations of {…How to stream parse JSON arrays in Python
This code demonstrates two generators: one that streams a JSON array as individual chunks, and another that incrementally parses those chunks into Python objects using json.JSONDecoder.
import json
def json_array_stream(items):
"""Generator that yields JSON-encoded values one at a time."""
yield "["
for i, item in enumerate(items):
if i > 0:
yield ","
yield json.dumps(item)
yield "]"
def parse_json_stream(stream):
"""Consumes a stream of JSON fragme…Browse by section
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Comprehensions & generators — Python code examples
What you will find here
This page collects comprehensions & generators snippets — short, copy-ready Python you can paste into our free online IDE and run without installing anything. Each sample includes a plain-English explanation and the full source code.
Samples vs tutorials and challenges
Samples are quick reference — one concept per page. For step-by-step teaching, use our Python tutorials. To test yourself, try quizzes or coding challenges. Clean up style with the Python formatter.