Python Code
Samples
Copy-ready Python snippets by topic and difficulty — short, focused, and runnable in the browser editor.
How to Group Data by Category in Python with a Split Data Helper
This code groups a list of (category, item) pairs into a dictionary where each key is a category and each value is a list of items belonging to that category.
def split_data(categories):
"""
Group data items into buckets based on a key function.
Returns a dict where keys are bucket names and values are lists of items.
"""
buckets = {}
for category, item in categories:
if category not in buckets:
buckets[category] = []
buck…How to Create an Iterable Class with __iter__ and __next__ in Python
Build custom iterable classes in Python by implementing the __iter__ and __next__ dunder methods to yield items on demand.
class EvenNumbers:
def __init__(self, limit):
self.limit = limit
self.current = 0
def __iter__(self):
return self
def __next__(self):
if self.current >= self.limit:
raise StopIteration
result = self.current
self.current += 2
return resul…How to Implement Iterator Protocol on a Custom Class in Python
Create a custom iterable class by defining the __iter__ and __next__ methods, enabling use in for loops and list conversions.
class Countdown:
"""Iterator that counts down from start to 0."""
def __init__(self, start):
self.start = start
self.current = start
def __iter__(self):
return self
def __next__(self):
if self.current < 0:
raise StopIteration
value = self.current
…Drop Elements From Start While Condition Is True in Python
This generator function drops elements from the beginning of an iterable while a predicate returns true, then yields the rest.
def drop_while(predicate, iterable):
"""Drop elements from the start while predicate is true."""
it = iter(iterable)
for item in it:
if not predicate(item):
yield item
break
yield from it
if __name__ == "__main__":
numbers = [1, 2, 3, 4, 1, 2, 5]
result = list(d…Find the First Index Where a Condition Is True in Python
Search any iterable for the first element matching a predicate and return its index, or -1 if none match.
def first_true_index(items, condition):
"""Return the first index where condition(item) is True, or -1 if none match."""
for i, item in enumerate(items):
if condition(item):
return i
return -1
if __name__ == "__main__":
numbers = [1, 3, 5, 8, 10, 12]
# Find first number greate…Take While Predicate True From Start in Python
Create a custom take_while function that collects elements from an iterable until a predicate returns False, then stops.
def take_while(predicate, iterable):
"""Return elements from iterable until the predicate becomes False."""
result = []
for item in iterable:
if predicate(item):
result.append(item)
else:
break
return result
if __name__ == "__main__":
numbers = [2, 4, 6, 7,…Chunk an Iterable into Batches with a Generator in Python
Yield fixed-size batches from any iterable lazily using itertools.islice inside a generator function.
from itertools import islice
def chunked(iterable, size):
iterator = iter(iterable)
while True:
batch = list(islice(iterator, size))
if not batch:
break
yield batch
if __name__ == "__main__":
data = range(10)
for batch in chunked(data, 3):
print(batch)Cycle an iterable forever in Python
Define a generator that repeatedly yields items from an iterable, cycling back to the beginning infinitely.
def cycle_generator(iterable):
"""Yield items from iterable forever, cycling back to the start."""
items = list(iterable) # Convert to list so it can restart
index = 0
while True:
yield items[index]
index = (index + 1) % len(items)
if __name__ == "__main__":
colors = ["red", "gre…Drop n items then yield rest generator
A generator that skips the first n items of an iterable and then yields the remaining items one by one.
def drop(n, items):
"""Yield every item except the first n from items."""
it = iter(items)
for _ in range(n):
next(it, None) # skip first n items
yield from it
if __name__ == "__main__":
numbers = [10, 20, 30, 40, 50]
result = list(drop(2, numbers))
print(result)How to Accumulate Values with a Generator in Python
This generator yields the running total of an iterable's elements, producing a cumulative sum with each step.
def accum(iterable):
total = 0
for item in iterable:
total += item
yield total
# Demo
if __name__ == "__main__":
data = [1, 2, 3, 4, 5]
print(list(accum(data))) # [1, 3, 6, 10, 15]
# Also works with any iterable, e.g., range
print(list(accum(range(1, 6)))) # [1, 3, 6, 10, 15]How to Create a Pairwise Generator with zip and tee in Python
Build a memory-efficient generator that yields successive overlapping pairs from any iterable using zip and tee.
from itertools import tee
def pairwise(iterable):
"""Yield successive overlapping pairs from iterable."""
a, b = tee(iterable)
next(b, None)
return zip(a, b)
if __name__ == "__main__":
values = [1, 2, 3, 4, 5]
print(list(pairwise(values)))
print(list(pairwise("hello")))How to Generate Cartesian Product Combinations in Python
Use itertools.product to generate every combination across multiple iterables, a pattern common for product variant generation.
from itertools import product
def generate_cartesian_combinations(*iterables):
"""Generate all Cartesian product combinations of given iterables."""
return list(product(*iterables))
if __name__ == "__main__":
colors = ["red", "green", "blue"]
sizes = ["S", "M", "L"]
styles = ["t-shirt", "hoodie"]…How to Implement takewhile Generator in Python
A generator that yields items from an iterable until a condition fails, like itertools.takewhile.
def takewhile(predicate, iterable):
for item in iterable:
if not predicate(item):
break
yield item
if __name__ == "__main__":
numbers = [1, 2, 3, 4, 5, 1, 2, 3]
result = list(takewhile(lambda x: x < 4, numbers))
print(result)How to Lazily Transform Items in Python with a Generator
Map a transform function over an iterable lazily with a generator so items are processed on demand, not up front.
def lazy_map(items, transform):
for item in items:
yield transform(item)
def double(x):
return x * 2
def upper(s):
return s.upper()
if __name__ == "__main__":
numbers = [1, 2, 3, 4, 5]
doubled = lazy_map(numbers, double)
print("Doubled numbers:", end=" ")
for value in doubled:
…How to Merge Multiple Iterables with a Generator in Python
This code defines a generator function that 'chains' or merges multiple iterables into a single iterator, which is then converted to a list.
def chain(*iterables):
for iterable in iterables:
yield from iterable
def main():
list1 = [1, 2, 3]
tuple1 = (4, 5)
set1 = {6, 7}
string1 = "89"
result = list(chain(list1, tuple1, set1, string1))
print(result)
if __name__ == "__main__":
main()How to Slice a Generator with islice in Python
Use itertools.islice to take the first n items from any iterable without materializing the whole sequence into a list.
from itertools import islice
def first_n(iterable, n):
"""Return the first n items from an iterable."""
return list(islice(iterable, n))
if __name__ == "__main__":
numbers = range(10, 100) # large iterable
result = first_n(numbers, 5)
print(result) # [10, 11, 12, 13, 14]How to Use starmap() to Unpack Tuple Arguments in Python
Use itertools.starmap to apply a function to each tuple in an iterable, unpacking tuple elements as separate arguments and returning an iterator of results.
from itertools import starmap
def multiply(a, b):
return a * b
if __name__ == "__main__":
pairs = [(2, 3), (4, 5), (6, 7), (8, 9)]
results = list(starmap(multiply, pairs))
print(results)How to filter a generator with a predicate function in Python
This code defines a generator function that yields only items from an iterable that satisfy a given predicate, then tests it with even and positive number filters.
def filter_gen(predicate, iterable):
for item in iterable:
if predicate(item):
yield item
def is_even(num):
return num % 2 == 0
def is_positive(num):
return num > 0
if __name__ == "__main__":
numbers = range(-5, 10)
even_numbers = list(filter_gen(is_even, numbers))
p…How to Use multiprocessing Pool map and starmap in Python
Parallelize functions over iterables with Pool.map, and unpack multiple arguments via Pool.starmap.
from multiprocessing import Pool
def square(x):
return x * x
def add_and_multiply(a, b, c):
return (a + b) * c
if __name__ == "__main__":
numbers = [1, 2, 3, 4, 5]
with Pool(processes=2) as pool:
squares = pool.map(square, numbers)
print(f"squares: {squares}")
starmap_arg…Browse by section
Each section groups closely related Python snippets.
Guide: free Python code samples library
Copy-ready Python snippets for learners and developers
PythonSkillset code samples are short, focused examples organised by topic and difficulty. Every snippet is server-rendered HTML — readable by search engines and easy to copy. Open any sample, read the notes, copy the code, then press Try in editor to run it in the browser with Pyodide.
How to use this library
- Pick a topic section — strings, lists, files, functions, and more
- Open a sample, read How it works, and copy the code block
- Run it in the IDE, tweak values, then take a related quiz or tutorial lesson
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.