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How to Convert a List to an Iterator in Python with iter()
This code converts a list into an iterator using the built-in iter() function and retrieves items sequentially with next(), handling exhaustion with StopIteration.
def main():
# Original list
fruits = ["apple", "banana", "cherry"]
# Convert the list to an iterator using iter()
fruit_iterator = iter(fruits)
# Retrieve items one at a time with next()
print(next(fruit_iterator)) # apple
print(next(fruit_iterator)) # banana
print(next(fruit_iterat…How to Create an Iterator Class with Dunder Methods in Python
A minimal Counter class implementing __iter__ and __next__ to act as a self-iterating iterator, yielding numbers from start to end-1.
class Counter:
def __init__(self, start=0, end=5):
self.current = start
self.end = end
def __iter__(self):
return self
def __next__(self):
if self.current >= self.end:
raise StopIteration
value = self.current
self.current += 1
return val…How to Use Python's next() Builtin with a Default Sentinel Value
A wrapper function that returns the next item from an iterator, or a default sentinel value when the iterator is exhausted.
def get_next_or_default(iterator, default=None):
"""Return the next item from an iterator, or default if exhausted."""
return next(iterator, default)
if __name__ == "__main__":
fruits = iter(["apple", "banana", "cherry"])
print(get_next_or_default(fruits)) # apple
print(get_next_or…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
…Game of Life Next State Grid in Python
Compute the next generation of Conway's Game of Life from a 2D grid using the standard three rules with neighbor counting.
def next_state(grid):
m, n = len(grid), len(grid[0])
new = [[0] * n for _ in range(m)]
for r in range(m):
for c in range(n):
total = 0
for dr in (-1, 0, 1):
for dc in (-1, 0, 1):
if dr == 0 and dc == 0:
continue
…How to Find the Next Greater Element for Each List Item in Python
Use a monotonic stack to find the next greater element to the right for every item in a list, in O(n) time.
def next_greater_element(nums):
result = [-1] * len(nums)
stack = []
for i in range(len(nums) - 1, -1, -1):
while stack and stack[-1] <= nums[i]:
stack.pop()
result[i] = stack[-1] if stack else -1
stack.append(nums[i])
return result
if __name__ == "__main…Pair Elements with Next Cyclic Neighbor in Python
Create tuples pairing every element with its next element, wrapping around to the first element for the last one.
def cyclic_pairs(lst):
if not lst:
return []
return [(lst[i], lst[(i + 1) % len(lst)]) for i in range(len(lst))]
if __name__ == "__main__":
sample = [1, 2, 3, 4, 5]
result = cyclic_pairs(sample)
print(result)How to Implement the Iterator Protocol in Python
A manual iterator class using __iter__ and __next__, compared with an equivalent generator using yield.
class ManualCounter:
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
value = self.current
self.current += 1
return valu…Parse cron expression and compute next run datetime in Python
Parse a 5-field cron expression and compute the next matching datetime starting from a given base time.
from datetime import datetime, timedelta
import re
def parse_cron_and_next_run(cron_expr, base_time=None):
"""Parse a cron expression and compute the next run time."""
if base_time is None:
base_time = datetime.now().replace(second=0, microsecond=0)
fields = cron_expr.split()
if len(fields) !…Bump Semantic Version Git Tag in Python
Automatically find the latest Git tag and compute the next patch release using semantic versioning (semver) in Python.
from re import match
from subprocess import run
SEMVER_PATTERN = r"^v(?P<major>0|[1-9]\d*)\.(?P<minor>0|[1-9]\d*)\.(?P<patch>0|[1-9]\d*)(?:-(?P<prerelease>[0-9A-Za-z-]+(?:\.[0-9A-Za-z-]+)*))?(?:\+(?P<buildmetadata>[0-9A-Za-z-]+(?:\.[0-9A-Za-z-]+)*))?$"
def get_latest_tag() -> str:
result = run(["git", "describe…How to Auto-Suggest a SemVer Bump From Git Commit Messages in Python
This code scans Git commit messages (recent or sample) and suggests the next Semantic Versioning bump type — major, minor, patch, or none.
import re
import subprocess
from pathlib import Path
def get_commit_messages(path="."):
"""Read commit messages from a repo or use sample messages."""
if (Path(path) / ".git").exists():
out = subprocess.run(
["git", "-C", path, "log", "--pretty=%s"], capture_output=True, text=True
…How to Add HATEOAS Links to a Python API Response
Build a Python API resource class that adds self and next HATEOAS links to JSON responses, with a mock example for pagination.
import json
class Resource:
def __init__(self, name, data, next_page=None):
self.links = {"self": f"/api/resources/{name}"}
if next_page is not None:
self.links["next"] = f"/api/resources?page={next_page}"
self.data = data
def to_dict(self):
return {"links": self.…How to Build Cursor Pagination with Next and Prev Tokens in Python
A minimal cursor pagination implementation that returns next and previous cursor tokens for navigating a dataset.
from pprint import pprint
def make_cursor(page):
return f"page:{page:04d}"
def parse_cursor(cursor):
_, page = cursor.split(":", 1)
return int(page)
def paginate(all_items, page_size, cursor=None):
start = parse_cursor(cursor) if cursor else 0
end = start + page_size
items = all_items[sta…How to Mock Cron Schedule in Python
Compute the next scheduled run time for a cron expression using a pure-Python mock parser.
import re
from datetime import datetime, timedelta
class CronMock:
def __init__(self, expression):
self.expression = expression
self.minutes = self._parse_field(expression.split()[0], 0, 59)
self.hours = self._parse_field(expression.split()[1], 0, 23)
self.days = self._parse_field(…How to Simulate a Stable Sort Cursor in Python
Build a MongoDB-style cursor mock that stably sorts records by a key while preserving original order for ties, with next() and rewind() methods.
```python
import random
class CursorStableSortMock:
"""Simulates stable sorting with a cursor-like pointer for MongoDB-style queries."""
def __init__(self, data, sort_key, reverse=False):
self.data = list(data)
self.sort_key = sort_key
self.reverse = reverse
self._index = …How to Mock a TLS Certificate Rotation Schedule in Python
Simulate a TLS certificate rotation schedule with a Python class that tracks last and next rotation dates and decides when to rotate.
import datetime
import random
import time
class CertRotator:
def __init__(self, cert_name, rotation_days=30):
self.cert_name = cert_name
self.rotation_days = rotation_days
self.last_rotated = datetime.date.today() - datetime.timedelta(days=random.randint(10, 25))
self.next_rotatio…Browse by section
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