Lists & loops
Iterate, transform, and combine sequences with readable loop patterns.
Convert a List of Integers to a Comma-Separated String in Python
Convert a list of integers into a single comma-separated string using a generator expression and str.join.
def ints_to_comma_string(numbers):
return ",".join(str(num) for num in numbers)
if __name__ == "__main__":
numbers = [1, 2, 3, 4, 5]
result = ints_to_comma_string(numbers)
print(result)Extract Data by Type from a List in Python: Numbers and Strings
Loop through a mixed list to filter out numeric and string values into separate lists.
def extract_numbers(items):
"""Extract all numeric values from a mixed list."""
numbers = []
for item in items:
if isinstance(item, (int, float)) and not isinstance(item, bool):
numbers.append(item)
return numbers
def extract_strings(items):
"""Extract all string values from a…Format Lists of Tuples into Numbered Lines in Python
This code loops through a list of (name, grade) tuples and formats each into a numbered line using enumerate and f-strings.
def format_students(students):
formatted = []
for i, student in enumerate(students, start=1):
name, grade = student
formatted.append(f"{i}. {name}: {grade}")
return "\n".join(formatted)
if __name__ == "__main__":
students = [
("Alice", 92),
("Bob", 85),
("Charl…Generate Data Helper for Beginners in Python
Define two functions that create a random list of integers and then compute basic summary statistics like count, total, average, maximum, and minimum using simple loops.
from random import randint
def build_dataset(size: int, max_val: int) -> list[int]:
data = []
for _ in range(size):
data.append(randint(1, max_val))
return data
def summarize(data: list[int]) -> dict[str, float]:
total = 0
maximum = data[0]
minimum = data[0]
for value in data:
…How to Build a Text Processor with Lists and Loops in Python
A beginner-friendly Python script that analyzes text by counting sentences, words, and word lengths using lists and for loops, then prints the results.
def process_text(text):
"""Simple text processor for beginners using lists and loops."""
sentences = text.replace('!', '.').replace('?', '.').split('.')
words = text.split()
word_counts = []
for sentence in sentences:
sentence_word_count = len(sentence.split())
word_counts.appe…How to Calculate the Sum of List Elements in Python
Iterates over a list with a for loop, accumulates each number into a total variable, and returns the sum of all elements.
def sum_list_elements(numbers):
"""Return the sum of all elements in a list."""
total = 0
for num in numbers:
total += num
return total
if __name__ == "__main__":
sample_list = [1, 2, 3, 4, 5]
result = sum_list_elements(sample_list)
print(f"The sum of {sample_list} is {result}")How to Compute Percentile Value from Sorted List in Python
Compute any percentile value from a sorted list using linear interpolation between ranks.
def percentile(sorted_data, percentile_value):
"""Return the value below which `percentile_value`% of data falls."""
if not sorted_data:
raise ValueError("Cannot compute percentile of empty list")
if not 0 <= percentile_value <= 100:
raise ValueError("Percentile must be between 0 and 100")
…How to Convert Data Types in Python Lists
Convert a mixed list of values to integers, floats, or strings based on their content, with graceful fallback for unparseable strings.
def convert_data(data):
"""Convert a mixed list of values to strings, ints, and floats."""
result = []
for item in data:
if isinstance(item, (int, float)):
result.append(str(item))
elif isinstance(item, str):
try:
if '.' in item:
r…How to Filter Even Numbers and Square Them in Python
Create two beginner-friendly helper functions that filter even numbers and compute squares of a number list using loops, then print the results along with the sum and average.
def get_even_numbers(numbers):
evens = []
for num in numbers:
if num % 2 == 0:
evens.append(num)
return evens
def get_squares(numbers):
squares = []
for num in numbers:
squares.append(num ** 2)
return squares
numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
even_numbers …How to Filter a List in Python with a Loop
Filter a list of numbers by a threshold using a for loop and append results to a new list, then print the filtered values and count.
ages = [34, 12, 45, 8, 67, 21, 18, 55, 3]
threshold = 18
adults = []
for age in ages:
if age >= threshold:
adults.append(age)
print("All ages:", ages)
print("Adults (18+):", adults)
print("Count of adults:", len(adults))How to Flatten a Deeply Nested List in Python Recursively
A recursive function that flattens arbitrarily deep nested lists into a single flat list using isinstance checks.
def flatten(nested_list):
if not nested_list:
return []
if isinstance(nested_list[0], list):
return flatten(nested_list[0]) + flatten(nested_list[1:])
return [nested_list[0]] + flatten(nested_list[1:])
if __name__ == "__main__":
data = [1, [2, [3, [4, [5]]]], [6, [7, [8, [9]]]], 10]
…How to Group Consecutive Equal Elements in Python
Group consecutive equal elements in a list into sublists using itertools.groupby.
from itertools import groupby
def group_consecutive(lst):
"""Group consecutive equal elements into sublists."""
return [list(group) for _, group in groupby(lst)]
if __name__ == "__main__":
input_list = [1, 1, 2, 2, 2, 3, 1, 1, 4, 4, 4, 4]
result = group_consecutive(input_list)
print("Input:", inp…How to Interleave Two Lists in Python Until One List Exhausted
Interleave elements from two lists pairwise using zip, stopping when either list runs out of items.
def interleave(a, b):
result = []
for x, y in zip(a, b):
result.extend([x, y])
return result
if __name__ == "__main__":
list1 = [1, 2, 3, 4, 5]
list2 = ["a", "b", "c"]
print(interleave(list1, list2))How to Merge Two Lists in Python
Merge two Python lists into a single combined list by appending each element with a simple loop, achieving the same result as the + operator.
def merge_lists(list_a, list_b):
merged = []
for item in list_a:
merged.append(item)
for item in list_b:
merged.append(item)
return merged
if __name__ == "__main__":
fruits = ["apple", "banana"]
vegetables = ["carrot", "spinach"]
result = merge_lists(fruits, vegetables)
…How to Merge Two Sorted Lists in Python
Merge two sorted lists into one sorted list using a two-pointer loop, then extend with remaining elements.
def merge_sorted_lists(list1, list2):
merged = []
i = j = 0
while i < len(list1) and j < len(list2):
if list1[i] <= list2[j]:
merged.append(list1[i])
i += 1
else:
merged.append(list2[j])
j += 1
merged.extend(list1[i:])
merged…How to Parse Bullet Points in Python
Extract bullet point items from raw text by splitting lines and filtering those that start with '- ' or '* '.
def parse_bullet_points(text):
"""Extract bullet point items from raw text."""
lines = text.splitlines()
items = []
for line in lines:
stripped = line.strip()
if stripped.startswith("- ") or stripped.startswith("* "):
item = stripped[2:]
if item:
…How to Parse Delimited Data into a Python List
Splits a pipe-delimited string, strips whitespace, filters empty items, and returns a clean list with a loop.
def parse_data(raw_data):
"""Parse a pipe-delimited string into a list of cleaned items."""
items = raw_data.split("|")
parsed = []
for item in items:
cleaned = item.strip()
if cleaned:
parsed.append(cleaned)
return parsed
if __name__ == "__main__":
data = " apple…How to Parse a Comma String into a List of Integers in Python
Converts a comma-separated string into a list of integers, handling spaces and empty inputs.
def parse_csv_to_ints(text: str) -> list[int]:
"""Parse a comma-separated string into a list of integers."""
if not text.strip():
return []
return [int(part.strip()) for part in text.split(",") if part.strip()]
if __name__ == "__main__":
sample = "10, 20, 30, 40, 50"
result = parse_csv_to_…How to Partition a List Around a Pivot in Python
This code splits a list into three parts—elements less than, equal to, and greater than a pivot—then concatenates them to produce a partitioned list while preserving the original order within each group.
def partition_list(lst, pivot):
less = []
equal = []
greater = []
for item in lst:
if item < pivot:
less.append(item)
elif item == pivot:
equal.append(item)
else:
greater.append(item)
return less + equal + greater
if __name__ == "__main__…How to Process Text into Words in Python
Splits a string into words, strips punctuation, and returns a list of uppercase words using a loop.
def convert_text_processor(text):
words = text.split()
processed = []
for word in words:
clean = word.strip('.,!?;:')
if len(clean) > 0:
processed.append(clean.upper())
return processed
if __name__ == "__main__":
sample_text = "Hello, world! This is a Python e…How to Process Text with Lists and Loops in Python
A beginner-friendly text processor that splits a sentence into words, filters by length, counts vowels, and reports results using lists and loops.
text = "Python makes text processing easy and fun"
words = text.lower().split()
print("Words in the sentence:")
for index, word in enumerate(words, start=1):
print(f"{index}. {word}")
filtered_words = [word for word in words if len(word) > 3]
print(f"\nWords longer than 3 characters: {filtered_words}")
letter…How to Reverse a List in Place Without Using reverse() in Python
A two-pointer while loop swaps elements from both ends toward the center to reverse a list in place without creating a copy.
def reverse_list_in_place(lst):
left = 0
right = len(lst) - 1
while left < right:
lst[left], lst[right] = lst[right], lst[left]
left += 1
right -= 1
if __name__ == "__main__":
my_list = [1, 2, 3, 4, 5]
print("Original:", my_list)
reverse_list_in_place(my_list)
prin…How to Safely Convert a List of Strings to Integers in Python
Convert a list of strings to integers while skipping invalid entries and collecting the failed values for inspection.
def safe_to_int(values):
"""Safely convert a list of strings to integers, skipping invalid entries."""
result = []
errors = []
for value in values:
try:
result.append(int(value))
except (ValueError, TypeError):
errors.append(value)
return result, errors
if …How to Split a List at the First Occurrence of a Value in Python
This function splits a list into two parts at the first occurrence of a given value, returning the left and right portions.
def split_at_first(lst, value):
try:
idx = lst.index(value)
return lst[:idx], lst[idx:]
except ValueError:
return lst, []
if __name__ == "__main__":
sample = [1, 2, 3, 4, 3, 5]
value = 3
left, right = split_at_first(sample, value)
print("Left:", left)
print("Right:"…Browse by section
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Lists & loops — Python code examples
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