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How to Split Lines and Strip Blank Lines in Python
Split a multiline string into non-empty lines and strip surrounding whitespace using a list comprehension.
import sys
def split_and_strip(text):
"""Split text into non-blank lines, stripping whitespace."""
return [line.strip() for line in text.splitlines() if line.strip()]
if __name__ == "__main__":
sample_text = """ First line
Second line
Third line """
result = split_and_strip(…How to Split Strings in Python (Beginner-Friendly)
Split Python strings by a delimiter into lists, plus a cleanup variant that strips whitespace and filters empty parts.
def split_text(text, delimiter=" "):
"""Split a string by a delimiter and return a list of parts."""
return text.split(delimiter)
def split_text_with_cleanup(text, delimiter=" "):
"""Split a string, stripping whitespace and filtering empty parts."""
parts = text.split(delimiter)
cleaned = [part.s…How to Split a String by Comma in Python
Splits a comma-separated string into a list of trimmed items using Python's built-in split and a list comprehension.
def split_csv(line):
return [item.strip() for item in line.split(",")]
if __name__ == "__main__":
sample = "apple, banana, cherry, date"
result = split_csv(sample)
print(result)
print(f"Number of items: {len(result)}")How to Filter Empty Strings in Python
Remove empty and whitespace-only strings from a list using a list comprehension with the strip() method.
def filter_empty_strings(strings):
"""
Filter out empty strings (including whitespace-only strings)
from a list of strings.
"""
return [s for s in strings if s.strip()]
if __name__ == "__main__":
sample_list = ["hello", "", "world", " ", "python", " ", "!"]
filtered = filter_empty_strin…How to Filter None Values from a Mixed List in Python
Filter None values from a mixed Python list using a list comprehension with the `is not None` condition.
mixed_list = [1, None, "hello", None, 3.14, None, [1, 2], None]
filtered_list = [item for item in mixed_list if item is not None]
print(f"Original list: {mixed_list}")
print(f"Filtered list: {filtered_list}")
print(f"Original length: {len(mixed_list)}, Filtered length: {len(filtered_list)}")How to Flatten One Level of a Nested List in Python
Flattens exactly one level of a nested list by extending the output with each inner list and appending non-list items.
def flatten_one_level(nested_list):
"""Flatten one level of a nested list."""
flattened = []
for item in nested_list:
if isinstance(item, list):
flattened.extend(item)
else:
flattened.append(item)
return flattened
if __name__ == "__main__":
# Example with mi…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 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 Split a List into Chunks in Python
Split a list into fixed-size sublists using a simple list comprehension with slicing.
def chunk_list(lst, size):
"""Split a list into sublists of given size."""
return [lst[i:i + size] for i in range(0, len(lst), size)]
if __name__ == "__main__":
sample = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
print(chunk_list(sample, 3))Pairwise Adjacent Differences in a Python List
Computes the absolute differences between each pair of adjacent elements in a list using a concise list comprehension.
def adjacent_differences(nums):
"""Return list of absolute differences between adjacent elements."""
return [abs(nums[i] - nums[i + 1]) for i in range(len(nums) - 1)]
if __name__ == "__main__":
sample = [3, 7, 2, 9, 5]
diffs = adjacent_differences(sample)
print("Original list:", sample)
print…Replace Negative Values in a List with Python
This code defines a function that replaces every negative number in a list with a replacement value, defaulting to zero, using a list comprehension.
def replace_if_negative(values, replacement=0):
return [replacement if value < 0 else value for value in values]
if __name__ == "__main__":
numbers = [5, -3, 8, -1, 0, -7, 2]
result = replace_if_negative(numbers)
print(f"Original: {numbers}")
print(f"Replaced: {result}")Benchmark list append vs comprehension in Python
This micro-benchmark compares the speed of building a list with a for loop and append versus a list comprehension, using the timeit module to get precise timings.
import timeit
# Build a list of the first 1,000,000 integers using append in a loop
def append_loop(n=1_000_000):
result = []
for i in range(n):
result.append(i)
return result
# Build the same list using a list comprehension
def comprehension(n=1_000_000):
return [i for i in range(n)]
if __n…Python Filter Function with Default Parameters for Beginners
Create a reusable filter function with default parameters to keep or exclude numbers above or below a threshold.
def filter_numbers(numbers, threshold=0, reverse=False):
"""Return numbers that pass the threshold filter.
Args:
numbers: list of numbers to filter
threshold: minimum value to keep (default 0)
reverse: if True, keep numbers below threshold (default False)
"""
if reverse:
…Filter Dictionary Keys by Prefix in Python
Use a dict comprehension to build a new dictionary containing only keys that start with a given prefix.
def filter_dict_keys(data, prefix="temp_"):
"""
Filter a dictionary by keeping only keys that start with a given prefix.
Uses a dict comprehension to build a new dictionary.
"""
if not isinstance(data, dict):
raise ValueError("data must be a dictionary")
return {key: value for key, valu…How to Build a Gradebook with Python Dictionaries and Sets
Create a gradebook dictionary from student names and grades, find top students with a set comprehension, and add extra credit with a dict comprehension.
def build_gradebook(students, grades):
"""Create a dictionary mapping student names to their grades."""
return dict(zip(students, grades))
def find_top_students(gradebook, passing_grade=60):
"""Return a set of students with grades at or above the passing grade."""
return {name for name, grade in grad…How to Extract Data by Category in Python with Dictionaries and Sets
Use set comprehensions and a defaultdict to extract product names by category and compute total prices per category from a list of dictionaries.
from collections import defaultdict
# Sample data: products with categories and prices
product_data = [
{"name": "Apple", "category": "fruit", "price": 0.50},
{"name": "Banana", "category": "fruit", "price": 0.30},
{"name": "Carrot", "category": "vegetable", "price": 0.80},
{"name": "Bread", "category…How to Filter a Dictionary by Predicate on Values in Python
This code defines a reusable function that builds a new dictionary containing only the items whose values satisfy a given predicate function.
def filter_dict_by_predicate(d, predicate):
"""Return a new dict with only items whose value passes the predicate."""
return {k: v for k, v in d.items() if predicate(v)}
if __name__ == "__main__":
scores = {"Alice": 85, "Bob": 42, "Charlie": 91, "Diana": 60}
# Keep only values greater than or equal t…How to Map Dictionary Values with a Transformation Function in Python
Create a reusable function that applies a transformation to every value in a dictionary and returns a new dict.
def transform_dict_values(d, func):
"""Apply a transformation function to every value in a dictionary."""
return {key: func(value) for key, value in d.items()}
if __name__ == "__main__":
original = {"a": 1, "b": 2, "c": 3}
doubled = transform_dict_values(original, lambda x: x * 2)
print(doubled)
…How to Normalize Data in Python with Dictionaries and Sets
Normalize a list of dicts by keeping selected keys, stripping/lowercasing strings, and extracting unique sorted values using set comprehension.
def normalize_data(data, keys):
"""
Normalize a list of dictionaries by keeping only specified keys
and converting values to proper types.
"""
normalized = []
for item in data:
clean_item = {}
for key in keys:
value = item.get(key)
if isinstance(value, st…How to Validate Required Dict Keys in Python
Check whether a dictionary contains all required keys and return the list of missing ones using a simple list comprehension.
def find_missing_keys(data: dict, required_keys: list) -> list:
"""Return a list of required keys that are missing from the dictionary."""
return [key for key in required_keys if key not in data]
if __name__ == "__main__":
user_data = {
"name": "Alice",
"email": "alice@example.com",
…How to swap dict keys and values in Python when values are unique
Swap dict keys and values using a dict comprehension, with a guard that raises an error when values repeat.
def swap_dict_keys_values(d):
"""Swap keys and values in a dict, assuming values are unique."""
if len(set(d.values())) != len(d.values()):
raise ValueError("Values must be unique to swap keys and values")
return {v: k for k, v in d.items()}
if __name__ == "__main__":
original = {"a": 1, "b": …Filter List to Keep Only Whitelist Values in Python
Filter a list of values to keep only those present in a predefined whitelist set using a list comprehension.
def filter_whitelist(values, whitelist):
"""Return only values that are present in the whitelist set."""
return [value for value in values if value in whitelist]
if __name__ == "__main__":
raw_values = ["apple", "banana", "cherry", "date", "apple", "elderberry"]
allowed = {"apple", "banana", "date"}
…Find All Indices of a Target Value in a Python List
Returns a list of all indices where a given target value appears in a Python list using a list comprehension with enumerate.
def find_all_indices(arr, target):
return [i for i, value in enumerate(arr) if value == target]
if __name__ == "__main__":
sample_list = [4, 2, 7, 2, 9, 2, 1, 2]
target = 2
result = find_all_indices(sample_list, target)
print(result)How to Add Two Lists Elementwise in Python
Add two equal-length lists element by element using a list comprehension with zip, returning a new list of summed values.
def elementwise_add(list1, list2):
return [a + b for a, b in zip(list1, list2)]
if __name__ == "__main__":
list_a = [1, 2, 3, 4]
list_b = [10, 20, 30, 40]
result = elementwise_add(list_a, list_b)
print(result)Browse by section
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