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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:"…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}")Add Type Hints to Function Parameters and Return in Python
Add type hints to function parameters and return values in Python for clearer, more maintainable code using the typing module.
from typing import List, Optional, Dict
def average(numbers: List[float]) -> float:
return sum(numbers) / len(numbers)
def full_name(first: str, last: Optional[str] = "") -> str:
return f"{first} {last}".strip()
def build_user(name: str, age: int, email: Optional[str] = None) -> Dict[str, object]:
us…How to Build a Simple Decorator That Logs Function Calls in Python
This code shows how to create a reusable decorator that logs each function call, including arguments, return value, and execution time.
import functools
import time
def log_calls(func):
@functools.wraps(func)
def wrapper(*args, **kwargs):
print(f"Calling {func.__name__} with args={args}, kwargs={kwargs}")
start = time.time()
result = func(*args, **kwargs)
end = time.time()
print(f"{func.__name__} return…How to Count Items with Default Parameters in Python
Define a Python function that prints each item with a running counter, using default parameters to allow custom start values and step increments.
def count_items(items, start=0, step=1):
"""Count items in a list with configurable start value and step."""
count = start
for item in items:
print(f"{count}: {item}")
count += step
if __name__ == "__main__":
fruits = ["apple", "banana", "cherry"]
print("Default parameters (start=0…How to Create a Higher-Order Function in Python (Apply Twice)
This code defines a higher-order function that takes another function and a value, then applies the function twice to the value and returns the result.
def apply_twice(func, value):
return func(func(value))
def add_ten(x):
return x + 10
def square(x):
return x ** 2
if __name__ == "__main__":
print(apply_twice(add_ten, 5))
print(apply_twice(square, 3))How to Define a Function with Default Parameter Values in Python
This code demonstrates defining a Python function with default parameter values, showing how to call it with zero, one, or two arguments.
def greet(name: str = "World", punctuation: str = "!") -> str:
"""Return a greeting message using default parameter values."""
message = f"Hello, {name}{punctuation}"
return message
if __name__ == "__main__":
# Call with no arguments – uses both defaults
print(greet())
# Call with one argume…How to Document Python Functions with Google Style Docstrings
Document a Python function with a Google style docstring to describe arguments and return values clearly.
def calculate_rectangle_area(length: float, width: float) -> float:
"""Calculate the area of a rectangle.
Args:
length (float): The length of the rectangle in meters.
width (float): The width of the rectangle in meters.
Returns:
float: The area of the rectangle in square meters.
…How to Load a .env File Manually in Python
Parse a .env-style key-value file into a Python dictionary using only the standard library, with comment and quoted-value handling.
import re
from pathlib import Path
def load_dotenv_file(filepath: str) -> dict[str, str]:
"""Parse a .env-style file into a dictionary."""
env = {}
path = Path(filepath)
if not path.exists():
raise FileNotFoundError(f"Environment file not found: {filepath}")
for line in path.read_text()…How to Parse Function Parameters with Defaults in Python
Create Python functions with default parameter values to make arguments optional and provide sensible fallbacks.
def greet(name, greeting="Hello", punctuation="!"):
"""Greet a person with customizable greeting and punctuation."""
return f"{greeting}, {name}{punctuation}"
def describe_fruit(fruit, color="unknown", ripe=False):
"""Describe a fruit with optional attributes."""
status = "ripe" if ripe else "not ripe…How to Pipe Data Through a List of Transform Functions in Python
Applies a sequence of functions to an initial value using functools.reduce, creating a reusable pipe utility.
from functools import reduce
def pipe(data, *transforms):
return reduce(lambda value, func: func(value), transforms, data)
def double(x):
return x * 2
def add_one(x):
return x + 1
def to_string(x):
return f"Result: {x}"
if __name__ == "__main__":
initial = 5
result = pipe(initial, double, …How to Read Environment Variables in Python with Default Values
Retrieve an environment variable safely using os.getenv() with a fallback default when the variable is missing.
import os
database_url = os.getenv("DATABASE_URL", "postgresql://localhost:5432/mydb")
print(f"Database URL: {database_url}")How to Return Multiple Values from a Python Function
This code demonstrates how a Python function can return multiple values as a tuple, and how to unpack that tuple into individual variables.
def get_user_stats(name, score, level):
"""Return multiple values as a tuple."""
return name, score, level
if __name__ == "__main__":
result = get_user_stats("Alice", 95, 3)
print(result)
print(type(result))
# Unpacking into individual variables
player_name, player_score, player_level…How to Use Default Parameter Values in Python Functions
Shows how to define and call Python functions with default parameter values, including overriding some or all defaults and using keyword arguments.
def greet(name, greeting="Hello", punctuation="!"):
"""Return a greeting message using default parameters."""
return f"{greeting}, {name}{punctuation}"
if __name__ == "__main__":
# Using defaults
print(greet("Alice"))
# Overriding first default
print(greet("Bob", "Hi"))
# Overrid…How to Use Default Parameter Values in Python Functions
This code demonstrates how to define a Python function with default parameters and call it with varying numbers of arguments to see the defaults applied.
def greet(name, greeting="Hello", punctuation="!"):
message = f"{greeting}, {name}{punctuation}"
print(message)
if __name__ == "__main__":
greet("Alice")
greet("Bob", "Hi")
greet("Charlie", "Hey", "?")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 Validate Function Arguments in Python
Shows how to manually check argument types and values in a Python function, raising clear TypeError and ValueError messages.
def calculate_area(length: float, width: float) -> float:
"""Calculate the area of a rectangle with manual type validation."""
if not isinstance(length, (int, float)) or isinstance(length, bool):
raise TypeError(f"length must be a number, got {type(length).__name__}")
if not isinstance(width, (int,…How to use function defaults in Python
Define Python functions with default parameter values so callers can omit arguments and use sensible fallbacks.
def greet(name="Guest", greeting="Hello", punctuation="!"):
"""Return a greeting message using default parameters."""
return f"{greeting}, {name}{punctuation}"
def describe_pet(pet_name, animal_type="dog"):
"""Display information about a pet with a default animal type."""
print(f"I have a {animal_type…Python Function Default Parameters Explained with Examples
Learn how to define Python functions with default parameter values and call them with fewer arguments than declared.
def greet(name, greeting="Hello", punctuation="!"):
return f"{greeting}, {name}{punctuation}"
def calculate_area(length, width=1, unit="sq units"):
area = length * width
return f"Area: {area} {unit}"
if __name__ == "__main__":
print(greet("Alice"))
print(greet("Bob", "Hi"))
print(greet("Charl…Compound interest calculator in Python
Compute future investment value with the compound interest formula and a readable year-by-year loop.
def future_value(
principal: float,
annual_rate: float,
years: int,
compounds_per_year: int = 12,
) -> float:
"""Return balance after compound interest (rounded to cents)."""
rate_per_period = annual_rate / compounds_per_year
periods = compounds_per_year * years
amount = principal * (1 …Catch ValueError and print friendly message in Python
Wrap an int() call in a try/except block and print a friendly message when ValueError is raised.
try:
number = int("not_a_number")
except ValueError:
print("That's not a valid number. Please enter digits only.")Handle ValueError and ZeroDivisionError in Python with try except
Learn how to catch ValueError and ZeroDivisionError in Python with a practical safe_divide function and demonstrate error handling for invalid conversions.
def safe_divide(numerator, denominator):
try:
result = numerator / denominator
except ValueError as e:
print(f"ValueError caught: {e}")
return None
except ZeroDivisionError:
print("Cannot divide by zero!")
return None
return result
# Test cases
print(safe_divide…How to Catch KeyError with a Default Value in Python Dictionaries
Safely retrieve dictionary values while catching KeyError and handling None values by returning a default.
def get_value(data, key, default=None):
"""
Safely get a value from a dictionary, returning a default if the key
is missing or the value is None.
"""
try:
value = data[key]
return value if value is not None else default
except KeyError:
return default
if __name__ == "_…Browse by section
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