map() / filter() / sorted()

# Applies a function to each element of an iterable and returns the results.
map(function, iterable, ...)

# Returns only the elements for which the function returns True.
filter(function, iterable)

# Returns a new sorted list (the original iterable is not modified).
sorted(iterable, key=None, reverse=False)

# Returns the minimum value, maximum value, or sum of an iterable.
min(iterable, key=None)
max(iterable, key=None)
sum(iterable, start=0)

sample_map_filter_sorted.py

# Use map() to transform each element.
numbers = [1, 2, 3, 4, 5]
doubled = list(map(lambda x: x * 2, numbers))
print(doubled)  # [2, 4, 6, 8, 10]

# Convert a list of strings to integers.
str_nums = ["10", "20", "30"]
int_nums = list(map(int, str_nums))
print(int_nums)  # [10, 20, 30]

# Use filter() to keep only elements that match a condition.
evens = list(filter(lambda x: x % 2 == 0, numbers))
print(evens)  # [2, 4]

# Passing None removes all falsy values.
data = [1, 0, "hello", "", None, [], [1, 2]]
clean = list(filter(None, data))
print(clean)  # [1, 'hello', [1, 2]]

# Use sorted() to create a new sorted list.
fighters = ["Vegeta", "Krillin", "Son Goku", "Bulma"]
sorted_fighters = sorted(fighters)
print(sorted_fighters)  # Sorted in alphabetical order.

# Sort by string length using a key function.
sorted_by_len = sorted(fighters, key=len)
print(sorted_by_len)  # Sorted from shortest to longest string.

# Sort a list of dictionaries by a specific key.
students = [
    {"name": "Son Goku", "score": 92},
    {"name": "Vegeta", "score": 85},
    {"name": "Krillin", "score": 78},
]
by_score = sorted(students, key=lambda s: s["score"], reverse=True)
print(by_score[0]["name"])  # Son Goku (highest score)

# Using min(), max(), and sum().
scores = [85, 92, 78, 95, 70]
print(min(scores))   # 70
print(max(scores))   # 95
print(sum(scores))   # 420
print(sum(scores) / len(scores))  # 84.0 (average)

# Use a key function to find the dictionary with the highest score.
best = max(students, key=lambda s: s["score"])
print(best["name"])  # Son Goku

python3 map_filter_sorted.py
[2, 4, 6, 8, 10]
[10, 20, 30]
[2, 4]
[1, 'hello', [1, 2]]
['Bulma', 'Krillin', 'Son Goku', 'Vegeta']
['Bulma', 'Vegeta', 'Krillin', 'Son Goku']
Son Goku
70
95
420
84.0
Son Goku

Both map() and filter() return lazy iterators. If you need the results as a list, always wrap them with list(). Without the conversion, you will see an object representation like <map object at 0x...> instead of the actual values.

In modern Python, list comprehensions are generally preferred over map() and filter() for readability. For example, list(map(lambda x: x*2, nums)) can be written as [x*2 for x in nums]. That said, map() is more concise when passing an existing function such as int or str.

Unlike the sort() method on lists, sorted() does not modify the original object — it always returns a new list. It also works with any iterable, including strings, tuples, and dictionary keys.