Python Comprehensions: List, Dictionary, Set, and Tuple Examples

Python comprehensions are a concise way to construct new sequences or collections from existing iterables. The language supports list, dictionary, set, and tuple comprehensions, each following a similar pattern of an expression followed by a for clause and optional if filter.

List comprehension uses square brackets: [expression for item in iterable] or [expression for item in iterable if condition] . Example that filters strings longer than three characters and converts them to uppercase:

names = ['Bob', 'Tom', 'alice', 'Jerry', 'Wendy', 'Smith']
new_names = [name.upper() for name in names if len(name) > 3]
print(new_names)
# Output: ['ALICE', 'JERRY', 'WENDY', 'SMITH']

Another example computes all numbers less than 30 divisible by 3:

multiples = [i for i in range(30) if i % 3 == 0]
print(multiples)
# Output: [0, 3, 6, 9, 12, 15, 18, 21, 24, 27]

Dictionary comprehension uses curly braces with a key‑value expression: {key_expr: value_expr for item in collection} or with a filter. Example creating a dictionary where each string is a key and its length is the value:

listdemo = ['Google', 'Runoob', 'Taobao']
newdict = {key: len(key) for key in listdemo}
print(newdict)
# Output: {'Google': 6, 'Runoob': 6, 'Taobao': 6}

Creating a dictionary of numbers to their squares:

dic = {x: x**2 for x in (2, 4, 6)}
print(dic)
# Output: {2: 4, 4: 16, 6: 36}

Set comprehension also uses curly braces but produces a set: {expression for item in iterable} or with a filter. Example generating squares of 1, 2, and 3:

setnew = {i**2 for i in (1, 2, 3)}
print(setnew)
# Output: {1, 4, 9}

Example extracting characters from a string that are not in "abc":

a = {x for x in 'abracadabra' if x not in 'abc'}
print(a)
# Output: {'d', 'r'}

Tuple comprehension (generator expression) uses parentheses and returns a generator object: (expression for item in iterable) or with a filter. Example generating numbers 1‑9 as a generator and converting it to a tuple:

a = (x for x in range(1, 10))
print(a)  # <generator object ...>
tuple_a = tuple(a)
print(tuple_a)
# Output: (1, 2, 3, 4, 5, 6, 7, 8, 9)

These comprehension forms enable compact, readable, and efficient data processing in Python, making them essential tools for everyday programming.