Tuples & Sets

# Creating tuples
empty = ()
single = (42,)          # Note the trailing comma!
coordinates = (10, 20)
mixed = (1, "hello", 3.14)

# Parentheses are optional in many contexts
point = 10, 20
print(type(point))      # <class 'tuple'>

# From other iterables
tuple([1, 2, 3])       # (1, 2, 3)
tuple("abc")            # ('a', 'b', 'c')

point = (3, 4)

# Indexing and slicing — same as lists
point[0]     # 3
point[-1]    # 4

# point[0] = 5  # TypeError! Tuples are immutable

# Concatenation and repetition
(1, 2) + (3, 4)     # (1, 2, 3, 4)
(1,) * 3            # (1, 1, 1)

# Membership
3 in (1, 2, 3)      # True

# Unpacking
x, y = (10, 20)     # x=10, y=20
x, y = y, x         # Swap — works because tuple on RHS

# Fixed data that shouldn't change
DAYS = ("Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun")

# Function returning multiple values
def min_max(items):
    return min(items), max(items)

low, high = min_max([3, 1, 4, 1, 5])
print(low, high)  # 1 5

# Dictionary keys (lists can't be keys)
locations = {
    (40.7128, -74.0060): "New York",
    (51.5074, -0.1278): "London",
}

# Named tuples for lightweight objects
from collections import namedtuple
Point = namedtuple("Point", ["x", "y"])
p = Point(3, 4)
print(p.x, p.y)     # 3 4
print(p[0], p[1])   # 3 4 — also supports indexing

# Creating sets
empty = set()            # {} creates an empty dict, not set!
numbers = {1, 2, 3, 4, 5}
mixed = {1, "hello", 3.14}

# From other iterables — duplicates are removed
set([1, 2, 2, 3, 3, 3])  # {1, 2, 3}
set("mississippi")        # {'m', 'i', 's', 'p'}

a = {1, 2, 3, 4}
b = {3, 4, 5, 6}

# Union
a | b              # {1, 2, 3, 4, 5, 6}
a.union(b)

# Intersection
a & b              # {3, 4}
a.intersection(b)

# Difference
a - b              # {1, 2} — in a but not b
b - a              # {5, 6} — in b but not a

# Symmetric difference
a ^ b              # {1, 2, 5, 6} — in either but not both

# Subset/superset
{1, 2}.issubset(a)      # True
a.issuperset({1, 2})    # True

items = {1, 2, 3}

# Adding and removing
items.add(4)             # {1, 2, 3, 4}
items.add(2)             # No effect — 2 already exists
items.remove(3)          # Removes 3 — KeyError if not found
items.discard(10)        # Removes if exists, no error if not
popped = items.pop()     # Removes and returns arbitrary element
items.clear()            # Empty the set

# Set comprehensions
squares = {x ** 2 for x in range(10)}
# {0, 1, 4, 9, 16, 25, 36, 49, 64, 81}

fs = frozenset([1, 2, 3])
# fs.add(4)  # AttributeError!
# Can be used as dictionary key
data = {frozenset({1, 2}): "pair"}

# Remove duplicates from a list
items = [1, 2, 2, 3, 3, 3]
unique = list(set(items))  # [1, 2, 3] — order may vary