Python: Data Types

x: int = 42
y: float = 3.14
z: complex = 2 + 3j
b: bool = True

# int supports arbitrary precision
big = 10 ** 100

# Numeric literals
hex_val = 0xFF       # 255
bin_val = 0b1010     # 10
oct_val = 0o17       # 15
sep_val = 1_000_000  # underscores for readability

s = "hello"
s = 'hello'
s = """multi
line"""

len(s)          # 5
s[0]            # 'h'
s[-1]           # 'o'
s[1:3]          # 'el'
s.upper()       # 'HELLO'

fruits = ["apple", "banana", "cherry"]
mixed = [1, "hello", 3.14, True]

fruits.append("date")
fruits.insert(1, "avocado")
fruits.remove("banana")
fruits.pop()           # removes and returns last
fruits.pop(0)          # removes and returns at index
fruits.sort()
fruits.reverse()
len(fruits)
fruits[0]
fruits[-1]
fruits[1:3]

point = (1, 2)
single = (42,)           # single-element tuple needs trailing comma
empty = ()

x, y = point             # unpacking
a, *rest = (1, 2, 3, 4)  # starred unpacking: a=1, rest=[2,3,4]

range(5)        # 0..4
range(2, 8)     # 2..7
range(0, 10, 2) # 0, 2, 4, 6, 8 (step)
list(range(5))  # [0, 1, 2, 3, 4]

person = {"name": "Alice", "age": 27}
person["city"] = "Vienna"
person.get("age")             # 27
person.get("email", "n/a")   # "n/a" (default if missing)
person.keys()
person.values()
person.items()               # dict_view of (key, value) pairs
"name" in person             # True
del person["city"]
person.pop("age")            # removes and returns value
person.update({"x": 1, "y": 2})

s = {1, 2, 3, 4}
s.add(5)
s.remove(3)        # raises KeyError if not found
s.discard(99)      # safe, no error if not found

a = {1, 2, 3}
b = {2, 3, 4}
a | b              # union: {1, 2, 3, 4}
a & b              # intersection: {2, 3}
a - b              # difference: {1}
a ^ b              # symmetric difference: {1, 4}
a.issubset(b)
a.issuperset(b)

fs = frozenset({1, 2, 3})

True and False   # False
True or False    # True
not True         # False

# Falsy values: False, None, 0, 0.0, "", [], {}, set(), ()
bool(0)    # False
bool("")   # False
bool([])   # False
bool(1)    # True
bool("x")  # True

b = b"hello"            # bytes: immutable sequence of bytes
ba = bytearray(b"hi")   # bytearray: mutable sequence of bytes
ba[0] = 65              # mutate in place
mv = memoryview(b)      # zero-copy view into bytes-like object

x = None
x is None      # True (use `is`, not ==)

type(42)          # <class 'int'>
isinstance(42, int)        # True
isinstance(42, (int, float))  # True (checks multiple types)

# Conversions
int("42")         # 42
int(3.9)          # 3 (truncates)
float("3.14")     # 3.14
str(42)           # "42"
bool(0)           # False
list((1, 2, 3))   # [1, 2, 3]
tuple([1, 2, 3])  # (1, 2, 3)
set([1, 2, 2, 3]) # {1, 2, 3}
dict([("a", 1)])  # {"a": 1}