Syntax and Builtins

Core language syntax and builtins you reach for in everyday Python. Results appear in the same fence: same-line # comments when short, multiline # blocks below the sample when not.

f-string Formatting

Interpolate expressions with f-strings - the preferred string formatting style.

name = "Ada"
print(f"Hello, {name}!")   # Hello, Ada!
print(f"{3.14159:.2f}")    # 3.14

Unpacking Assignment

Unpack iterables into names; use * to capture the rest.

a, b, *rest = [1, 2, 3, 4]  # a=1, b=2, rest=[3, 4]
first, last = ("x", "y")     # first='x', last='y'

Walrus Operator

Assign inside an expression with := when it improves clarity (filters, while loops).

s = "hello"
if (n := len(s)) > 3:        # n=5
    print(n)                 # 5

enumerate zip

Pair indexes with items via enumerate; walk multiple iterables with zip.

list(enumerate(["a", "b"], start=1))  # [(1, 'a'), (2, 'b')]
list(zip([1, 2], ["x", "y"]))         # [(1, 'x'), (2, 'y')]

any all

Short-circuit checks over iterables for existence or universal predicates.

all(x > 0 for x in [1, 2, 3])   # True
any(x < 0 for x in [1, -1, 2])  # True
any(x < 0 for x in [1, 2, 3])   # False

Truthy Falsy

Empty containers, 0, None, and "" are falsy - use explicitly when needed.

bool([])          # False
bool([0])         # True
None or "fallback"  # 'fallback'

match Statement

Structural pattern matching for tagged data (3.10+).

command = {"op": "add", "n": 3}
match command:
    case {"op": "add", "n": int(n)}:
        total = 10 + n       # total=13
    case _:
        raise ValueError(command)

slice Steps

Slices support start:stop:step - including reverse with [::-1].

nums = [0, 1, 2, 3, 4]
nums[::2]    # [0, 2, 4]
nums[::-1]   # [4, 3, 2, 1, 0]

sorted key

Sort with a key function; use reverse=True when needed.

users = [{"n": "b", "s": 1}, {"n": "a", "s": 3}]
sorted(users, key=lambda u: u["s"], reverse=True)
# [
#   {'n': 'a', 's': 3},
#   {'n': 'b', 's': 1},
# ]

min max default

min/max accept default when the iterable may be empty (3.4+).

max([3, 9, 2], default=0)   # 9
max([], default=0)          # 0
min([3, 9, 2], default=0)   # 2

round and divmod

Numeric helpers for currency-ish rounding awareness and quotient/remainder.

divmod(20, 3)     # (6, 2)
round(1.25, 1)    # 1.2
round(2.5)        # 2  (banker's rounding to even)

isinstance check

Prefer isinstance over comparing type(x) is for polymorphism.

isinstance(3, (int, float))     # True
isinstance(True, int)           # True  (bool subclasses int)
isinstance("3", (int, float))   # False

callable map filter

Functional helpers exist - comprehensions are often clearer.

nums = [1, 2, 3, 4]
[n * n for n in nums if n % 2 == 0]  # [4, 16]

chr ord

Convert between code points and characters.

ord("A")   # 65
chr(65)    # 'A'
ord("€")   # 8364

help and dir

REPL discovery tools for exploring objects and modules.

"upper" in dir(str)   # True
# help(list.append)   # opens docs in the REPL

Collections and Structures - list dict set patterns
Functions and Scope - def and lambda
Typing and Annotations - type the builtins

Stack versions: Python 3.14.0 (stable 3.14, maintenance 3.13) · uv 0.6+ · ruff 0.9+

f-string Formatting

Interpolate expressions with f-strings - the preferred string formatting style.

name = "Ada"
print(f"Hello, {name}!")   # Hello, Ada!
print(f"{3.14159:.2f}")    # 3.14

Unpacking Assignment

Unpack iterables into names; use * to capture the rest.

a, b, *rest = [1, 2, 3, 4]  # a=1, b=2, rest=[3, 4]
first, last = ("x", "y")     # first='x', last='y'

Walrus Operator

Assign inside an expression with := when it improves clarity (filters, while loops).

s = "hello"
if (n := len(s)) > 3:        # n=5
    print(n)                 # 5

enumerate zip

Pair indexes with items via enumerate; walk multiple iterables with zip.

list(enumerate(["a", "b"], start=1))  # [(1, 'a'), (2, 'b')]
list(zip([1, 2], ["x", "y"]))         # [(1, 'x'), (2, 'y')]

any all

Short-circuit checks over iterables for existence or universal predicates.

all(x > 0 for x in [1, 2, 3])   # True
any(x < 0 for x in [1, -1, 2])  # True
any(x < 0 for x in [1, 2, 3])   # False

Truthy Falsy

Empty containers, 0, None, and "" are falsy - use explicitly when needed.

bool([])          # False
bool([0])         # True
None or "fallback"  # 'fallback'

match Statement

Structural pattern matching for tagged data (3.10+).

command = {"op": "add", "n": 3}
match command:
    case {"op": "add", "n": int(n)}:
        total = 10 + n       # total=13
    case _:
        raise ValueError(command)

slice Steps

Slices support start:stop:step - including reverse with [::-1].

nums = [0, 1, 2, 3, 4]
nums[::2]    # [0, 2, 4]
nums[::-1]   # [4, 3, 2, 1, 0]

sorted key

Sort with a key function; use reverse=True when needed.

users = [{"n": "b", "s": 1}, {"n": "a", "s": 3}]
sorted(users, key=lambda u: u["s"], reverse=True)
# [
#   {'n': 'a', 's': 3},
#   {'n': 'b', 's': 1},
# ]

min max default

min/max accept default when the iterable may be empty (3.4+).

max([3, 9, 2], default=0)   # 9
max([], default=0)          # 0
min([3, 9, 2], default=0)   # 2

round and divmod

Numeric helpers for currency-ish rounding awareness and quotient/remainder.

divmod(20, 3)     # (6, 2)
round(1.25, 1)    # 1.2
round(2.5)        # 2  (banker's rounding to even)

isinstance check

Prefer isinstance over comparing type(x) is for polymorphism.

isinstance(3, (int, float))     # True
isinstance(True, int)           # True  (bool subclasses int)
isinstance("3", (int, float))   # False

callable map filter

Functional helpers exist - comprehensions are often clearer.

nums = [1, 2, 3, 4]
[n * n for n in nums if n % 2 == 0]  # [4, 16]

chr ord

Convert between code points and characters.

ord("A")   # 65
chr(65)    # 'A'
ord("€")   # 8364

help and dir

REPL discovery tools for exploring objects and modules.

"upper" in dir(str)   # True
# help(list.append)   # opens docs in the REPL

Collections and Structures - list dict set patterns
Functions and Scope - def and lambda
Typing and Annotations - type the builtins

Stack versions: Python 3.14.0 (stable 3.14, maintenance 3.13) · uv 0.6+ · ruff 0.9+

Syntax and Builtins

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Syntax and Builtins