Sector file // python

PYTHONDECODED.

Q: What are common useful string methods?

Strings offer `split`/`join` (the idiomatic way to build strings), `strip`, `replace`, `startswith`/`endswith`, `find`, `format`, and case methods. Strings are immutable, so these return new strings.

Q: What is the difference between '==' and 'is'?

**`==`** checks value equality (calls `__eq__`); **`is`** checks identity (same object in memory). Use `==` to compare values and `is` only for singletons like `None` (`x is None`). Small ints and interned strings may share identity, which can mislead.

Q: What are mutable and immutable types in Python?

**Immutable** types (int, float, str, tuple, frozenset) can't be changed after creation — operations return new objects. **Mutable** types (list, dict, set) can be modified in place. This affects function arguments (mutable defaults are shared) and dict-key eligibility (only hashable/immutable).

Q: Why use virtual environments?

A **virtual environment** (`python -m venv`) isolates a project's dependencies and Python version from the system and other projects, preventing version conflicts. Combined with a `requirements.txt`/lock file it makes installs reproducible.

Q: How does slicing with start:stop:step work?

seq[start:stop:step] returns a new sequence from start up to (not including) stop, taking every step-th item; negative indices count from the end.

Q: How does iterable unpacking work?

Assign multiple targets at once: `a, b = 1, 2`. The starred target captures the rest: `first, *middle, last = items`. It also powers swapping (`a, b = b, a`) and unpacking in function calls (`f(*args, **kwargs)`).

Q: How are Python dictionaries implemented and ordered?

Dicts are **hash tables** giving average O(1) lookup/insert. Since Python 3.7 they **preserve insertion order** as a language guarantee. Keys must be hashable (immutable). They're the backbone of objects, namespaces, and kwargs.

Q: How do you read TOML with tomllib in Python 3.11+?

`tomllib` (3.11, PEP 680) parses TOML from binary files via `tomllib.load(f)`; it is read-only — write with `tomli-w` if needed. tomllib:

Q: What is uv and why is it replacing pip/poetry in 2025-26?

`uv` is Astral's Rust-based drop-in for pip/pip-tools/virtualenv/poetry; it resolves and installs 10-100x faster with a global cache and `uv.lock`. <text x="160" y="65" text-anchor="middle" fill="white" font-family="monospace" font

Q: How do pyproject.toml, tomllib, and uv/pyproject workflows fit together?

`pyproject.toml` (PEP 621) is the single project file; `tomllib` reads it stdlib, `uv`/`pip` consume `[project]` and `[tool.*]` tables. p

Idioms, data & internals

120 Questions74.2k Views4.5k Upvotes

22 easy64 med34 hard

Filter

Transmission log

// 120 visible

PYTHONDECODED.

Transmission log

What are common useful string methods?

What is the difference between '==' and 'is'?

What are mutable and immutable types in Python?

Why use virtual environments?

How does slicing with start:stop:step work?

How does iterable unpacking work?

How are Python dictionaries implemented and ordered?

How do you read TOML with tomllib in Python 3.11+?

What is uv and why is it replacing pip/poetry in 2025-26?

How do pyproject.toml, tomllib, and uv/pyproject workflows fit together?

What is the difference between a list and a tuple?

What set operations does Python support?

What are f-strings?

What is the difference between __repr__ and __str__?

How does the in operator work in Python?

How do you sort with a custom key, and how does sorted differ from sort?

How does comparison chaining (a < b < c) work?

What do enumerate and zip do?

What values are falsy in Python?

What is duck typing in Python?

What is the walrus operator?

How does exception handling work in Python?

What is the difference between shallow and deep copy?

What are mixins in Python?

How do uv workspaces and named dependency groups work?

What is the difference between an iterable and an iterator?

What are dunder (magic) methods?

What do the global and nonlocal keywords do?

What is structural pattern matching (match/case)?

How does Pydantic v2 validation work (BaseModel, field_validator, mode)?

What is the difference between bytes and str?

How does Polars LazyFrame query optimization work?

How does collections.deque work internally?

What is the @property decorator?

What is composition versus inheritance?

What are decorators in Python?

How do generator pipelines stream data lazily?

Polars vs pandas: when should you switch in 2025-26?

What useful types does the collections module provide?

What is the difference between a module and a package?

What are abstract base classes and Protocols?

What is the LEGB rule for scope resolution?

How does heapq work in Python?

How does a + b dispatch in Python?

What are lambda functions and map/filter/reduce?

What is the difference between classmethod and staticmethod?

How does exception propagation work up the call stack?

What do *args and **kwargs mean?

When do you use threading, multiprocessing, or asyncio?

What are dataclasses?

What is asyncio.TaskGroup and why does it replace gather?

How does a for loop work under the hood?

What are bound and unbound methods in Python?

How does yield from delegation work?

What is the difference between the call stack and the heap in Python?

How does functools.lru_cache work?

How do you raise and split ExceptionGroups manually?

How does functools.reduce fold a sequence?

Why use functools.wraps when writing decorators?

What are generators and why use them?

How does Python's name and object reference model work?

How does the bisect module work?

Why does Python cache small integers?

What is string interning in Python?

What does the functools module offer?

How does Timsort make Python's sort fast and stable?

What is the memory difference between a list comprehension and a generator expression?

What is the difference between class variables and instance variables?

What are generics and TypeVar in Python?

How do you enforce match/case exhaustiveness in Python?

What is Python 3.12's new type parameter syntax (type, generic classes)?

When should you still use multiprocessing vs free-threaded threads in Python 3.12+?

What are list/dict/set comprehensions?

What is a context manager?

What is monkey patching in Python?

What is a generator's lifecycle?

How does a Python list grow in memory?

How do you use multiple context managers at once?

What is the difference between repr and str?

What does slots do?

What is the difference between new and init?

What is the hash and eq contract?

What is the difference between getattr and getattribute?

What is the difference between del, del, and garbage collection?