Python Tricks I Actually Reach For Daily

<Alert type="note" title="When NOT to use walrus">
  Don't force it into existing clean code. If the assignment belongs outside the condition, put it there. The walrus shines in: loop guards, catch blocks, and reducing duplicated function calls.
</Alert>

<Quiz
  question="When is the walrus operator `:=` most valuable?"
  options={[
    "In simple variable assignments like `x := 5`",
    "In loop guards and reducing duplicated function calls",
    "To replace all `=` assignments",
    "When you want to make code shorter no matter what"
  ]}
  correctIndex={1}
  explanation="The walrus shines in loop guards (`while (line := f.readline())`), catch blocks (`except Exception as e`), and avoiding duplicate calls (`if (n := expensive()) > 10`). Don't force it where simple assignment is clearer."
/>

</AccordionItem>

<AccordionItem title="8. f-strings from Python 3.12+">

Python 3.12 added f-string debugging with <code>=</code> and multiline f-strings:

```python filename="fstrings.py"
name, age = "Alice", 30

# Debug mode — shows expression + value
print(f"{name=} {age=}")  # name='Alice' age=30

# Multiline (no more backslash continuation)
report = f"""
Name:   {name}
Status: {"Adult" if age >= 18 else "Minor"}
Score:  {95.5:.1f}%
"""

from pathlib import Path

base = Path("/app/data")

# Fluent chaining — works cross-platform
config = base / "config" / f"env_{ENV}.yaml"
logs   = base / "logs" / "app.log"

# Read/write without manual open()
text = config.read_text(encoding="utf-8")
config.write_text(new_text, encoding="utf-8")

# Existence checks
if config.exists() and config.is_file():
size = config.stat().st_size

# Iterate directory
for log_file in base.glob("**/*.log"):
print(log_file.name, log_file.stat().st_size)

from dataclasses import dataclass, field
from typing import List

@dataclass
class Project:
name: str
slug: str
tags: List[str] = field(default_factory=list)
starred: bool = False

# ✅ Auto-generated __init__, __repr__, __eq__
p = Project(
name="Portfolio",
slug="portfolio",
tags=["nextjs", "tailwind"],
starred=True,
)
print(p)  # Project(name='Portfolio', slug='portfolio', ...)

# ✅ Frozen dataclass = immutable (no keyword mutability issues)
from dataclasses import dataclass

@dataclass(frozen=True)
class Point:
x: float
y: float

pt = Point(1.0, 2.0)
# pt.x = 3.0  # FrozenInstanceError

from collections import defaultdict
from contextlib import contextmanager
from threading import Lock

# Grouping — defaultdict eliminates "if key in dict" checks
grouped = defaultdict(list)
for item in items:
grouped[item.category].append(item)

# Custom context manager for timing
@contextmanager
def timer(label):
import time
start = time.perf_counter()
yield
elapsed = time.perf_counter() - start
print(f"{label}: {elapsed*1000:.2f}ms")

with timer("database query"):
results = db.query("SELECT * FROM users")