Regex, Date & Time

import re

log = "2026-09-20 14:03:11 ERROR user=ada id=4021 msg=\"payment failed\" ip=10.0.0.7"

# search: the first match, or None. Groups pull pieces out.
m = re.search(r"user=(\w+) id=(\d+)", log)
print(m.group(0), "|", m.group(1), m.group(2))

# named groups read better
m = re.search(r"(?P<date>\d{4}-\d{2}-\d{2}) (?P<time>[\d:]+) (?P<level>[A-Z]+)", log)
print(m.groupdict())

# findall: every match
print(re.findall(r"\d+\.\d+\.\d+\.\d+", log))
print(re.findall(r"(\w+)=", log))          # every key

# sub: replace, with a backreference
print(re.sub(r"id=\d+", "id=***", log)[:40])
print(re.sub(r"(\d{4})-(\d{2})-(\d{2})", r"\3/\2/\1", "due 2026-09-20"))

# compile once when used in a loop; flags
email = re.compile(r"^[\w.+-]+@[\w-]+\.[\w.]+$", re.IGNORECASE)
for s in ["[email protected]", "not an email", "[email protected]"]:
    print(f"{s!r:28} {bool(email.match(s))}")

# split on a pattern
print(re.split(r"[,;\s]+", "a, b;c   d"))

from datetime import date, datetime, timedelta

d = date(2026, 9, 20)
print(d, d.year, d.month, d.weekday(), d.strftime("%A"))    # Monday=0

dt = datetime(2026, 9, 20, 14, 30)
print(dt, "|", dt.date(), "|", dt.time(), "|", dt.hour)

# arithmetic
print(d + timedelta(days=45))
print(date(2026, 12, 25) - d)                # a timedelta
print((date(2026, 12, 25) - d).days, "days to go")
print(dt + timedelta(hours=36))

week = timedelta(weeks=1)
print(week.total_seconds(), week / timedelta(hours=1))

# comparing
print(d < date(2027, 1, 1), max(d, date(2025, 1, 1)))

# replacing parts
print(d.replace(day=1), dt.replace(minute=0, second=0))

# ISO format round-trip — the one string format you should default to
s = dt.isoformat()
print(s, datetime.fromisoformat(s) == dt)

from datetime import datetime

dt = datetime(2026, 9, 20, 14, 5, 9)
print(dt.strftime("%Y-%m-%d"))
print(dt.strftime("%d/%m/%Y %H:%M"))
print(dt.strftime("%A, %d %B %Y at %I:%M %p"))
print(dt.strftime("%b %-d") if hasattr(dt, "strftime") else "")   # platform-specific: no leading zero on Linux/macOS
print(f"{dt:%Y%m%d_%H%M%S}")                # f-strings accept the same directives

# parsing: the pattern must match the text exactly
print(datetime.strptime("20/09/2026 14:05", "%d/%m/%Y %H:%M"))
print(datetime.strptime("Sep 20 2026", "%b %d %Y").date())
print(datetime.strptime("2026-09-20T14:05:09Z", "%Y-%m-%dT%H:%M:%SZ"))

from datetime import datetime, timezone, timedelta

# timestamp → aware datetime (say UTC explicitly!)
ts = 1_790_000_000
utc = datetime.fromtimestamp(ts, tz=timezone.utc)
print(utc, utc.tzinfo)
print(int(utc.timestamp()) == ts)

# fixed-offset zones: fine for display when you know the offset
IST = timezone(timedelta(hours=5, minutes=30), "IST")
EDT = timezone(timedelta(hours=-4), "EDT")
kolkata = utc.astimezone(IST)
nyc = utc.astimezone(EDT)
print(kolkata.strftime("%Y-%m-%d %H:%M %Z"), "|", nyc.strftime("%Y-%m-%d %H:%M %Z"))
print(kolkata == nyc == utc)            # same instant, three clocks

# build an aware datetime from local wall-clock time
BST = timezone(timedelta(hours=1), "BST")
meeting = datetime(2026, 9, 21, 9, 0, tzinfo=BST)
print(meeting.astimezone(timezone.utc))
print(meeting.isoformat())

# naive vs aware
naive = datetime(2026, 9, 21, 9, 0)
print(naive.tzinfo, "→ naive")
try:
    print(meeting - naive)
except TypeError as e:
    print("TypeError:", e)
aware = naive.replace(tzinfo=timezone.utc)      # attach a zone (does NOT convert)
print(meeting - aware)                          # -1 hour, printed as Python prints negative timedeltas

import time

start = time.perf_counter()
total = sum(range(2_000_000))
elapsed = time.perf_counter() - start
print(total, "computed in under a second:", elapsed < 1.0)

# exponential backoff with a cap
def backoff_schedule(attempts, base=1.0, cap=30.0):
    return [min(cap, base * 2 ** i) for i in range(attempts)]
print(backoff_schedule(6))

time.sleep(0.05)            # 50 ms — real programs sleep between retries, not in loops
print("slept")

print(type(time.time()).__name__, time.time() > 1_700_000_000)