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Time zones, money & measurement units

Make temporal and numeric meaning explicit before aggregation.

Apply this to your Python data tools, PixelFed quality work, n8n integrations or BI delivery when the project needs it.

Understand the idea

A timestamp without a time zone is ambiguous until a source contract supplies its meaning. The event time and the time your process fetched the event answer different questions. Keep both when freshness affects a downstream decision.

A currency amount and an exchange rate need different precision policies. EGP minor units work well for many expense amounts, but a forex rate may require more than two decimal places. Do not truncate a rate using the ledger’s amount parser. On Windows, install the first-party tzdata package in the project environment if IANA zone data is unavailable.

What to learn

• Store event and ingestion timestamps separately as aware UTC instants.
• Convert to Africa/Cairo for display or a documented business date.
• Use validated Decimal values or integer minor units with a rounding policy.

A small original example

from datetime import datetime, timezone
from zoneinfo import ZoneInfo

instant = datetime(2026, 11, 1, 12, tzinfo=timezone.utc)
local = instant.astimezone(ZoneInfo("Africa/Cairo"))
print(instant.isoformat(), local.isoformat())

Practice on your own data

Design a quote fixture contract with provider_as_of, fetched_at, rate precision, base and quote currency. Test an invalid date and stale quote.

Practice this lesson in the Python lab →

Prerequisites

Variables, types & missing values · Files, CSV, JSON & paths · APIs, JSON & failure policies

Sources and further reading

• Python · IANA time zones ↗Official project documentation
• Python language tutorial ↗Official documentation

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