Calendars and the Good Friday exception

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Worked examples

Read the claim, then run it and check the machine agrees. One at a time — nothing here is taken on trust.

Example 1 of 2 One date, three markets, two answers

example.py

import QuantLib as ql

usgov = ql.UnitedStates(ql.UnitedStates.GovernmentBond)   # SIFMA - drives SOFR
target = ql.TARGET()                                       # eurosystem - drives ESTR
uk = ql.UnitedKingdom()                                    # drives SONIA

gf26, gf27 = ql.Date(3, 4, 2026), ql.Date(26, 3, 2027)    # Good Fridays
for name, cal in (("USGOV", usgov), ("TARGET", target), ("UK", uk)):
    print(f"{name:6}  open Good Friday 2026: {str(cal.isBusinessDay(gf26)):5}"
          f"   open Good Friday 2027: {cal.isBusinessDay(gf27)}")

2026: the US bond market trades while all of Europe is dark — April 3 is the first Friday of the month, so the jobs report drops and SIFMA stays open. 2027: Good Friday falls in March, no report, and all three calendars agree it's a holiday. Same rule name, "Good Friday", two different realities — isBusinessDay is the only opinion that counts.

Example 2 of 2 Dump the list, don't trust the rule

example.py

import QuantLib as ql

target = ql.TARGET()
hols = target.holidayList(ql.Date(1, 1, 2026), ql.Date(31, 12, 2026))
print("TARGET weekday holidays 2026:", [d.ISO() for d in hols])

uk = ql.UnitedKingdom()
mon = ql.Date(28, 12, 2026)   # the Monday after Boxing Day (Sat 26 Dec)
print("UK     open Mon 28 Dec 2026:", uk.isBusinessDay(mon))
print("TARGET open Mon 28 Dec 2026:", target.isBusinessDay(mon))

Five weekday holidays in TARGET's whole 2026 — and Boxing Day isn't one of them, because 26 December is a Saturday and a TARGET holiday landing on a weekend simply disappears (no substitute day). The UK disagrees: it substitutes the lost holiday to Monday the 28th, so London is closed on a day Frankfurt settles euros. holidayList is also your golden-test tool: dump it, diff it against the exchange's published list, and your calendar is proven for that year rather than assumed.

Check the concept

One question at a time. Unsure? Revisit the lecture, then answer.

Question 1 of 4

Why is 3 April 2026 — Good Friday — a business day on the US government-bond calendar?

the US bond market never observes Good Friday it's the first Friday of April: the employment report is released, and SIFMA keeps the market open QuantLib's US calendar is missing Good Friday because TARGET is closed, US markets must stay open to provide liquidity

The challenge

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