[Python] Using Quantlib to calculate the Zspread of a treasury bond is returning a type...

This is the relevant part of my code:

def calculate_z_spread_ql(market_price, coupon_rate, maturity_date, yield_curve_handle, issue_date, leg):
"""
Calculate Z-spread using QuantLib with specified calendar and day count.
"""
calendar = ql.UnitedStates(ql.UnitedStates.GovernmentBond)
settlement_days = 2
face_value = 100
day_count = ql.ActualActual(ql.ActualActual.Bond)


#maturity_ql_date = ql.Date(maturity_date.day, maturity_date.month, maturity_date.year)
tenor = ql.Period(ql.Semiannual)

coupons = [coupon_rate]


schedule = ql.Schedule(issue_date, maturity_date, tenor, calendar,
ql.Unadjusted, ql.Unadjusted, ql.DateGeneration.Backward, False)
bond = ql.FixedRateBond(settlement_days, face_value, schedule, coupons, day_count)
bond.setPricingEngine(ql.DiscountingBondEngine(yield_curve_handle))

settlement_date = ql.Settings.instance().evaluationDate

includeSettlementDateFlows = True

#Error here, not sure why, all parameters are set up properly

z_spread = ql.CashFlows.zSpread(
leg, # Cash flows of the bond
market_price, # Market price of the bond
yield_curve_handle, # Yield curve handle
day_count, # Day count convention
ql.Compounded, # Compounding method (optional, default: Simple)
ql.Semiannual, # Frequency of compounding (optional, default: Annual)
includeSettlementDateFlows, # Include settlement date flows (optional, default: False)
settlement_date
) * 10000 # Convert to basis points

return z_spread

################################################ Main script ######################################################################

isin = 'US912810TX63' # Example 30yr ISIN

#global evaluation date is set to today
today = ql.Date().todaysDate()
ql.Settings.instance().evaluationDate = today

market_price, coupon_rate, maturity_date, issue_date, leg = fetch_bond_details_and_leg(isin)

maturities, yields = fetch_current_SOFR_yields()


yield_curve_handle = setup_quantlib_yield_curve(maturities, yields)

#This is for debugging only, curve set properly
print('################### cf in leg #######################')
for cf in leg: # Directly iterate over the leg to print details of each cash flow
print(f"Cash flow date: {cf.date()}, amount: {cf.amount()}")

print('################### maturities #######################')
print(maturities)
print('################### yields #######################')
print(yields)
print('################# yield_curve_handle #########################')
print_curve_details(yield_curve_handle)

print('################# z-spread calculations #########################')

z_spread = calculate_z_spread_ql(market_price, coupon_rate, maturity_date, yield_curve_handle, issue_date, leg)


What am I misssing?

I printed all the relevant inputs to the quantlib zpsread function as shown above and still something's not working in either the type or number of arguments, yet I think I set everything up correctly. ChatGPT not figuring it out either.

Here's the output with errors:

################### cf in leg #######################
Cash flow date: August 15th, 2024, amount: 2.124999999999999
Cash flow date: February 18th, 2025, amount: 2.124999999999999
Cash flow date: August 15th, 2025, amount: 2.124999999999999
Cash flow date: February 17th, 2026, amount: 2.124999999999999
Cash flow date: August 17th, 2026, amount: 2.124999999999999
Cash flow date: February 16th, 2027, amount: 2.124999999999999
Cash flow date: August 16th, 2027, amount: 2.124999999999999
Cash flow date: February 15th, 2028, amount: 2.124999999999999
Cash flow date: August 15th, 2028, amount: 2.124999999999999
Cash flow date: February 15th, 2029, amount: 2.124999999999999
Cash flow date: August 15th, 2029, amount: 2.124999999999999
Cash flow date: February 15th, 2030, amount: 2.124999999999999
Cash flow date: August 15th, 2030, amount: 2.124999999999999
Cash flow date: February 18th, 2031, amount: 2.124999999999999
Cash flow date: August 15th, 2031, amount: 2.124999999999999
Cash flow date: February 17th, 2032, amount: 2.124999999999999
Cash flow date: August 16th, 2032, amount: 2.124999999999999
Cash flow date: February 15th, 2033, amount: 2.124999999999999
Cash flow date: August 15th, 2033, amount: 2.124999999999999
Cash flow date: February 15th, 2034, amount: 2.124999999999999
Cash flow date: August 15th, 2034, amount: 2.124999999999999
Cash flow date: February 15th, 2035, amount: 2.124999999999999
Cash flow date: August 15th, 2035, amount: 2.124999999999999
Cash flow date: February 15th, 2036, amount: 2.124999999999999
Cash flow date: August 15th, 2036, amount: 2.124999999999999
Cash flow date: February 17th, 2037, amount: 2.124999999999999
Cash flow date: August 17th, 2037, amount: 2.124999999999999
Cash flow date: February 16th, 2038, amount: 2.124999999999999
Cash flow date: August 16th, 2038, amount: 2.124999999999999
Cash flow date: February 15th, 2039, amount: 2.124999999999999
Cash flow date: August 15th, 2039, amount: 2.124999999999999
Cash flow date: February 15th, 2040, amount: 2.124999999999999
Cash flow date: August 15th, 2040, amount: 2.124999999999999
Cash flow date: February 15th, 2041, amount: 2.124999999999999
Cash flow date: August 15th, 2041, amount: 2.124999999999999
Cash flow date: February 18th, 2042, amount: 2.124999999999999
Cash flow date: August 15th, 2042, amount: 2.124999999999999
Cash flow date: February 17th, 2043, amount: 2.124999999999999
Cash flow date: August 17th, 2043, amount: 2.124999999999999
Cash flow date: February 16th, 2044, amount: 2.124999999999999
Cash flow date: August 15th, 2044, amount: 2.124999999999999
Cash flow date: February 15th, 2045, amount: 2.124999999999999
Cash flow date: August 15th, 2045, amount: 2.124999999999999
Cash flow date: February 15th, 2046, amount: 2.124999999999999
Cash flow date: August 15th, 2046, amount: 2.124999999999999
Cash flow date: February 15th, 2047, amount: 2.124999999999999
Cash flow date: August 15th, 2047, amount: 2.124999999999999
Cash flow date: February 18th, 2048, amount: 2.124999999999999
Cash flow date: August 17th, 2048, amount: 2.124999999999999
Cash flow date: February 16th, 2049, amount: 2.124999999999999
Cash flow date: August 16th, 2049, amount: 2.124999999999999
Cash flow date: February 15th, 2050, amount: 2.124999999999999
Cash flow date: August 15th, 2050, amount: 2.124999999999999
Cash flow date: February 15th, 2051, amount: 2.124999999999999
Cash flow date: August 15th, 2051, amount: 2.124999999999999
Cash flow date: February 15th, 2052, amount: 2.124999999999999
Cash flow date: August 15th, 2052, amount: 2.124999999999999
Cash flow date: February 18th, 2053, amount: 2.124999999999999
Cash flow date: August 15th, 2053, amount: 2.124999999999999
Cash flow date: February 17th, 2054, amount: 2.124999999999999
Cash flow date: February 17th, 2054, amount: 100.0
################### maturities #######################
[1, 2, 3, 5, 7, 10, 20, 30]
################### yields #######################
[0.050895, 0.046245, 0.043525, 0.040827, 0.039832, 0.03928, 0.038740000000000004, 0.036802]
################# yield_curve_handle #########################
Reference Date: March 17th, 2025
Year 1: Zero Rate = 0.0462, Discount Factor = 0.9548
Year 2: Zero Rate = 0.0435, Discount Factor = 0.9166
Year 3: Zero Rate = 0.0422, Discount Factor = 0.8811
Year 4: Zero Rate = 0.0408, Discount Factor = 0.8493
Year 5: Zero Rate = 0.0403, Discount Factor = 0.8174
Year 6: Zero Rate = 0.0398, Discount Factor = 0.7874
Year 7: Zero Rate = 0.0396, Discount Factor = 0.7576
Year 8: Zero Rate = 0.0395, Discount Factor = 0.7293
Year 9: Zero Rate = 0.0393, Discount Factor = 0.7022
Year 10: Zero Rate = 0.0392, Discount Factor = 0.6755
Year 11: Zero Rate = 0.0392, Discount Factor = 0.6499
Year 12: Zero Rate = 0.0391, Discount Factor = 0.6254
Year 13: Zero Rate = 0.0391, Discount Factor = 0.6018
Year 14: Zero Rate = 0.0390, Discount Factor = 0.5792
Year 15: Zero Rate = 0.0390, Discount Factor = 0.5575
Year 16: Zero Rate = 0.0389, Discount Factor = 0.5366
Year 17: Zero Rate = 0.0388, Discount Factor = 0.5166
Year 18: Zero Rate = 0.0388, Discount Factor = 0.4974
Year 19: Zero Rate = 0.0387, Discount Factor = 0.4790
Year 20: Zero Rate = 0.0385, Discount Factor = 0.4626
Year 21: Zero Rate = 0.0384, Discount Factor = 0.4469
Year 22: Zero Rate = 0.0382, Discount Factor = 0.4319
Year 23: Zero Rate = 0.0380, Discount Factor = 0.4176
Year 24: Zero Rate = 0.0378, Discount Factor = 0.4039
Year 25: Zero Rate = 0.0376, Discount Factor = 0.3909
Year 26: Zero Rate = 0.0374, Discount Factor = 0.3783
Year 27: Zero Rate = 0.0372, Discount Factor = 0.3664
Year 28: Zero Rate = 0.0370, Discount Factor = 0.3549
Year 29: Zero Rate = 0.0368, Discount Factor = 0.3440
################# z-spread calculations #########################
Traceback (most recent call last):
File "H:\Python_KS\ZSpreadTest_QuantLib_Test.py", line 188, in <module>
z_spread = calculate_z_spread_ql(market_price, coupon_rate, maturity_date, yield_curve_handle, issue_date, leg)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "H:\Python_KS\ZSpreadTest_QuantLib_Test.py", line 143, in calculate_z_spread_ql
z_spread = ql.CashFlows.zSpread(
^^^^^^^^^^^^^^^^^^^^^
File "C:\ProgramData\anaconda3\envs\Khalil_Python\Lib\site-packages\QuantLib\QuantLib.py", line 15020, in zSpread
return _QuantLib.CashFlows_zSpread(*args)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: Wrong number or type of arguments for overloaded function 'CashFlows_zSpread'.
Possible C/C++ prototypes are:
CashFlows::zSpread(Leg const &,Real,ext::shared_ptr< YieldTermStructure > const &,DayCounter const &,Compounding,Frequency,bool,Date,Date,Real,Size,Rate)
CashFlows::zSpread(Leg const &,Real,ext::shared_ptr< YieldTermStructure > const &,DayCounter const &,Compounding,Frequency,bool,Date,Date,Real,Size)
CashFlows::zSpread(Leg const &,Real,ext::shared_ptr< YieldTermStructure > const &,DayCounter const &,Compounding,Frequency,bool,Date,Date,Real)
CashFlows::zSpread(Leg const &,Real,ext::shared_ptr< YieldTermStructure > const &,DayCounter const &,Compounding,Frequency,bool,Date,Date)
CashFlows::zSpread(Leg const &,Real,ext::shared_ptr< YieldTermStructure > const &,DayCounter const &,Compounding,Frequency,bool,Date)
CashFlows::zSpread(Leg const &,Real,ext::shared_ptr< YieldTermStructure > const &,DayCounter const &,Compounding,Frequency,bool)

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