[Python] In "statsmodels" Python library, why does z-test not require Population standard...

So to execute a z-test in python, I have seen people doing:

from statsmodels.stats.weightstats import ztest as ztest
# IQ levels of 20 patients post medication
data = [88, 92, 94, 94, 96, 97, 97, 97, 99, 99,
105, 109, 109, 109, 110, 112, 112, 113, 114, 115]

ztest(data, value=100) # value is mean


Why is the Population standard deviation (std) not required in the argument? How does the library apply the z-test formula without getting the population std?

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