effect_size : float
standardized effect size, mean divided by the standard deviation.
effect size has to be positive.
nobs : int or float
sample size, number of observations.
alpha : float in interval (0,1)
significance level, e.g. 0.05, is the probability of a type I
error, that is wrong rejections if the Null Hypothesis is true.
df : int or float
degrees of freedom. By default this is None, and the df from the
one sample or paired ttest is used, df = nobs1 - 1
alternative : string, ‘two-sided’ (default), ‘larger’, ‘smaller’
extra argument to choose whether the power is calculated for a
two-sided (default) or one sided test. The one-sided test can be
either ‘larger’, ‘smaller’.