Standard Student’s t distribution with df degrees of freedom.
A special case of the hyperbolic distribution. As df gets large, the result resembles that of the standard normal distribution (standard_normal).
Parameters:  df : int
size : int or tuple of ints, optional


Returns:  samples : ndarray or scalar

Notes
The probability density function for the t distribution is
The t test is based on an assumption that the data come from a Normal distribution. The t test provides a way to test whether the sample mean (that is the mean calculated from the data) is a good estimate of the true mean.
The derivation of the tdistribution was forst published in 1908 by William Gisset while working for the Guinness Brewery in Dublin. Due to proprietary issues, he had to publish under a pseudonym, and so he used the name Student.
References
[R223]  Dalgaard, Peter, “Introductory Statistics With R”, Springer, 2002. 
[R224]  Wikipedia, “Student’s tdistribution” http://en.wikipedia.org/wiki/Student’s_tdistribution 
Examples