stats.py 文件源码

def ppf(x, n):
    try:
        from scipy import stats
    except ImportError:
        stats = None

    if stats:
        if n < 30:
            return stats.t.ppf(x, n)
        return stats.norm.ppf(x)
    else:
        if n < 30:
            # TODO: implement power series:
            # http://eprints.maths.ox.ac.uk/184/1/tdist.pdf
            raise ImportError(
                'You must have scipy installed to use t-student '
                'when sample_size is below 30')
        return norm_ppf(x)

# According to http://sphweb.bumc.bu.edu/otlt/MPH-Modules/BS/
# BS704_Confidence_Intervals/BS704_Confidence_Intervals_print.html