How can I print many significant figures in Python?

Question

For a scientific application I need to output very precise numbers, so I have to print 15 significant figures. There are already questions on this topic here, but they all c

Answer 1

Thought the original question wanted to format n significant figures, not n decimal points. So a custom function might be required until some more native built-in types are on offer? So you'll want something like:

def float_nsf(q,n):
    """
    Truncate a float to n significant figures.  May produce overflow in 
    very last decimal place when q < 1.  This can be removed by an extra 
    formatted print. 
    Arguments:
      q : a float
      n : desired number of significant figures
    Returns:
    Float with only n s.f. and trailing zeros, but with a possible small overflow.
    """
    sgn=np.sign(q)
    q=abs(q)
    n=int(np.log10(q/10.)) # Here you overwrite input n!
    if q<1. :
        val=q/(10**(n-1))
        return sgn*int(val)*10.**(n-1)
    else:
        val=q/(10**n)
        return sgn*int(val)*10.**n