How to format huge reals?

edit

Thank you Volker! So let's give it a try:

def SciFormat(f, n) :
    s = f.str()
    t = ""
    count = 0
    w = true
    for c in s :
        if c <> 'e' and w :
            if count < n+2 :
                t += c
                count += 1
        else :
            t += c
            w = false
    return t        

b = 2.2379923576571269975e4767529
print b.parent()
for i in (0..20): print SciFormat(b, i)  

Real Field with 67 bits of precision
2.e4767529
2.2e4767529
2.23e4767529
2.237e4767529
2.2379e4767529
2.23799e4767529
2.237992e4767529
2.2379923e4767529
2.23799235e4767529
2.237992357e4767529
2.2379923576e4767529
2.23799235765e4767529
2.237992357657e4767529
2.2379923576571e4767529
2.23799235765712e4767529
2.237992357657126e4767529
2.2379923576571269e4767529
2.23799235765712699e4767529
2.237992357657126998e4767529
2.237992357657126998e4767529
2.237992357657126998e4767529

Please suggest improvements.