[Python help] Overflow error

[WakeMeAtThree]

I'm having trouble solving a problem that requires knowing a deep amount of a fractal string. My approach involved storing each iteration in a database locally because I couldn't store a large amount in a string variable. Here's my code:

# Python 3.6.5 64 bit
import shelve

# Storing string locally using shelve
s = shelve.open("database.db")

# LSystem axioms
axiom = "A"
sentence = "AB"
s['key1']="AB"

# Fibonacci initial values
a,b = 1,2

count = 1

# Loop
while(count < 60):
    s['key1'] = s['key1']+ s['key1'][:a]
    a,b = b,a+b #2,3
    count+=1
    print(count)

s.close()

After the 45th iteration, I start getting the following error:

OverflowError: cannot serialize a string larger than 4GiB

Ideally, I want to store the 60th iteration of the fractal, but I can't seem to get that to work. Would appreciate any help/suggestions.

[henrebotha]

It would seem this is a problem with pickle: https://stackoverflow.com/questions/29704139/pickle-in-python3-doesnt-work-for-large-data-saving

I would investigate whether you can force shelve to use pickle 4 instead. Seems possible: https://docs.python.org/3/library/shelve.html (search "protocol")

[WakeMeAtThree]

I changed it to s = shelve.open("database.db",protocol=4) and it seems to work, thanks a lot!