If you are referring to the number of bits in a circular/Morgan fingerprint, you can set this directly in RDKit using the 'nBits' parameter. For example:
>>from rdkit import Chem
>>from rdkit.Chem import AllChem
>>mol = Chem.MolFromSmiles('c1ccccc1')
>>fp = AllChem.GetMorganFingerprintAsBitVect(mol, radius=2, nBits=512)
If you wish to access the fingerprint data, you can e.g. access methods which tell you which bits are 'on', or the entire bitstring itself:
>>bits = fp.ToBitString()
>>[out] "0000000000000000................00000000000000000"
>>len(bits)
>>[out] 512
其他分子指纹
http://www.rdkit.org/docs/GettingStartedInPython.html#fingerprinting-and-molecular-similarity
文章来源: 二进制摩根分子指纹的输出