this is incredibly expensive, performing O(n*m) comparisions where n is the number of nucleotides and m is the number of degen bases. Regex may be faster, but this is also going to be much faster:

```python
IUPAC_AMBIG_CHARS = set("RYMKWSBDHVN") # this should be centralized somewhere, why not pull from cogent?
def count_ambig(curr_seq, ambig_chars=IUPAC_AMBIG_CHARS):
    """Counts non-ambiguous characters in seq
    
    curr_seq: fasta sequence
    ambig_chars: nucleotide characters"""
	return sum([n in ambig_chars for n in curr_seq])
```