As it is part of fasta file, so you are going to slice it like this:
>>> import re
>>> a = "TCGATCATCGATCG>IonTorrenttrimmedcontig1$CCGTAGGTGAACCTGCGGAAG"
>>> re.split(">[^$]*\$", a)
['TCGATCATCGATCG', 'CCGTAGGTGAACCTGCGGAAG']
Also, some people are answering with slicing with '>ion1'. That's totally wrong!
I believe your problem is solved! I am also editing a tag with bioinformatics for this question!