Removing headlines in fasta file in python

I want to remove the headlines of a fasta file that contains multiple protein sequences. I need to count the amino acid numbers.

>Os12t0641500-03 Similar to RecF/RecN/SMC N terminal domain containing protein, expressed.
MAAAAAGKGGGGQGRIHRLEVENFKSYKGTQTIGPFFDFTAIIGPNGAGKSNLMDAISFV
LIKVPLL*
>Os12t0597800-01 Similar to Helix-loop-helix DNA-binding domain containing protein, expressed.
MMSFPYSSGDLGEATTAAAAAVDMITLDQMFRDYDASTGDDLFELVWESCGGGEIDSGAG
LGRQ*
>Os12t0598600-00 Similar to H0315A08.1 protein.
MKRSMNYSGIECFTFGDDNKLRIFPPNSYKFKPKDHIILDEVQECILDNFWYQYNNKREE
FSDLDTMDLGGHGQPDE*