Added a new function for proper polyA addition

sequence_extractor/polyA.py

 import numpy as np
 # To do: Taking probabilities of nucleotides from user and raising error if sum != 1
-def PolyA_generator(
+def polyA_generator(
 	exon: str,
 ) -> str:
 	"""Adds a PolyA tail to an exon sequence input into the function.
@@ -14,3 +14,23 @@ def PolyA_generator(
 	listA = ['A','T','G','C']
 	polyA = ''.join(np.random.choice(listA,250,p=[0.9,0.040,0.020,0.020]))
 	return (exon+polyA)
+
+def polyA_addition_to_fasta_list(
+	fasta_list: list,
+) -> list:
+	"""Takes in a list of alternate annotations and exons and outputs a list where polyA tail has been added to all the exon 3' ends.
+
+	Args:
+		fasta_list: List contaning annotations and exons, with every element being an equivalent to a line in the fasta file
+
+	Returns:
+		A list like the initial list, this time with polyA tail added onto it.
+	"""
+	list_annotation = fasta_list[0::2]
+	list_exon = fasta_list[1::2]
+	mature_rna_list = [polyA_generator(i) for i in list_exon]
+	final_list = []
+	for annotation, exon in zip(list_annotation,mature_rna_list):
+		final_list.append(annotation)
+		final_list.append(exon)
+	return final_list