def find_amplicon_pos(df):
	"""
	Find amplicon position from a list of matches.
	Returns a tuple (start, stop).
	
	Will return the first occurence of a match on the + strand followed by a match on the minus strand.
	"""
	dfs = df.sort_values(by='start')
	start = None
	for index, row in dfs.iterrows():
		if row["strand"] == 'plus' and not start: 
			start = row['start']
		elif row['strand'] == 'minus' and start:
			end = row['start'] # blast reports end as the 3' position of the primer on the reverse strand
			return (start, end)