def find_primers(target_dna, user_parameters, search_range):
primers = []
if target_dna.len < 500:
ideal_len = (16, 18)
elif target_dna.len > 2500:
ideal_len = (20, 24)
else:
ideal_len = (17, 22)
search_start = max(0, target_dna.start-search_range)
for i in range(search_start, target_dna.start+1):
for j in range(ideal_len[0], ideal_len[1]+1):
primer = Primer(target_dna, i, i+j)
parameters = primer.parameters()
if user_parameters[0][0] <= parameters[0] <= user_parameters[0][1] and\
user_parameters[1][0] <= parameters[1] <= user_parameters[1][1] and\
not parameters[3] and not parameters[4] and parameters[5]:
if user_parameters[2] == None:
primers.append(primer)
else:
if user_parameters[2] == parameters[2]:
primers.append(primer)
return primers
