我正试图在python中创建一个函数,该函数从fasta文件中读取明确和不明确的核苷酸序列,并返回序列ID和分子量。
我用以下代码尝试了这个:
import Bio
from Bio import SeqUtils, SeqIO
def function(filename):
nucleotides ={'A','T', 'C', 'G'}
with open(filename) as file:
for record in SeqIO.parse(file, "fasta"):
for nucl in record:
if nucl in nucleotides:
continue
else:
print(str(record.id)+": is ambiguous")
break
else:
mol_weight= Bio.SeqUtils.molecular_weight(record)
print(str(record.id)+": is unambiguous & molecular weight = "+str(mol_weight))
function("random.fasta")
如果我在不明确的序列上使用这个代码,绝对没有问题,我会得到我想要的结果。然而,如果我包括明确的序列,我得到";ValueError:"I"不是一个有效的明确的DNA字母是由"Bio.SeqUtils.molecule_weight(record("函数引起的,在我看来,这是没有意义的,因为如果我正确的话,字母"I"通常会导致第一个else语句的中断。
我还使用了一个自定义函数来手动计算分子量(基于固定值(,在这种情况下没有错误,该函数对不明确和不明确的序列都很好。然而,有人指出,我的手动计算不如内置函数准确。
我对Python有点陌生,但我希望有人能知道为什么ValueError仍然会发生,以及如何解决它
我认为错误发生在表达式mol_weight= Bio.SeqUtils.molecular_weight(record)
中。
记录被隐式地转换为它的字符串表示ID: SEQUENCE_1 ...
。因此,ValueError中的'I'
根本不对应于核苷酸,而是相当随机的字符串值。
请尝试以下行:mol_weight = Bio.SeqUtils.molecular_weight(record.seq)
对我来说,它返回了想要的结果:
SEQUENCE_1: is unambiguous & molecular weight = 331.2218
对于一个琐碎的序列(只有字母a(,它之前会引发您描述的错误。
>SEQUENCE_1
A
更新:
完整的解决方案如下:
from Bio import SeqIO, SeqUtils
def function(filename):
with open(filename) as file:
for record in SeqIO.parse(file, "fasta"):
try:
mol_weight = SeqUtils.molecular_weight(record.seq)
print(f"{record.id}: is unambiguous & molecular weight = {mol_weight}")
except ValueError as exception:
print(f"{record.id}: {exception}")
if __name__ == '__main__':
function("random.fasta")
我包含了@pippo1980答案中的exeception处理,因为它确实更简单、更快,而且可以说更像蟒蛇。
较短:
from Bio import SeqIO, SeqUtils
def function(filename):
with open(filename) as file:
for record in SeqIO.parse(file, "fasta"):
try:
mol_weight= SeqUtils.molecular_weight(record.seq, 'DNA')
print(str(record.id)+": is unambiguous & molecular weight = "+str(mol_weight))
except Exception as exception:
print(record.id+':',str(type(exception).__name__), str(exception))
function("random.fasta")
function("random.fasta")
输入random.fasta文件:
>first
AAAAAAAAAAAAATTTTTTTTTTTTTTGGGGGGGGGGGGGGCCCCCCCCCCCCCCGTA
>second
AAAAAAAAAAAAAAAAAAAAATTTTTTTTTTTTTTTTICCCCCCCCCCCCCCCCCCCCCCCCCCC
>third
AAAAAAAAAQQQQQQQQQQQQQQQQQQTTTTTTTTTT
>fourth
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAATTTTTTTTTTTTTTTTTGGGGGGGGGGGGGGGGGCGCGCGCGCGC
输出:
first: is unambiguous & molecular weight = 17952.438
second: ValueError 'I' is not a valid unambiguous letter for DNA
third: ValueError 'Q' is not a valid unambiguous letter for DNA
fourth: is unambiguous & molecular weight = 25755.56080000001