如何使用嵌套循环，循环遍历数组元素？

Question

来自R background，我想在python中尝试嵌套for循环。我在下面的代码中循环遍历types的每次迭代时遇到问题。我的代码适用于types[0]，但不适用于连续迭代。我该如何解决这个问题？

import sys
import os
myfasta = sys.argv[1]
fasta = open(myfasta)
types = ['CDS', 'tRNA', 'rRNA']

for type in range(len(types)):
    print('My type index is: ' + str(type))
    flag = False
    for line in fasta:
        if line.startswith('>') and types[type] in line:
            flag = True
        elif line.startswith('>'):
          flag = False
        if flag:
            print(line.strip())

myfasta

>1_CDS
AAAAATTTCTGGGCCCCAAAAATTTCTGGGCCCC
AAAAATTTCTGGGCCCCAAAAATTTCTGGGCCCC
AAAAATTTCTGGGCCCCAAAAATTTCTGGGCCCC
GGGGTTTTTTT
>2_CDS
TTAAAAATTTCTGGGCCCCGGGAAAAAA
>3_CDS
TTTGGGAATTAAACCCT
>4_CDS
TTTGGGAATTAAACCCT
>5_rRNA
TTAAAAATTTCTGGGCCCCGGGAAAAAA
>6_tRNA
TTAAAAATTTCTGGGCCCCGGGAAAAAA

预期结果：

My type index is: 0
>1_CDS
AAAAATTTCTGGGCCCCAAAAATTTCTGGGCCCC
AAAAATTTCTGGGCCCCAAAAATTTCTGGGCCCC
AAAAATTTCTGGGCCCCAAAAATTTCTGGGCCCC
GGGGTTTTTTT
>2_CDS
TTAAAAATTTCTGGGCCCCGGGAAAAAA
>3_CDS
TTTGGGAATTAAACCCT
>4_CDS
TTTGGGAATTAAACCCT
My type index is: 1
>5_rRNA
TTAAAAATTTCTGGGCCCCGGGAAAAAA
My type index is: 2
>6_tRNA
TTAAAAATTTCTGGGCCCCGGGAAAAAA

Answer 1

您无法加载文件一次，并根据需要迭代它。

open()返回一个只能被消耗一次的迭代器。

调整代码以多次迭代文件

import sys
import os
myfasta = sys.argv[1]
types = ['CDS', 'tRNA', 'rRNA']

for type in range(len(types)):
    print('My type index is: ' + str(type))
    flag = False
    fasta = open(myfasta)
    for line in fasta:
        if line.startswith('>') and types[type] in line:
            flag = True
        elif line.startswith('>'):
          flag = False
        if flag:
            print(line.strip())

Answer 2

试试这段代码：

import sys
import os

myfasta = sys.argv[1]
with open(myfasta) as f:
    lines = f.readlines()
types = ['CDS', 'tRNA', 'rRNA']

for type_index, type in enumerate(types):
    print('My type index is:', type_index)
    flag = False
    for line in lines:
        if line.startswith('>') and type in line:
            flag = True
        elif line.startswith('>'):
            flag = False
        if flag:
            print(line.strip())

产量

My type index is: 0
>1_CDS
AAAAATTTCTGGGCCCCAAAAATTTCTGGGCCCC
AAAAATTTCTGGGCCCCAAAAATTTCTGGGCCCC
AAAAATTTCTGGGCCCCAAAAATTTCTGGGCCCC
GGGGTTTTTTT
>2_CDS
TTAAAAATTTCTGGGCCCCGGGAAAAAA
>3_CDS
TTTGGGAATTAAACCCT
>4_CDS
TTTGGGAATTAAACCCT
My type index is: 1
>6_tRNA
TTAAAAATTTCTGGGCCCCGGGAAAAAA
My type index is: 2
>5_rRNA
TTAAAAATTTCTGGGCCCCGGGAAAAAA