如何使用嵌套循环，遍历数组元素？

Question

来自 R 背景，我想尝试 python 中的嵌套 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？

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

您不能一次加载文件就可以随心所欲地对其进行迭代。

open() returns一个迭代器，只能消费一次

调整您的代码以多次迭代您的文件

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

试试这个代码：

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())

输出

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

如何使用嵌套循环，遍历数组元素？

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python

fasta