如何仅显示前20项

Question

这里的Python代码为我提供了我想要的输出。不过，我需要帮助，将结果限制在前20行。

输入示例如下所示，

gi|170079688|ref|YP_001729008.1|双功能核黄素激酶/FMN腺苷酰转移酶大肠杆菌str.K-12 substr.RNEQRFASLDELKAQIARDELTAREFFGLTKPA gi|170079689|ref|YP_001729009.1| gi|170079689|ref|YP_001729009.1|isoleucyl tRNA合成酶大肠杆菌str.K-12 substr.gi|170079690|ref|YP_001729010.1|脂蛋白信号肽酶大肠杆菌str。K-12 substr.DH10B

import re

id = None
header = None
seq = ''

a_file = open('e_coli.faa')

for line in a_file:
    m = re.match(">(\S+)\s+(.+)", line.rstrip())
    if m:
        if id is not None:

            print("{0} length:{1} {2}".format(id, len(seq),header))

        id, header = m.groups()
        seq = ''
    else:
        seq += line.rstrip()

Answer 1

在最上面添加c = 0。然后，改变

        print("{0} length:{1} {2}".format(id, len(seq),header))

至

        if c < 10:
            print("{0} length:{1} {2}".format(id, len(seq),header))
            c += 1

有几处调整后的结果：

import re

id = None
header = None
seq = ''

with open('e_coli.faa') as a_file:
    for line in a_file:
        m = re.match(">(\S+)\s+(.+)", line.rstrip())
        if m:
            if id and c < 20:
                print("{0} length:{1} {2}".format(id, len(seq),header))
                c += 1

            id, header = m.groups()
            seq = ''
        else:
            seq += line.rstrip()

读取文件的前20行。您可以使用readlines()

而不是：

for line in a_file:

用途：

for line in a_file.readlines()[:20]: