如何仅显示前20个条目

Question

这里的Python代码为我提供了我想要的输出。但是，我需要帮助将结果限制为前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腺苷酸转移酶[大肠杆菌str。 K-12 substr。 DH10B] MKLIRGIHNLSQAPQEGCVLTIGNFDGVHRGHRALLQGLQEEGRKRNLPVMVMLFEPQPLELFATDKAPA RLTRLREKLRYLAECGVDYVLCVRFDRRFAALTAQNFISDLLVKHLRVKFLAVGDDFRFGAGREGDFLLL QKAGMEYGFDITSTQTFCEGGVRISSTAVRQALADDNLALAESLLGHPFAISGRVVHGDELGRTIGFPTA NVPLRRQVSPVKGVYAVEVLGLGEKPLPGVANIGTRPTVAGIRQQLEVHLLDVAMDLYGRHIQVVLRKKI RNEQRFASLDELKAQIARDELTAREFFGLTKPA gi | 170079689 | ref | YP_001729009.1 |异亮氨酰-tRNA合成酶[大肠杆菌str。 K-12 substr。 DH10B] MSDYKSTLNLPETGFPMRGDLAKREPGMLARWTDDDLYGIIRAAKKGKKTFILHDGPPYANGSIHIGHSV NKILKDIIVKSKGLSGYDSPYVPGWDCHGLPIELKVEQEYGKPGEKFTAAEFRAKCREYAATQVDGQRKD FIRLGVLGDWSHPYLTMDFKTEANIIRALGKIIGNGHLHKGAKPVHWCVDCRSALAEAEVEYYDKTSPSI DVAFQAVDQDALKAKFAVSNVNGPISLVIWTTTPWTLPANRAISIAPDFDYALVQIDGQAVILAKDLVES VMQRIGVTDYTILGTVKGAELELLRFTHPFMGFDVPAILGDHVTLDAGTGAVHTAPGHGPDDYVIGQKYG LETANPVGPDGTYLPGTYPTLDGVNVFKANDIVVALLQEKGALLHVEKMQHSYPCCWRHKTPIIFRATPQ WFVSMDQKGLRAQSLKEIKGVQWIPDWGQARIESMVANRPDWCISRQRTWGVPMSLFVHKDTEELHPRTL ELMEEVAKRVEVDGIQAWWDLDAKEILGDEADQYVKVPDTLDVWFDSGSTHSSVVDVRPEFAGHAADMYL EGSDQHRGWFMSSLMISTAMKGKAPYRQVLTHGFTVDGQGRKMSKSIGNTVSPQDVMNKLGADILRLWVA STDYTGEMAVSDEILKRAADSYRRIRNTARFLLANLNGFDPAKDMVKPEEMVVLDRWAVGCAKAAQEDIL KAYEAYDFHEVVQRLMRFCSVEMGSFYLDIIKDRQYTAKADSVARRSCQTALYHIAEALVRWMAPILSFT ADEVWGYLPGEREKYVFTGEWYEGLFGLADSEAMNDAFWDELLKVRGEVNKVIEQARADKKVGGSLEAAV TLYAEPELSAKLTALGDELRFVLLTSGATVADYNDAPADAQQSEVLKGLKVALSKAEGEKCPRCWHYTQD VGKVAEHAEICGRCVSNVAGDGEKRKFA gi | 170079690 | ref | YP_001729010.1 |脂蛋白信号肽酶[大肠杆菌str。 K-12 substr。 DH10B] MSQSICSTGLRWLWLVVVVIDIDLGSKYLILQNFALGDTVPLFPSLNLHYARNYGAAFSFLADSGGWQRW FFAGIAIGISVILAVMMYRSKATQKLNNIAYALIIGGALGNLFDRLWHGFVVDMIDFYVGDWHFATFNLA DTAICVGAALIVLEGFLPSRAKKQ

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

在最顶部，添加c = 0。然后，更改

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

to

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

---

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]:

Answer 2

使用切片运算符：

with open('e_coli.faa', 'r') as f:
    content = f.readlines()

for line in content[:20]:
    print(line)

Answer 3

使用enumerate()

for idx, line in enumerate(a_file):
    if idx < 20:
        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()
    else:
        break