我们有一个很大的原始数据文件,我们想把它修剪成指定的大小。

如何在python中获取文本文件的前N行?所使用的操作系统对实现有任何影响吗?


当前回答

这对我很有效

f = open("history_export.csv", "r")
line= 5
for x in range(line):
    a = f.readline()
    print(a)

其他回答

这适用于Python 2和3:

from itertools import islice

with open('/tmp/filename.txt') as inf:
    for line in islice(inf, N, N+M):
        print(line)

Python 3:

with open("datafile") as myfile:
    head = [next(myfile) for x in range(N)]
print(head)

Python 2:

with open("datafile") as myfile:
    head = [next(myfile) for x in xrange(N)]
print head

下面是另一种方法(Python 2和3都是):

from itertools import islice

with open("datafile") as myfile:
    head = list(islice(myfile, N))
print(head)
N = 10
with open("file.txt", "a") as file:  # the a opens it in append mode
    for i in range(N):
        line = next(file).strip()
        print(line)

我自己最方便的方法:

LINE_COUNT = 3
print [s for (i, s) in enumerate(open('test.txt')) if i < LINE_COUNT]

基于列表理解的解决方案 函数open()支持迭代接口。enumerate()包含open()和return元组(index, item),然后检查是否在可接受的范围内(如果i < LINE_COUNT),然后简单地打印结果。

欣赏Python。;)

我所做的就是用熊猫形来称呼N行。我认为性能不是最好的,但是举个例子,如果N=1000:

import pandas as pd
yourfile = pd.read_csv('path/to/your/file.csv',nrows=1000)