如何使用Python csv阅读器遍历特定范围的行？

Question

如何使用Python csv阅读器遍历特定范围的行？

下面的代码遍历所有行：

with open(trainFile, 'rt') as csvfile: 
    spamreader = csv.reader(csvfile, delimiter=' ', quotechar='|') 
    for row in spamreader: 
     print (', '.join(row)) 

我只能从给定的希望环路（i到j）。

Answer 1

您可以使用itertools.islice：

import itertools 

i, j = 10, 20 
with open(trainFile, 'rt') as csvfile: 
    spamreader = csv.reader(csvfile, delimiter=' ', quotechar='|') 
    for row in itertools.islice(spamreader, i, j+1): 
     print (', '.join(row)) 

替代（下面的代码是可能的，因为csv.reader接受一个可迭代）：

注意 ：只适用于CSV行不包含换行符的情况。

import itertools 

i, j = 10, 20 
with open(trainFile, 'rt') as csvfile: 
    spamreader = csv.reader(itertools.islice(csvfile, i, j+1), 
          delimiter=' ', quotechar='|') 
    for row in spamreader: 
     print (', '.join(row)) 

Answer 2

使用islice，如：

rows_1_to_50 = itertools.islice(spamreader, 0, 50) 
for row in rows_1_to_50: 
    pass 

Answer 3

使用dropwhile和takewhile

from itertools import takewhile, dropwhile 
trainFile = 'x.1' 
low_lim = 3 
high_lim = 6 
with open(trainFile, 'rt') as csvfile: 
    spamreader = csv.reader(csvfile, delimiter=' ', quotechar='|') 
    g = (x for x in enumerate(spamreader, 1)) 
    g = dropwhile(lambda x: x[0] < low_lim, g) 
    g = takewhile(lambda x: x[0] <= high_lim, g) 
    for row in g: 
     print (', '.join(row[1]))