仅打印.csv文件中的最后8个条目

Question

I have an input csv file as below,I want to print only the most recent 8 entries..can anyone provide inputs on how to do this?

INPUT:-
trend.csv

['2013-06-25 20:01', '10']
['2013-06-25 20:06', '9']
['2013-06-25 20:06', '8']
['2013-06-26 20:06', '7']
['2013-06-26 20:06', '6']
['2013-06-26 20:06', '5']
['2013-06-26 20:06', '4']
['2013-06-26 20:06', '3']
['2013-06-26 20:06', '2']
['2013-06-26 20:08', '1']

OUTPUT:-
['2013-06-25 20:06', '8']
['2013-06-26 20:06', '7']
['2013-06-26 20:06', '6']
['2013-06-26 20:06', '5']
['2013-06-26 20:06', '4']
['2013-06-26 20:06', '3']
['2013-06-26 20:06', '2']
['2013-06-26 20:08', '1']

Code:

import csv
#Now read the recent 8 entries and print
cr = csv.reader(open("trend.csv","rb"))

for row in cr:  
    #print only the recent most 8 entries
    print row

Answer 1

You can use the tail recipe with a deque with n=8.

This creates a double ended queue where adding an item to the end (right) will efficiently pop off an item at the beginning (the left) to keep the length no more than max length:

>>> from collections import deque
>>> deque(range(10000),8)
deque([9992, 9993, 9994, 9995, 9996, 9997, 9998, 9999], maxlen=8)

The csv.reader object is an iterator. Apply a limited-length deque to the csv reader and you are good to go:

import csv
from collections import deque

with open('/tmp/trend.csv','rb') as fin:
    deq=deque(csv.reader(fin),8)

for sub_list in deq:
    print sub_list

With your 10 line example, this prints:

['2013-06-25 20:06', '8']
['2013-06-26 20:06', '7']
['2013-06-26 20:06', '6']
['2013-06-26 20:06', '5']
['2013-06-26 20:06', '4']
['2013-06-26 20:06', '3']
['2013-06-26 20:06', '2']
['2013-06-26 20:08', '1']

Answer 2

import csv

# Open the file with a "with" statement to provide automatic cleanup
# in case of exceptions.
with open("trend.csv","rb") as file:
    cr = csv.reader(file)
    lines = [row for row in cr]
# Use slice notation and the wonderful fact that python treats
# negative indices intelligently!
for line in lines[-8:]:
    print line

Answer 3

If memory/performance isn't an issue you could just do:

for row in list(cr)[-8:]:  
    print row