Print in Reverse Order Python

Question

f = urlopen ('http://ichart.finance.yahoo.com/table.csv?s=AAPL&d=4&e=29&f=2014&g=d&a=8&b=22&c=1981&ignore=.csv')
sys.stdout = open('output.csv', 'w')
p = f.read()
print p
f.close

This successfully opens (or creates) a file called output.csv and outputs the lines from the downloaded file into this local csv. How would I reverse the order that the lines are printed in?

why am I getting downvoted. Is there a problem with my question? — Apollo, May 29 '14 at 16:40
@Apollo no, this is just a duplicate of so many questions that it's painful. — Adam Smith, May 29 '14 at 16:41
A search of "print lines in file in reverse order python" turns this [answer](http://stackoverflow.com/a/2301792/2297365) up. — huu, May 29 '14 at 16:42

score 5 · Answer 1 · answered May 29 '14 at 16:38

5

You can use the readlines() method to get a list of lines instead of the single string you get from read(). This list can be reversed using the reversed() built-in:

for line in reversed(f.readlines()):
    print line

answered May 29 '14 at 16:38

Sven Marnach

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I think you meant `print line`. – huu May 29 '14 at 16:39

Antti Haapala -- Слава Україні · Accepted Answer · 2014-05-30T15:00:50.917

3

If there is a header in the input, you might want to print the header first; followed by the remaining lines.

f = urlopen ('http://ichart.finance.yahoo.com/table.csv?s=AAPL&d=4&e=29&f=2014&g=d&a=8&b=22&c=1981&ignore=.csv')
with open('output.csv', 'w') as out:
    # print header first
    out.write(f.readline())

    # then print reversed lines
    for line in reversed(f.readlines()):
        out.write(line)

f.close()  # !!!

edited May 30 '14 at 15:00

answered May 29 '14 at 16:41

Antti Haapala -- Слава Україні

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Argument to `reversed` should be a sequence. – falsetru May 29 '14 at 16:42
indeed, forgot that (bleh). – Antti Haapala -- Слава Україні May 29 '14 at 16:43
N.B. this will print the header first and last :) – Adam Smith May 29 '14 at 16:43
`TooManyErrorsError` :D – Antti Haapala -- Слава Україні May 29 '14 at 16:46
@AdamSmith nope, it won't (at least not in this version) – Antti Haapala -- Слава Україні May 29 '14 at 16:47
1

You don't need to close `out`. – huu May 29 '14 at 16:48
@AnttiHaapala does `readline` actually move the seek? I assumed it did not but I could be wrong :). I would do `f_data = f.readlines(); for line in [f_data[0]] + list(reversed(f_data[1:])): out.write(line)` but that's WAY uglier than yours if that works :D – Adam Smith May 29 '14 at 16:48
@AnttiHaapala this is actually something I was struggling to do. Thanks – Apollo May 30 '14 at 14:47
@HuuNguyen yeah, had that close dangling there, removed. too bad urlopen does not return something with context mgr in py2. – Antti Haapala -- Слава Україні May 30 '14 at 15:01

Print in Reverse Order Python

2 Answers2