Question

I have a simple function that sorts a dictionary:

data = inputfile.readlines()
lineData = sorted(data, key=len, reverse=True)[:3]

Printing the output:

print sorted(data, key=len, reverse=True)[:3]

generates the expected result, however writing to file:

outputfile.writelines sorted(data, key=len, reverse=True)[:3]

generates nothing. How can I write the output to the text file (outputfile)?
The complete code is as follows:

import sys, string
inputfilenames, outputfilename = sys.argv[1:-1], sys.argv[-1]


def do_something_with_input(inputfile):
    data = inputfile.readlines()
    print sorted(data, key=len, reverse=True)[:3]
    print sys.path[0]+"/"+ outputfilename


def write_results(outputfile):
    data = inputfile.readlines()
    outputfile.writelines(sorted(data, key=len, reverse=True)[:3])

for inputfilename in inputfilenames:
    inputfile = open(inputfilename, "r")
    do_something_with_input(inputfile)
    outputfile = open(outputfilename, "w")
    write_results(outputfile)

Answer 1

writelines is a method, you need to call it:

outputfile.writelines(sorted(data, key=len, reverse=True)[:3])

ETA
Function open provides file handle which could be iterated over once. You do it in your do_something_with_input function, after the inputfile iterated over, iterator is exhausted. Which means any further iterations, such as done in your write_results functions would yield an empty sequence. That’s why nothing is written to the output file. Basically, it is equivalent to:

>>> a = (i for i in range(2))
>>> list(a)
[0, 1]
>>> list(a)
[]

What you need to do is store the output of the sorted(...) and then write it to the file, not try to generate it again.