How to open a file and find the longest length of a line and then print it out

Question

Here's is what I have done so far but the length function isn't working.

import string

def main():
    print " This program reads from a file and then prints out the"
    print " line with the longest length the line ,or with the highest sum"
    print " of ASCII values , or the line with the greatest number of words"
    infile = open("30075165.txt","r")
    for line in infile:
        print line
    infile.close()
def length():
    maxlength = 0
    infile = open("30075165.txt","r")
    for line in infile:
        linelength = lengthofline
        if linelength > maxlength:
            #If linelength is greater than maxlength value the new value is linelength
            maxlength = linelength
            linelength = line
    print ,maxlinetext
    infile.close()

Consider explaining WHY it's not working. You will learn a lot from learning to explain why it's not working. — Lennart Regebro, Aug 28 '09 at 05:18

score 32 · Accepted Answer · edited Jun 19 '18 at 21:36

32

For Python 2.5 to 2.7.12

print max(open(your_filename, 'r'), key=len)

For Python 3 and up

print(max(open(your_filename, 'r'), key=len))

edited Jun 19 '18 at 21:36

Nick Silvestri

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1
15

answered Aug 18 '09 at 09:06

Steef

33,059
4
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I like this. I didn't realise you could pass a key arg into max. Now I do. – kjfletch Aug 18 '09 at 09:17

kjfletch · Answer 2 · 2009-08-18T11:00:36.590

large_line = ''
large_line_len = 0
filename = r"C:\tmp\TestFile.txt"

with open(filename, 'r') as f:
    for line in f:
        if len(line) > large_line_len:
            large_line_len = len(line)
            large_line = line

print large_line

output:

This Should Be Largest Line

And as a function:

def get_longest_line(filename):
    large_line = ''
    large_line_len = 0

    with open(filename, 'r') as f:
        for line in f:
            if len(line) > large_line_len:
                large_line_len = len(line)
                large_line = line

    return large_line

print get_longest_line(r"C:\tmp\TestFile.txt")

Here is another way, you would need to wrap this in a try/catch for various problems (empty file, etc).

def get_longest_line(filename):
    mydict = {}

    for line in open(filename, 'r'):
        mydict[len(line)] = line

    return mydict[sorted(mydict)[-1]]

You also need to decide that happens when you have two 'winning' lines with equal length? Pick first or last? The former function will return the first, the latter will return the last. File contains

Small Line
Small Line
Another Small Line
This Should Be Largest Line
Small Line

Update

The comment in your original post:

print " This program reads from a file and then prints out the"
print " line with the longest length the line ,or with the highest sum"
print " of ASCII values , or the line with the greatest number of words"

Makes me think you are going to scan the file for length of lines, then for ascii sum, then for number of words. It would probably be better to read the file once and then extract what data you need from the findings.

def get_file_data(filename):
    def ascii_sum(line):
        return sum([ord(x) for x in line])
    def word_count(line):
        return len(line.split(None))

    filedata = [(line, len(line), ascii_sum(line), word_count(line)) 
                for line in open(filename, 'r')]

    return filedata

This function will return a list of each line of the file in the format: line, line_length, line_ascii_sum, line_word_count

This can be used as so:

afile = r"C:\Tmp\TestFile.txt"

for line, line_len, ascii_sum, word_count in get_file_data(afile):
    print 'Line: %s, Len: %d, Sum: %d, WordCount: %d' % (
        line.strip(), line_len, ascii_sum, word_count)

to output:

Line: Small Line, Len: 11, Sum: 939, WordCount: 2
Line: Small Line, Len: 11, Sum: 939, WordCount: 2
Line: Another Small Line, Len: 19, Sum: 1692, WordCount: 3
Line: This Should Be Largest Line, Len: 28, Sum: 2450, WordCount: 5
Line: Small Line, Len: 11, Sum: 939, WordCount: 2

You can mix this with Steef's solution like so:

>>> afile = r"C:\Tmp\TestFile.txt"
>>> file_data = get_file_data(afile)
>>> max(file_data, key=lambda line: line[1]) # Longest Line
('This Should Be Largest Line\n', 28, 2450, 5)
>>> max(file_data, key=lambda line: line[2]) # Largest ASCII sum
('This Should Be Largest Line\n', 28, 2450, 5)
>>> max(file_data, key=lambda line: line[3]) # Most Words
('This Should Be Largest Line\n', 28, 2450, 5)

This is good code but it isn't working for me the code you have gave me comes up blank? — BForce01, Aug 18 '09 at 12:51
It comes out blank because I have not specified any output. If you want to print output use the print statement. If you want to write it to a file, write it to a file. Would you like to know how to do that too? Would you like me to write a beginners guide to Python for you? — kjfletch, Aug 18 '09 at 13:29

Aamir · Answer 3 · 2009-08-18T09:15:54.210

1

Try this:

def main():
    print " This program reads from a file and then prints out the"
    print " line with the longest length the line ,or with the highest sum"
    print " of ASCII values , or the line with the greatest number of words"
    length()

def length():
    maxlength = 0
    maxlinetext = ""
    infile = open("30075165.txt","r")
    for line in infile:
        linelength = len(line)
        if linelength > maxlength:
            #If linelength is greater than maxlength value the new value is linelength
            maxlength = linelength
            maxlinetext = line
    print maxlinetext
    infile.close()

EDIT: Added main() function.

edited Aug 18 '09 at 09:15

answered Aug 18 '09 at 08:52

Aamir

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This code works but it prints out every line not the max length line – BForce01 Aug 18 '09 at 09:01
No, this should work. You need to take care of indentation and indent the code as it is. Don't change the indentation. Python blocks work on indentation. – Aamir Aug 18 '09 at 09:09
No, BForce, you're code in the main function prints out every line. – Lloyd Powell Aug 18 '09 at 09:10

score 0 · Answer 4 · answered Aug 18 '09 at 08:58

0

linelength = lengthofline # bug?

It should be:

linelength = len(line) # fix

answered Aug 18 '09 at 08:58

Nick Dandoulakis

42,588
16
104
136

score 0 · Answer 5 · answered Aug 18 '09 at 09:06

0

Python might not be the right tool for this job.

$ awk 'length() > n { n = length(); x = $0 } END { print x }' 30075165.txt

answered Aug 18 '09 at 09:06

Steven Huwig

20,015
9
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score 0 · Answer 6 · answered Aug 18 '09 at 09:07

My solution (also works in Python 2.5):

import os.path

def getLongestLineFromFile(fileName):
    longestLine = ""

    if not os.path.exists(fileName):
        raise "File not found"

    file = open(fileName, "r")
    for line in file:
        if len(line) > len(longestLine):
            longestLine = line

    return longestLine


if __name__ == "__main__":
    print getLongestLineFromFile("input.data")

Example "input.data" contents:

111111111
1111111111111111111111
111111111
22222222222222222
4444444444444444444444444444444
444444444444444
5555

How to open a file and find the longest length of a line and then print it out

6 Answers6

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