python - 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()

Answer 1

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))