如何打开文件并找到最长行的长度并打印出来

Question

我到目前为止做了这些，但长度函数没有正常工作。

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

试试这个：

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()

编辑：添加了 main() 函数。

Answer 2

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

输出结果：

This Should Be Largest Line

作为一个函数：

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")

还有另一种方法，你需要把这个放在一个try/catch里，以处理各种问题（比如空文件等）。

def get_longest_line(filename):
    mydict = {}

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

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

你还需要决定当有两条“获胜”的行长度相等时该怎么办？选择第一条还是最后一条？前面的函数会返回第一条，后面的函数会返回最后一条。文件内容包括：

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

更新

你原始帖子中的评论：

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"

让我觉得你打算扫描文件，先找出每行的长度，然后计算ASCII值的总和，再统计单词数量。其实最好是一次性读取文件，然后从中提取你需要的数据。

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

这个函数会返回一个列表，包含文件中每一行的信息，格式为：行内容, 行长度, 行的ASCII总和, 行的单词数量

可以这样使用：

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)

输出结果：

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

你可以像这样把它和Steef的解决方案结合起来：

>>> 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)

Answer 3

适用于 Python 2.5 到 2.7.12 版本

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

适用于 Python 3 及更高版本

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