Question

我有一个格式为

的文件

_line 1
this is a string on a line
_line 2
this is another string
_line 3
short line

我正在尝试编写一些Python代码来获取其下面字符串长度最长的字符串的_line X标签。你能帮我修改一下我的代码吗？这是我到目前为止所拥有的。

f = open('test.txt', 'r')
print f

read="null"
top_read_line_length="0"
topreadline="null"
for line in f:
    checkifread=line.find('line')
    if checkifread==1:
        print "Read label found"
        #means we are on a read line
        currentread=line
    else:
        #We are on a sequence line for currentread.
        currentlength=len(line)
        print currentlength
    print top_read_line_length

    if int(top_read_line_length) < int(currentlength):
        print topreadline
        topreadline=currentread#now topreadline label is the "_line" string
        topreadlinelength=int(currentlength)
        print topreadline

        #go to next line

print "Done"
print "Longest line is...."
print topreadline

Answer 1

如果你想要的只是文件中最长的一行（就像问题标题所说的那样），那么在现代Python中这一行非常简单：

>>> max(open('test.txt'), key=len)

Answer 2

要获取最长行的标签，请构建标签到行长度的映射

在您的示例数据集中，看起来标签以“_line”开头，紧接着的是相应的行：

label2linelength = {}
for line in open('test.txt'):
    if line.startswith('_line '):
        label = line
    else:
        label2linelength[label] = len(line)
    lastline = line
print max(label2linelength.items(), key=lambda kv: kv[1])

Answer 3

这很容易实现：

data = open('test.txt').readlines()
max_line_pos = data.index(max(data, key=len))
prev_line = data[max_line_pos-1]
print prev_line

Answer 4

我会做类似的事情：

label = None
maxlen = 0
maxstr = ''
maxlabel = None
with open('f.txt') as f:
  for line in f:
    line = line.rstrip()
    if line.startswith('_line'):
      label = line
    elif len(line) > maxlen:
      maxlen = len(line)
      maxstr = line
      maxlabel = label
print maxlabel, maxstr

它比问题陈述更通用，因为它允许每个标签有多行文字。

Answer 5

我详细说明雷蒙德的答案;如果石斑鱼（）在标准库中可用，那么这个答案将再次接近一个oneliner;不幸的是，石斑鱼只在itertools examples.

中定义

我认为你更喜欢这个版本，因为它很实用。我没有测试它的性能，但至少我没有打开文件并寻求两次，也没有将整个内容保存在内存中。

from itertools import izip_longest
def grouper(n, iterable, fillvalue=None):
    "grouper(3, 'ABCDEFG', 'x') --> ABC DEF Gxx"
    args = [iter(iterable)] * n
    return izip_longest(fillvalue=fillvalue, *args)

max( grouper(2, open("test.txt")), key=lambda x:len(x[1]))[0]

Answer 6

另一个简洁的变体：

from itertools import imap, izip
from operator import itemgetter
with open("a.py") as f:
    res = max(izip(f, imap(len, f)), key=itemgetter(1))[0]

这会将所有其他行视为标签。

Answer 7

这是我的。它适用于这里的一些其他答案会失败的地方，例如：像

这样的输入文件

_line 1
abc
_line 2
defg
_line 3
hij

但它确实依赖于文件的格式，就像你说的那样。

with open('test.txt') as f:
  spam = f.readlines()

labels = spam[0::2]
lines = spam[1::2]

d = dict(zip(labels, lines))

longest_lines_label = max(d, key=lambda x: len(d[x]))

print "Longest line is...."
print longest_lines_label, d[longest_lines_label]

Answer 8

如果你确定数据是正确的并且不需要任何错误处理，那么应该完成这项工作：

lines = open('test.txt', 'r').readlines()
print max([(len(lines[i+1]), lines[i])
           for i in xrange(0, len(lines), 2)])[1].strip()

Answer 9

这是一个awk程序，它将执行此操作：

BEGIN { best=""; best_length=0; current=""; }
/^_/ { current=$0; }
/^[^_]/ { if(length($0) > best_length) { best=current; best_length=length($0); }}
END { print "Longest line: "best" with length: "best_length }

（我比以下python版本更喜欢它，它更贴切地回答了你的问题....）

best = ""
best_length = 0
current = ""
for line in f:  #( assumes f = open(...) from your code )
  if line[:5] == '_line':
    current = line.strip()
    continue
  else:
    if len(line) > best_length:
      best = current
      best_length = len(line.strip())
print "Longest line is: %s with length: %d" % (best,best_length)

Answer 10

这个很短，即使你在每个标签后有多行文字

也行

content = list(open("test.txt"))
longest = content.index(max(content, key=len))
label = [ x for x in content[0:longest] if x.startswith("_line") ][-1]
print label.replace("_line ","")

Answer 11

这是另一种方式：

import re, mmap

with open("test.txt", "rb") as f:
    mm = mmap.mmap(f.fileno(), 0, mmap.MAP_PRIVATE, mmap.PROT_READ)
    print max(re.finditer(r'_line (\d+)\n(.*)', mm),
              key=lambda m: len(m.group(2))).group(1)

Answer 12

这是您的代码，已修复：

f = open('test.txt', 'r')
print f

read = None
top_read_line_length = 0
topreadline = None
currentlength = 0
label_line = True
for line in f:  
    if label_line:
        label_line = False
        print "label line", line
        #means we are on a read line
        currentread = line
    else:
        label_line = True
        #We are on a sequence line for currentread.
        currentlength = len(line)
        print 'cl', currentlength
    print top_read_line_length

    if top_read_line_length < currentlength:
        print 'trl', topreadline
        topreadline = currentread #now topreadline label is the "_line" string
        top_read_line_length = currentlength
        print 'trl', topreadline

        #go to next line

print "Done"
print "Longest line is...."
print topreadline

我添加了label_line布尔值来在标签行和数据行之间来回切换，但重要的部分是：

在您的打印行上放置足够的信息以查看正在发生的事情;和
与您的变量名称一致

问题发生在上一个if套件中 - 您正在检查top_read_line_length但是正在设置topreadlinelength（没有下划线）。

查找文件中最长行之前的标签

12 个答案: