在python中排序文本文件的内容后文件中的空白行

Question

我有这个小脚本来排序文本文件的内容

# The built-in function `open` opens a file and returns a file object.

# Read mode opens a file for reading only.
try:
    f = open("tracks.txt", "r")


    try:
        # Read the entire contents of a file at once.
       # string = f.read() 
        # OR read one line at a time.
        #line = f.readline()
        # OR read all the lines into a list.
        lines = f.readlines()
        lines.sort()
        f.close()
        f = open('tracks.txt', 'w')
        f.writelines(lines) # Write a sequence of strings to a file
    finally:
        f.close()
except IOError:
    pass

唯一的问题是文本每次被分类时都会显示在文本文件的底部...

我认为它也排除了空白行......任何人都知道为什么？

也许你可以建议一些如何避免这种情况发生的提示？

提前致谢

Answer 1

从文本文件读取的"空"行在Python中由仅包含换行符("\n")的字符串表示.您可能还想避免"数据"仅包含空格,制表符等("空白")的行.str.strip()方法允许您检测两种情况(换行符是空格).

f = open("tracks.txt", "r")
# omit empty lines and lines containing only whitespace
lines = [line for line in f if line.strip()]
f.close()
lines.sort()
# now write the output file

Answer 2

这是进行基于测试的开发的绝佳机会(见下文).一些观察:

1. 在下面的示例中,我省略了读取和写入文件的方面.在我看来,这对于这个问题并不重要.

2. 我假设您要删除尾随换行符并省略空行.如果没有,你需要调整.(但是你将拥有断言/确认预期行为的框架.)

3. 我同意上面的chryss,你通常不需要在Python中的try块中反复包装东西.我认为,这是来自Java(它强制它)的反模式.

无论如何,这是测试:

import unittest

def sort_lines(text):
    """Return text sorted by line, remove empty lines and strip trailing whitespace."""
    lines = text.split('\n')
    non_empty = [line.rstrip() for line in lines if line.strip()]
    non_empty.sort()
    return '\n'.join(non_empty)

class SortTest(unittest.TestCase):

  def test(self):
    data_to_sort = """z some stuff
c some other stuff


d more stuff after blank lines
b another line
a the last line"""

    actual = sort_lines(data_to_sort)
    expected = """a the last line
b another line
c some other stuff
d more stuff after blank lines
z some stuff"""

    self.assertEquals(actual, expected, "no match!")

unittest.main()