Takewhile lambda 函数无法识别字符串

Question

所以我在文件的开头有一个评论部分。我想要的是要拉出以“# Description:”开头的行。但由于某种原因我不明白，它不起作用。输入“#”得到我所期望的结果，“# NOTE”也是如此，但是“# Description:”甚至“# D”似乎 return 什么都没有。有人可以帮我理解吗？

这是我文件的评论部分：

# NOTE: successive whitespace characters treated as single delimiter
# NOTE: all lines beginning with '#' treated as comments
# NOTE: Description must come after '# Description: ' to be recognized
#
# Description: High dispersion optics with O-16 (4+) at 6 MeV/nucleon. Provided by <first, last> on <datetime>.
#
#

这是我使用的代码：

from itertools import takewhile
with open(pathname, 'r') as fobj:
    # takewhile returns an iterator over all the lines
    # that start with the comment string
    headiter = takewhile(lambda s: s.startswith('# Description: '), fobj)
    description = list(headiter)

Answer 1

takewhile 将保留迭代器中的元素，直到条件为 False。在您的情况下，条件在开始时为 False，仅在第三行变为 True。

您想使用 dropwhile 和 next:

from itertools import dropwhile
with open(pathname, 'r') as fobj:
    # dropping lines until they don't start with "# Description:"
    headiter = dropwhile(lambda s: not s.startswith('# Description: '), fobj)
    # getting next element
    description = next(headiter)

输出：

'# Description: High dispersion optics with O-16 (4+) at 6 MeV/nucleon. Provided by <first, last> on <datetime>.'

Takewhile lambda 函数无法识别字符串

Takewhile lambda function not recognizing string

python

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