[英]Find which lines in a file contain certain characters
Is there a way to find out if a string contains any one of the characters in a set with python? 有没有办法找出一个字符串是否包含一组python中的任何一个字符?
It's straightforward to do it with a single character, but I need to check and see if a string contains any one of a set of bad characters. 使用单个字符执行此操作非常简单,但我需要检查并查看字符串是否包含任何一组错误字符。
Specifically, suppose I have a string: 具体来说,假设我有一个字符串:
s = 'amanaplanacanalpanama~012345'
and I want to see if the string contains any vowels: 我想看看字符串是否包含任何元音:
bad_chars = 'aeiou'
and do this in a for loop for each line in a file: 并在文件中每一行的for循环中执行此操作:
if [any one or more of the bad_chars] in s:
do something
I am scanning a large file so if there is a faster method to this, that would be ideal. 我正在扫描一个大文件,所以如果有更快的方法,这将是理想的。 Also, not every bad character has to be checked---so long as one is encountered that is enough to end the search. 此外,不是每个坏人都必须被检查---只要遇到一个足以结束搜索的人。
I'm not sure if there is a builtin function or easy way to implement this, but I haven't come across anything yet. 我不确定是否有内置函数或简单的方法来实现它,但我还没有遇到过任何问题。 Any pointers would be much appreciated! 任何指针将非常感谢!
any((c in badChars) for c in yourString)
or 要么
any((c in yourString) for c in badChars) # extensionally equivalent, slower
or 要么
set(yourString) & set(badChars) # extensionally equivalent, slower
"so long as one is encountered that is enough to end the search." “只要遇到一个足以结束搜索的人。” - This will be true if you use the first method. - 如果您使用第一种方法,则会出现这种情况。
You say you are concerned with performance: performance should not be an issue unless you are dealing with a huge amount of data. 你说你关心的是性能:除非你处理大量数据,否则性能不应成为问题。 If you encounter issues, you can try: 如果遇到问题,可以尝试:
Regexes 正则表达式
edit Previously I had written a section here on using regexes, via the re
module, programatically generating a regex that consisted of a single character-class [...]
and using .finditer
, with the caveat that putting a simple backslash before everything might not work correctly. 编辑以前我在这里编写了一个关于使用正则表达式的部分,通过re
模块,以编程方式生成由单个字符类[...]
和.finditer
组成的正则表达式,并注意在所有内容之前放置一个简单的反斜杠不正常。 Indeed, after testing it, that is the case, and I would definitely not recommend this method. 事实上,在测试之后,就是这种情况,我绝对不会推荐这种方法。 Using this would require reverse engineering the entire (slightly complex) sub-grammar of regex character classes (eg you might have characters like \\
followed by w
, like ]
or [
, or like -
, and merely escaping some like \\w
may give it a new meaning). 使用这需要逆向工程的整个(稍微复杂)的正则表达式字符类的子语法(例如,你可能有这样的字符\\
之后w
,像]
或[
,或类似-
而只是逃避一些像\\w
可以给它新意义)。
Sets 集
Depending on whether the str.__contains__
operation is O(1) or O(N), it may be justifiable to first convert your text/lines into a set to ensure the in
operation is O(1), if you have many badChars: 根据是否在str.__contains__
操作是O(1)或O(N),它可能是有道理的文本/线先转换成一组,以确保in
操作O(1),如果你有很多badChars:
badCharSet = set(badChars)
any((c in badChars) for c in yourString)
(it may be possible to make that a one-liner any((c in set(yourString)) for c in badChars)
, depending on how smart the python compiler is) (根据python编译器的智能程度,可能可以为any((c in set(yourString)) for c in badChars)
)
Do you really need to do this line-by-line? 你真的需要逐行吗?
It may be faster to do this once for the entire file O(#badchars), than once for every line in the file O(#lines*#badchars), though the asymptotic constants may be such that it won't matter. 对于整个文件O(#badchars)执行此操作可能更快一次,而对于文件O中的每一行(#lines * #badchars)执行此操作可能更快,尽管渐近常量可能无关紧要。
Use python's any
function. 使用python的any
函数。
if any((bad_char in my_string) for bad_char in bad_chars):
# do something
This should be very efficient and clear. 这应该非常有效和清晰。 It uses sets: 它使用集合:
#!/usr/bin/python
bad_chars = set('aeiou')
with open('/etc/passwd', 'r') as file_:
file_string = file_.read()
file_chars = set(file_string)
if file_chars & bad_chars:
print('found something bad')
This regular expression is twice as fast as any
with my minimal testing. 这个正则表达式快两倍, any
与我的最小的测试。 You should try it with your own data. 您应该使用自己的数据进行尝试。
r = re.compile('[aeiou]')
if r.search(s):
# do something
The following Python code should print out any character in bad_chars if it exists in s: 以下Python代码应打印出bad_chars中的任何字符(如果它存在于s中):
for i in vowels:
if i in your charset:
#do_something
You could also use the python in-built any using an example like this: 您也可以使用这样的示例使用内置的python:
>>> any(e for e in bad_chars if e in s)
True
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