如何使用python仅打印一行中的某些字符

Question

For example, I have:

a = (b ^ c) || d && e

I want it to print only

^ || &&  

I am new to python. Could someone help me with this?

Answer 1

We can filter out the unwanted characters with filter :

>>> a = "(b ^ c) || d && e"
>>> print(*filter(lambda x: not x.isalpha() and x not in '()', a), sep='')
 ^  ||  &&

Or, if you don't want multiple spaces or leading/trailing spaces:

>>> print(''.join(filter(lambda x: not x.isalpha() and x not in '()', a)).replace('  ',' ').strip())
^ || &&

Answer 2

您可以按不需要的字符组拆分字符串，然后继续连接和去除空间：

' '.join(re.split(r'[\s\d\w()]+', a)).strip() # remove numbers, letters, and whitespace

Answer 3

Edit1

To correct misunderstanding I can suggest use regexp for this.

import re
print(re.sub(r"[^\^|\|\||\&\&]", "", a))

Edit2

Comments for code above.

re.sub() function replaces by second parameter all tokens that match given pattern. Quick training you can pass here regexone.com

That part of code finds all yours symbols using given regex and replaces them by empty string.

r"[^\^|\|\||\&\&]"

That regex has a folowing parts

[^] - that tells find all symbols that not between [ and ]. ^ symbol used for negation.

\\^\\^ - your ^^ symbols shielded using backslashes

\\|\\| - your || symbols

\\&\\& - your && symbols

All of them grouped using "or" statement ( "|" symbol )

In the end you have

^^ | || | && without backslashes tells, find ^^ or || or &&

and in [^ ^^ | || | &&], finds every symbol that not ^^ or || or &&

But if you coding at first time, or you don't know python syntax yet, i recommend you just learn python at simplest examples, and after that learn regex syntax.