如何使用正则表达式验证字符串格式

Question

Let's say I have a string that looks something like:

first_string = "(white cats || 'dogs) && ($1,000 || $500-$900' || 1,000+)"

And I replace each word with the text "replace" by doing:

new_string = re.sub(r'[\w$\-+,][\w$\-+,\t ]*[\w$\-+,]|[\w$\-+,],', "replace", first_string, flags=re.IGNORECASE)

And I get out:

new_string = "(replace || replace) && (replace || replace || replace)"

This works fine. But I'd like to validate that new_string has a particular format.

For example, is there a way using a regex, to make sure that new_string fits the above general format where:

• There are always sets of parens, separated by an &&
• Each paren set contains strings separated by ||
• Where the number of strings in each paren set and the number of paren sets could vary?

Answer 1

Not used regex.

def is_valid(s):
    def surrounded_by_parens(s, next_validation):
        s = s.strip()
        return s.startswith('(') and s.endswith(')') and next_validation(s[1:-1])
    def separated_by_bars(s):
        return all(x.strip() == 'replace' for x in s.split('||'))
    return all(surrounded_by_parens(x, separated_by_bars) for x in s.split('&&'))

assert is_valid("(replace || replace) && (replace || replace || replace)")
assert is_valid("(replace || replace)")
assert not is_valid("(replace replace) && (replace || replace || replace)")
assert not is_valid("(replace || replace) (replace || replace || replace)")

Answer 2

It is always possible to make regex match any set of configurations or formats you want it to. However some of the strings required to match a set of formats are incredibly long. This one isn't too bad:

re.match(r"\( \w+ (\|\| \w+ )*\)( && \( \w+ (\|\| \w+ )*\))*$", new_string)

This will match:

( replace )
( replace || replace || replace )
( replace || replace ) && ( replace )
( replace || replace ) && ( replace || replace ) && ( replace || replace )

Answer 3

You can check your string structure with this pattern:

^(?:(?:^|\s*[&|]{2}\s*)\([^|)]+(?:\s*\|\|\s*[^|)]+)*\))*$

if && can be inside parenthesis too, you can use:

^(?:(?:^|\s*[&|]{2}\s*)\([^&|)]+(?:\s*[&|]{2}\s*[^&|)]+)*\))*$

If your replacement pattern is good you don't need to check if the parent and the "child" have the same structure.

Notice: if you want to allow void parenthesis, replace all the + quantifiers by *

Answer 4

Description

This regex will match the described foramt (replace || replace) && (replace || replace || replace) where:

• There are always sets of parens, separated by an &&
• Each paren set contains strings separated by ||
• Where the number of strings in each paren set and the number of paren sets could vary?

^(?:(?:&&|^)\\s*\\((?:(?:\\|\\|\\s*)?\\S+\\s*(?=\\|\\||\\)))+\\)\\s*(?=(?:&&|$)))+

Input text:

(Areplace || replace) && (replace || replace || replace)
(Breplace || replace) fda && (replace || replace || replace)
(Creplace || replace) && (replace || replace || replace) && (Creplace || replace) 
(whitecats || 'dogs) && ($1,000 || $500-$900' || 1,000+)

Matches

[0] => (Areplace || replace) && (replace || replace || replace)
[1] => (Creplace || replace) && (replace || replace || replace) && (Creplace || replace) 
[2] => (whitecats || 'dogs) && ($1,000 || $500-$900' || 1,000+)