Python-why does the 'preg' of PHP require regular expressions with delimiters?

Is it because I learned from Perl? However, Perl is a language embedded with regular expressions. It is natural to use separators to indicate regular expressions. Since PHP uses preg functions, why do I need separators? Function processing is also used in Python (provided by the re module) without separators. {Code...} Haskel... is it because of learning from Perl? However, Perl is a language embedded with regular expressions. It is natural to use separators to indicate regular expressions. PHP is used pregWhy do you need separators for Series function processing?

In Python, function processing is also used (reModule), no separator is required.

pattern = re.compile("foo")

In HaskellText.Regex.PosixYou do not need to use separators.

"my left foot" =~ "foo" :: Bool

Interestingly, PHP 5.3 is obsolete.eregSeries functions do not contain delimiters:

eregi("(ozilla.[23]|MSIE.3)", $_SERVER["HTTP_USER_AGENT"]);

SopregWhen designing a series of functions as pattern, you need to add delimiters. What is the purpose?

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Is it because I learned from Perl? However, Perl is a language embedded with regular expressions. It is natural to use separators to indicate regular expressions. PHP is usedpregWhy do you need separators for Series function processing?

In Python, function processing is also used (reModule), no separator is required.

pattern = re.compile("foo")

In HaskellText.Regex.PosixYou do not need to use separators.

"my left foot" =~ "foo" :: Bool

Interestingly, PHP 5.3 is obsolete.eregSeries functions do not contain delimiters:

eregi("(ozilla.[23]|MSIE.3)", $_SERVER["HTTP_USER_AGENT"]);

SopregWhen designing a series of functions as pattern, you need to add delimiters. What is the purpose?

Some pattern modifiers can be added with separators.m,u,i,sAnd so on. How can I add a separator without it? AndpregThe series followsPCRESeries, so followPCRESome basic rules,POSIXDo not use separators. In additionpregSeries andperlThere are some differences, so it should not beperlLearn it.

References:
Differences between PCRE and perl
Differences between PCRE and POSIX Regular Expressions
Available pattern modifiers in Regular Expressions