Precompiled regular expressions slower?

Cezary Biernacki cezary at bigfoot.com
Wed Feb 27 07:23:23 CET 2002


Huaiyu Zhu wrote:

> On Tue, 26 Feb 2002 11:17:53 -0500, Peter Bienstman <pbienst at mit.edu> wrote:
> 
> Yes.  Use re1.search(line) instead.  
> 
> The times of the following three tests are:
> 1.94322395325   # search(string, string)
> 2.62431204319   # search(re_obj, string)
> 0.667925000191  # re_obj.search(string)
> 
> Someone care to explain why the second ends up slower than the first?

Look at _compile in sre.py (the standard library):

def _compile(*key):
     # internal: compile pattern
     p = _cache.get(key)
     if p is not None:
         return p
     pattern, flags = key
     if type(pattern) not in sre_compile.STRING_TYPES:
         return pattern
     try:
         p = sre_compile.compile(pattern, flags)
     except error, v:
         raise error, v # invalid expression
     if len(_cache) >= _MAXCACHE:
         _cache.clear()
     _cache[key] = p
     return p

In first case pattern is found in "_cache" and directly returned.
In second case "if type(pattern) not in sre_compile.STRING_TYPES" must 
be also tested.


--
CB




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