Unlike its cousins Perl and Ruby, Python has no literal syntax for regular expressions. Whereas one can express the sheep language /baa+/ with a simple forward-slashed literal in Perl and Ruby, in Python one has to compile them using the function re.compile, which produces objects of type re.Pattern. Such objects have various methods for string matching.
sheep = re.compile(r"baa+")
assert sheep.match("baaaaaaaa")
Except, one doesn’t actually have to compile regular expressions at all, as the documentation explains:
Note: The compiled versions of the most recent patterns passed to
re.compile()and the module-level matching functions are cached, so programs that use only a few regular expressions at a time needn’t worry about compiling regular expressions.
What this means is that in the vast majority of cases, re.compile is otiose (i.e., unnecessary). One can just define expression strings, and pass them to the equivalent module-level functions rather than using the methods of re.Pattern objects.
sheep = r"baa+" assert re.match(sheep, "baaaaaaaa")
This, I would argue, is slightly easier to read, and certainly no slower. It also makes typing a bit more convenient since str is easier to type than re.Pattern.
Now, I am sure there is some usage pattern which would favor explicit re.compile, but I have not encountered one in code worth profiling.