Question

I’m beginning my adventure with regular expressions.
I’m interested in splitting specially formatted strings. If a letter is not inside parentheses it should become a different element of output list. Letters grouped inside parentheses should be put together.

Samples:

my string => wanted list

• "ab(hpl)x" => ['a', 'b', 'hpl', 'x']
• "(pck)(kx)(sd)" => ['pck', 'kx', 'sd']
• "(kx)kxx(kd)" => ['kx', 'k', 'x', 'x', 'kd']
• "fghk" => ['f', 'g', 'h', 'k']

How can it be achieved with regular expressions and re.split?
Thanks in advance for your help.

Answer 1

This cannot be done with re.split, as it would require splitting on zero length matches.

From http://docs.python.org/library/re.html#re.split:

Note that split will never split a string on an empty pattern match.

Here is an alternative:

re.findall(r'(\w+(?=\))|\w)', your_string)

And an example:

>>> for s in ("ab(hpl)x", "(pck)(kx)(sd)", "(kx)kxx(kd)", "fghk"):
...     print s, " => ", re.findall(r'(\w+(?=\))|\w)', s)
... 
ab(hpl)x  =>  ['a', 'b', 'hpl', 'x']
(pck)(kx)(sd)  =>  ['pck', 'kx', 'sd']
(kx)kxx(kd)  =>  ['kx', 'k', 'x', 'x', 'kd']
fghk  =>  ['f', 'g', 'h', 'k']