when you add "x" into list "version"(change to tuple) at return statement if x is NOT digits, this will cause type error later when you compare tuple (1,12,'1rc1) to tuple (1,12,0). Two possible solution.

    Use tuple of string.
    Change version.append(int(x))
    to version.append(x)
    Comparison using tuple of strings.
    Change tuple (1,12,0) to ('1', '12', '0') etc.
    A lot of changes.
    Simple fix. Extract numeric portion of x if x contains letters using regular expression. Comparison keeps the same.

Hope somebody will merge my fix into next release because I'm NOT a contributor.
...
import re
...
def _parse_version(version_string):
version = []
for x in version_string.split('.'):
try:
version.append(int(x))
except ValueError:
# x may be of the form dev-1ea1592
# version.append(x)
digits=re.match(r'^(\d)+\D',x)
if digits:
version.append(int(digits.group(1)))
else:
# use 0 if no leading digits found
version.append(0)
return tuple(version)

Test environment:
Python 3.4
Numpy 1.12.1rc1
sklearn 0.18.1