KeyError
happens in compute_cluster()
in a child process and p.map()
reraises it for you in the parent:
from multiprocessing import Pool
def f(args):
d = {}
d[0] # <-- raises KeyError
if __name__=="__main__":
p = Pool()
p.map(f, [None])
Output
Traceback (most recent call last):
File "raise-exception-in-child.py", line 9, in <module>
p.map(f, [None])
File "/usr/lib/python2.7/multiprocessing/pool.py", line 227, in map
return self.map_async(func, iterable, chunksize).get()
File "/usr/lib/python2.7/multiprocessing/pool.py", line 528, in get
raise self._value
KeyError: 0
To see the full traceback, catch the exception in the child process:
import logging
from multiprocessing import Pool
def f(args):
d = {}
d[0] # <-- raises KeyError
def f_mp(args):
try:
return f(args)
except Exception:
logging.exception("f(%r) failed" % (args,))
if __name__=="__main__":
p = Pool()
p.map(f_mp, [None])
Output
ERROR:root:f(None) failed
Traceback (most recent call last):
File "raise-exception-in-child.py", line 10, in f_mp
return f(args)
File "raise-exception-in-child.py", line 6, in f
d[0] # <-- raises KeyError
KeyError: 0
It shows that d[0]
caused the exception.