import threading
import warnings 
import time

class MyThread(threading.Thread):
  def run(self):
    with warnings.catch_warnings(True) as self.warninglist:
      for i in range(10):
        # warnings.warn("%s-w%d" % (self.name, i))
        warnings.warn(self.name)
        time.sleep(0.1)

print "warnings.showwarning=%s" % warnings.showwarning
warnings.simplefilter("always")
t1 = MyThread(name="Thread1")
t2 = MyThread(name="Thread2")
t1.start()
time.sleep(0.5)
t2.start()
t1.join()
t2.join()

# both lists should contain 10 items, all of them equal
print "%s catched %d warnings: %s" % (t1.name, len(t1.warninglist), [str(w.message) for w in t1.warninglist])
print "%s catched %d warnings: %s" % (t2.name, len(t2.warninglist), [str(w.message) for w in t2.warninglist])

# keep a reference to the first thread warning list - the thread is dead by now
warninglist = t1.warninglist
assert not t1.is_alive()
del t1
del t2
print "last warning recorded=%s" % warninglist[-1].message

# this warning should appear on console, but is still catched into t1.warninglist
warnings.warn("This should not be catched!")
print "after another warn call, last warning recorded=%s" % warninglist[-1].message

# warnings.showwarning should be the original function by now, but isn't
print "warnings.showwarning=%s" % warnings.showwarning

"""
Output:

warnings.showwarning=<function _show_warning at 0x00ACFBF0>
error-warnings.py:10: UserWarning: Thread2
  warnings.warn(self.name)
error-warnings.py:10: UserWarning: Thread2
  warnings.warn(self.name)
error-warnings.py:10: UserWarning: Thread2
  warnings.warn(self.name)
error-warnings.py:10: UserWarning: Thread2
  warnings.warn(self.name)
Thread1 catched 5 warnings: ['Thread1', 'Thread1', 'Thread1', 'Thread1', 'Thread
1']
Thread2 catched 11 warnings: ['Thread2', 'Thread1', 'Thread2', 'Thread1', 'Threa
d2', 'Thread1', 'Thread2', 'Thread1', 'Thread2', 'Thread1', 'Thread2']
last warning recorded=Thread1
after another warn call, last warning recorded=This should not be catched!
warnings.showwarning=<function showwarning at 0x00B9EDF0>
"""