import warnings
import sys

warning_emitted = False
warning_allowed = False
warning_expected = False

def showwarning(*args):
	global warning_emitted
	old_showwarning(*args)
	warning_emitted = True

old_showwarning = warnings.showwarning
warnings.showwarning = showwarning

print >> sys.stderr, "*** Warnings are initially allowed"

def forbid_warnings():
	global warning_allowed
	global warning_emitted
	warning_allowed = False
	warning_emitted = False
	print >> sys.stderr
	print >> sys.stderr, "*** Warnings are now forbidden"

def expect_warnings():
	global warning_expected
	global warning_emitted
	warning_expected = True
	warning_emitted = False
	print >> sys.stderr
	print >> sys.stderr, "*** A warning is now expected"

def allow_warnings():
	__tracebackhide__ = True
	global warning_emitted
	global warning_allowed 
	global warning_expected
	assert (not warning_emitted or warning_allowed), "Warning not expected"
	assert (warning_emitted or not warning_expected), "Warning expected"
	warning_emitted = False
	warning_allowed = True
	warning_expected = False
	print >> sys.stderr
	print >> sys.stderr, "*** Warnings are now allowed"