1 class C: 2 def c(self): 3 return 1 4 5 class D(C): 6 def d(self): 7 return 3 8 9 a = 4 10 l = [] 11 12 def f(x): 13 14 # Test global mutation. 15 16 l.append(x.c()) 17 18 # Test function initialisation. 19 20 def g(y, x=x): # x must be introduced as default here 21 if y: 22 x = D() 23 return x.d(), y, a # UnboundLocalError in Python (if y is a false value) 24 25 return g 26 27 # Provide a default instance for a function to be obtained. 28 29 fn = f(C()) 30 print l # [1] 31 print fn # __main__.f.$l0 32 try: 33 print fn(2) # should fail due to g requiring an object providing d 34 except TypeError: 35 print "fn(2): fn initialised with an inappropriate object" 36 37 try: 38 print fn(0) # should fail due to g requiring an object providing d 39 except TypeError: 40 print "fn(0): fn initialised with an inappropriate object" 41 42 # Override the default when calling the function. 43 44 print fn(2, D()) # (3, 2, 4) 45 print fn(0, D()) # (3, 0, 4) 46 47 # Provide a more suitable default instance for the function. 48 49 fn = f(D()) 50 print l # [1, 1] 51 print fn(2) # (3, 2, 4) 52 print fn(0) # (3, 0, 4) 53 print fn(0, D()) # (3, 0, 4) 54 55 # Override with an unsuitable object even though it would be ignored. 56 57 try: 58 print fn(1, C()) 59 except TypeError: 60 print "fn(1, C()): an unsuitable argument was given." 61 62 # Override with an unsuitable object. 63 64 try: 65 print fn(0, C()) 66 except TypeError: 67 print "fn(0, C()): an unsuitable argument was given."
