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Test Your Knowledge: Answers
- Here’s one way to code the first question’s solution, and its output (albeit with class methods that run too fast to time). The trick lies in replacing nested classes with nested functions, so the self argument is not the decorator’s instance, and assigning the total time to the decorator function itself so it can be fetched later through the original rebound name (see the section State Information Retention Options of this chapter for details—functions support arbitrary attribute attachment, and the function name is an enclosing scope reference in this context).
import time
def timer(label='', trace=True): # On decorator args: retain args
def onDecorator(func): # On @: retain decorated func
def onCall(*args, **kargs): # On calls: call original
start = time.clock() # State is scopes + func attr
result = func(*args, **kargs)
elapsed = time.clock() - start
onCall.alltime += elapsed
if trace:
format = '%s%s: %.5f, %.5f'
values = (label, func.__name__, elapsed, onCall.alltime)
print(format % values)
return result
onCall.alltime = 0
return onCall
return onDecorator
# Test on functions
@timer(trace=True, label='[CCC]==>')
def listcomp(N): # Like listcomp = timer(...)(listcomp)
return [x * 2 for x in range(N)] # listcomp(...) triggers onCall
@timer(trace=True, label='[MMM]==>')
def mapcall(N):
return list(map((lambda x: x * 2), range(N))) # list() for 3.0 views
for func in (listcomp, mapcall):
result = func(5) # Time for this call, all calls, return value
func(5000000)
print(result)
print('allTime = %s\n' % func.alltime) # Total time for all calls
# Test on methods
class Person:
def __init__(self, name, pay):
self.name = name
self.pay = pay
@timer()
def giveRaise(self, percent): # giveRaise = timer()(giveRaise)
self.pay *= (1.0 + percent) # tracer remembers giveRaise
@timer(label='**')
def lastName(self): # lastName = timer(...)(lastName)
return self.name.split()[-1] # alltime per class, not instance
bob = Person('Bob Smith', 50000)
sue = Person('Sue Jones', 100000)
bob.giveRaise(.10)
sue.giveRaise(.20) # runs onCall(sue, .10)
print(bob.pay, sue.pay)
print(bob.lastName(), sue.lastName()) # runs onCall(bob), remembers lastName
print('%.5f %.5f' % (Person.giveRaise.alltime, Person.lastName.alltime))
# Expected output
[CCC]==>listcomp: 0.00002, 0.00002
[CCC]==>listcomp: 1.19636, 1.19638
[0, 2, 4, 6, 8]
allTime = 1.19637775192
[MMM]==>mapcall: 0.00002, 0.00002
[MMM]==>mapcall: 2.29260, 2.29262
[0, 2, 4, 6, 8]
allTime = 2.2926232943
giveRaise: 0.00001, 0.00001
giveRaise: 0.00001, 0.00002
55000.0 120000.0
**lastName: 0.00001, 0.00001
**lastName: 0.00001, 0.00002
Smith Jones
0.00002 0.00002 - The following satisfies the second question—it’s been augmented to return the original class in optimized mode (–O), so attribute accesses don’t incur a speed hit. Really, all I did was add the debug mode test statements and indent the class further to the right. Add operator overloading method redefinitions to the wrapper class if you want to support delegation of these to the subject class in 3.0, too (2.6 routes these through __getattr__, but 3.0 and new-style classes in 2.6 do not).
traceMe = False
def trace(*args):
if traceMe: print('[' + ' '.join(map(str, args)) + ']')
def accessControl(failIf):
def onDecorator(aClass):
if not __debug__:
return aClass
else:
class onInstance:
def __init__(self, *args, **kargs):
self.__wrapped = aClass(*args, **kargs)
def __getattr__(self, attr):
trace('get:', attr)
if failIf(attr):
raise TypeError('private attribute fetch: ' + attr)
else:
return getattr(self.__wrapped, attr)
def __setattr__(self, attr, value):
trace('set:', attr, value)
if attr == '_onInstance__wrapped':
self.__dict__[attr] = value
elif failIf(attr):
raise TypeError('private attribute change: ' + attr)
else:
setattr(self.__wrapped, attr, value)
return onInstance
return onDecorator
def Private(*attributes):
return accessControl(failIf=(lambda attr: attr in attributes))
def Public(*attributes):
return accessControl(failIf=(lambda attr: attr not in attributes))
# Test code: split me off to another file to reuse decorator
@Private('age') # Person = Private('age')(Person)
class Person: # Person = onInstance with state
def __init__(self, name, age):
self.name = name
self.age = age # Inside accesses run normally
X = Person('Bob', 40)
print(X.name) # Outside accesses validated
X.name = 'Sue'
print(X.name)
#print(X.age) # FAILS unles "python -O"
#X.age = 999 # ditto
#print(X.age) # ditto
@Public('name')
class Person:
def __init__(self, name, age):
self.name = name
self.age = age
X = Person('bob', 40) # X is an onInstance
print(X.name) # onInstance embeds Person
X.name = 'Sue'
print(X.name)
#print(X.age) # FAILS unless "python –O main.py"
#X.age = 999 # ditto
#print(X.age) # ditto
