我在問自己Python3.6是否有類的默認構造函數。所以我寫了一些代碼來測試這個。但是當我開始測試時,我留下了更多的問題。Python是否有類的默認構造函數?
我試圖理解爲什麼myCat建在我的程序的第11行確定,但我無法解釋爲什麼我的程序的第27行要求將自己知道
請,如果你能幫助,請閱讀此Python代碼和輸出......它有道理嗎? 我做了2個文件animal.py和an_test_program.py。
#!/usr/bin/env python3
#animal.py file ==============================
class animal:
name = ""
height = 0
weight = 0
def __init__(self, name, height, weight):
self.name = name
self.height = height
self.weight = weight
def printvars(self):
print(self.name)
print(self.height)
print(self.weight)
#!/usr/bin/env python3
#an_animal_program.py ==============================
import animal as an
#Instantiate a variable of type animal using the special constructor of the class
myDog = an.animal('Capitan', 30, 70)
print('myDog\'s name is ' + myDog.name)
myDog.printvars()
#now play around with Python and discover some things...
#Instantiate a variable of type animal without using the special constructor
myCat = an.animal
print('myCat\'s name is ' + myCat.name)
print('myCat\'s height is ' + "%d" % (myCat.height))
print('myCat\'s weight is ' + "%d" % (myCat.weight))
#notice everything in myCat is empty or zero
#thats because myCat is not initialized with data
#none-the-less myCat is a viable object, otherwise Python would puke out myCat
myCat.name = 'Backstreet'
print('myCat\'s name is ' + myCat.name) # now myCat.name has data in it
#Ouch... this next line produces an error:
#myCat.printvars()
#"an_test_program.py", line 21, in <module>
# myCat.printvars()
#TypeError: printvars() missing 1 required positional argument: 'self'
myCat.printvars(myCat) #ok, I'm rolling with it, but this is wierd !!!
#oh well, enough of the wierdness, see if the myCat var can be
#reinstantiated with an animal class that is correctly constructed
myCat = an.animal('Backstreet', 7, 5)
myCat.printvars()
#I'm trying to understand why myCat constructed ok on line 11
#But I can't explain why line 27 demanded to know itself
#the output is:
# RESTART: an_test_program.py
#myDog's name is Capitan
#Capitan
#30
#70
#myCat's name is
#myCat's height is 0
#myCat's weight is 0
#myCat's name is Backstreet
#Backstreet
#0
#0
#Backstreet
#7
#5
要迂迴,'.__ init__'就是實例_initializer_。實例構造函數被稱爲'.__ new__'。類從'object'繼承'.__ new__'方法,並且通常不需要覆蓋它,雖然這當然是可以的。 –
謝謝。這就說得通了。 – MrEmanLOL
您可能會發現這篇文章有幫助:[關於Python名稱和值的事實和神話](http://nedbatchelder.com/text/names.html),這是由SO老手Ned Batchelder編寫的。另請參閱[其他語言具有「變量」,Python具有「名稱」](http://python.net/~goodger/projects/pycon/2007/idiomatic/handout.html#other-languages-have-variables)簡要總結,用可愛的圖表。 –