how could i distinguish default-parameter method in python

Asked Dec 25 '13 at 06:06

Active Dec 25 '13 at 08:59

Viewed 46 times

recently,i am learn python.i met a problem when i readed this book named The_Python_Tutorial.it's about how to distinguish the method with default parameter.i googled and read other books while i try to solve it,but i failed.if you can help me,plz. here is my problem:

  def f(a,L=[]):
        L.append(a)
        return L
    print(f(1))
    print(f(2))
    print(f(3))

it shows

[1]
[1,2]
[1,2,3]

so i changed another way

 def g(a,L=None):
            if L is None:
                L=[]
            L.append(a)
            return L
     print (g(1))
     print (g(2))
     print (g(3))

it just shows

[1]
[2]
[3]

how it happens?too weird.all i want to know is that why diff betwween this two method and sommeone can explain it. thanks.

edited Dec 25 '13 at 08:59

asked Dec 25 '13 at 06:06

Mark

Nope. It works fine for me... Please check the output again. – thefourtheye Dec 25 '13 at 06:08
@Blender: the "Least Astonishment" question is related. But how is it a duplicate? How do you explain `[1] [1] [1]` output? – jfs Dec 25 '13 at 06:08
@Mark: [edit] your question and fix the indentation of your Python code. Indentation is significant in Python. – jfs Dec 25 '13 at 06:09
@J.F.Sebastian: I couldn't reproduce that output in three Python versions, so I'm assuming it's a bug with OP's test code. – Blender Dec 25 '13 at 06:10
@Blender: exactly my point. Instead of closing the question as a duplicate, the error should be pointed out. – jfs Dec 25 '13 at 06:11
@thefourtheye: I checked I am getting similar result as depicted in OP – MaNKuR Dec 25 '13 at 06:13
@MaNKuR Could you please show in ideone.com? This is what I tried http://ideone.com/1crw1l – thefourtheye Dec 25 '13 at 06:14
@thefourtheye : Here is the result http://ideone.com/wARWlJ – MaNKuR Dec 25 '13 at 06:18
if I understand OP correctly, he is asking the diff between method `f()` and `g()` why its getting different result. – MaNKuR Dec 25 '13 at 06:22
@MaNKuR: it doesn't reproduce OP's case. In your code `g(n)` leads to `[n]` but OP shows `g(n)` -> `[1]`. – jfs Dec 25 '13 at 06:32
oh yes.... I missed this :) – MaNKuR Dec 25 '13 at 06:39
@MaNKuR yes,just like you say,i just want to know the diff between this two method and why? – Mark Dec 25 '13 at 08:56
thanks to everone,i got my answer. – Mark Dec 25 '13 at 09:01
@Blender: it was a duplicate after all (OP changed `[1] [1] [1]` output to the expected `[1] [2] [3]`) – jfs Dec 25 '13 at 18:52

how could i distinguish default-parameter method in python

0 Answers0