def default argument value

  
 プログラムソース
  
# important

def f(a,L=[]):
    L.append(a)
    return L

print('f  output')
print(f(1))
print(f(2))
print(f(3))

def f2(a,L=None):
    if L==None:
        L=[]
    L.append(a)
    return L

print('f2  output')
print(f2(1))
print(f2(2))
print(f2(3))
  
  
===== RESTART: C:/python/Def_importantWarning.py ===
f  output
[1]
[1, 2]
[1, 2, 3]
f2  output
[1]
[2]
[3]
>>>