Max Morlocke

Memory Leaks (in Python)

Mutable default arguments are usually a bug that can gobble memory.

For example,



In [1]:

    
def append_to(element, target=[]):
    target.append(element)
    return target



In [2]:

    
a = append_to('hello')
print(a)









    



['hello']



In [3]:

    
b = append_to('world')
print(b)









    



['hello', 'world']



In [4]:

    
a









    Out[4]:





['hello', 'world']



In [5]:

    
a is b









    Out[5]:





True

A better way of initializing to mutable data is shown below.



In [6]:

    
def append_to(element, target=None):
    if target is None:
        target = []
    target.append(element)
    return target



In [7]:

    
c = append_to('hello')
print(c)









    



['hello']



In [8]:

    
d = append_to('world')
print(d)









    



['world']



In [9]:

    
c









    Out[9]:





['hello']