do_not_ise_dict_as_kwarg_def

def i_am_wrong(d=dict()):
    key = "results"
    if key not in d:
        d[key] = list()
    d[key].append("Hi!")
    return d

print "No problems:"
print i_am_wrong(dict())
print i_am_wrong(dict())
print i_am_wrong(dict())

print "But what if we do not pass d?"
print i_am_wrong()
print i_am_wrong()
print i_am_wrong()

output

% python do_not_use_dict_as_arg.py
No problems:
{'results': ['Hi!']}
{'results': ['Hi!']}
{'results': ['Hi!']}
But what if we do not pass d?
{'results': ['Hi!']}
{'results': ['Hi!', 'Hi!']}
{'results': ['Hi!', 'Hi!', 'Hi!']}

Solution:

def i_am_ok(d=None):
    if d is None:
        d = dict()
    ...