Python WTF

gistfile1.txt

Python 2.7.7 (default, Jul 19 2014, 21:44:39)
[GCC 4.8.3] on linux2
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>>> [ 1, 2, 3 ] + "hi there"
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: can only concatenate list (not "str") to list
>>> x = [ 1,2,3 ];x += "hi there"; x
[1, 2, 3, 'h', 'i', ' ', 't', 'h', 'e', 'r', 'e']
>>>

Ya, the internal optimization of += to __iadd__ can have other fun implications… this one caused a bug in some of my code:

class Foo(object):
  def __init__(self):
    self._bar = []
  @property
  def bar(self):
    return self._bar

>>> x = Foo()
>>> x.bar += [1]
…
AttributeError: can't set attribute
>>> x.bar
[1]