problem with special built-in method __contains__,

[eboy98 at gmail.com]

if i have a dictionary  name number ....and i want to    ask the list
whether a particular key already
exists.

>>> print number
{'octal': '1234567', 'binary': '10100101', 'decimal': '1234567890',
'hexadecimal': '1-9,a-f'}

 i got  error..after execute

 >>>number._contains_("test")

Traceback (most recent call last):
  File "<pyshell#15>", line 1, in <module>
    number._contains_("test")
AttributeError: 'dict' object has no attribute '_contains_'