Methods that start and end with ___
<p>I have noticed that in Python some of the fundamental types have two types of methods: those that are surrounded by <code>__</code> and those that don't. </p>

<p>For example, if I have a variable of type <code>float</code> called <code>my_number</code>, I can see in IPython that it has the following methods:</p>

<pre><code>my_number.__abs__           my_number.__pos__
my_number.__add__           my_number.__pow__
my_number.__class__         my_number.__radd__
my_number.__coerce__        my_number.__rdiv__
my_number.__delattr__       my_number.__rdivmod__
my_number.__div__           my_number.__reduce__
my_number.__divmod__        my_number.__reduce_ex__
my_number.__doc__           my_number.__repr__
my_number.__eq__            my_number.__rfloordiv__
my_number.__float__         my_number.__rmod__
my_number.__floordiv__      my_number.__rmul__
my_number.__format__        my_number.__rpow__
my_number.__ge__            my_number.__rsub__
my_number.__getattribute__  my_number.__rtruediv__
my_number.__getformat__     my_number.__setattr__
my_number.__getnewargs__    my_number.__setformat__
my_number.__gt__            my_number.__sizeof__
my_number.__hash__          my_number.__str__
my_number.__init__          my_number.__sub__
my_number.__int__           my_number.__subclasshook__
my_number.__le__            my_number.__truediv__
my_number.__long__          my_number.__trunc__
my_number.__lt__            my_number.as_integer_ratio
my_number.__mod__           my_number.conjugate
my_number.__mul__           my_number.fromhex
my_number.__ne__            my_number.hex
my_number.__neg__           my_number.imag
my_number.__new__           my_number.is_integer
my_number.__nonzero__       my_number.real
</code></pre>

<ol>
<li>What is the difference between those that are surrounded by <code>___</code>  and those that aren't? </li>
<li>Is this some sort of  <strong>standard</strong> used in other programming languages? Does it usually mean the same thing in similar languages?</li>
</ol>
