Python Objects - or what's with the periods everywhere?

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Most things in Python are objects. But what is an object?

Every constant, variable, or function in Python is actually a object with a

type and associated attributes and methods. An *attribute* a property of

the object that you get or set by giving the <object_name> + dot +

<attribute_name>, for example ``img.shape``. A *method* is a function

that the object provides, for example ``img.argmax(axis=0)`` or ``img.min()``.

Use tab completion in IPython to inspect objects and start to understand

attributes and methods. To start off create a list of 4 numbers::

a = [3, 1, 2, 1]

a.<TAB>

This will show the available attributes and methods for the Python list

``a``. **Using <TAB>-completion and help is a very efficient way to learn and later

remember object methods!**

::

In [17]: a.<TAB>

a.__add__ a.__ge__ a.__iter__ a.__repr__ a.append

a.__class__ a.__getattribute__ a.__le__ a.__reversed__ a.count

a.__contains__ a.__getitem__ a.__len__ a.__rmul__ a.extend

a.__delattr__ a.__getslice__ a.__lt__ a.__setattr__ a.index

a.__delitem__ a.__gt__ a.__mul__ a.__setitem__ a.insert

a.__delslice__ a.__hash__ a.__ne__ a.__setslice__ a.pop

a.__doc__ a.__iadd__ a.__new__ a.__sizeof__ a.remove

a.__eq__ a.__imul__ a.__reduce__ a.__str__ a.reverse

a.__format__ a.__init__ a.__reduce_ex__ a.__subclasshook__ a.sort

For the most part you can ignore all the ones that begin with ``__`` since

they are generally are internal methods that are not called directly. At

the end you see useful looking functions like ``append`` or ``sort`` which

you can get help for and use::

a.sort

a.sort?

a.sort()

a

You can tell the difference between an attribute and a callable method with

the callable function::

callable(a.sort)

[x for x in dir(a) if callable(getattr(a, x)) and not x.startswith('__')]

*Mention classes and objects as class instances?*