Questions #1

for key in { 'foo' : 1 , 'bar' : 2 }:
process_key(key)

How to iterate a dictionary over key-value pairs?
The .iteritems() dictionary method returns a (key, value) tuple generator.

Classes, objects

How to get a list of object attributes?
The dir function returns a list of strings - fields of the object. The __dict__ field contains a dictionary of the form {field -> value}.
What are magical methods, what are they for?
Magic methods are methods whose names begin and end with a double underscore. They are magical because they are almost never called explicitly. They are called by built-in functions or syntactic constructs. For example, the len() function calls the __len__() method of the passed object. The __add__(self, other) method is called automatically when added with the + operator.
Here are some magical methods:

• 
  __init__: class constructor
  
• 
  __add__: addition with another object
  
• 
  __eq__: test for equality with another object
  
• 
  __cmp__: comparison (greater than, less than, equal to)
  
• 
  __iter__: when substituting an object in a loop
  

How can I refer to the parent class in a class?
The super function takes a class and an instance:
class NextClass (FirstClass):
def __init__ ( self , x):
super (NextClass, self ).__init__()
self .x = x

Is multiple inheritance possible? What is MRO?
Yes, you can specify more than one parent in a child class.
MRO - method resolution order, method resolution order. The algorithm by which the method should be searched if the class has two or more parents. The algorithm linearizes the inheritance graph. Briefly, it can be described as follows: search from left to right. Therefore, the more to the right a class is, the less priority it has when searching for a method.