Wednesday, October 24, 2012

Map in python - and it's application to ini file reader

Mapping Types is a container that maps from an element to the other element. In python, map is implement in dict.

Making a map(dirctionary) in python

Dictionary is represented as follows:
e = {"one": 1, "two": 2}
The two items are mapped with ":" charactore, and each mapping is separated by a comman. Python builds dict object with '{' and '}' character.

You can use dict() method to build one.
class dict(**kwarg)
You may not familiar with ** notation. This is a simple example used in python method.
def hello(**x):
    print x

When you execute this code, you will get a dictionary object.
{'y': 2, 'x': 1}
When python method sees **something, all the assignments (x = 1, y = 2 in this example) given as a parameter is wrapped inside an automatically generated dictionary, and parameter variable x is pointing to the dictionary. In short, you can think of **something as collect (*) and make dictionary (*), and name it something.

As you see the meaning of **something as a parameter to the function. You'll see that this code will make the same dictionary as before.
a = dict(one=1, two=2)
You have more options to make the dictionary.
class dict(mapping, **kwarg)
class dict(iterable, **kwarg)
For the first case, when first item is a mapping (other dictionary), it will build a new dictionary with the contents of it together with the additional parameters.
b = dict({'one': 1, 'two': 2})
For the next case, the first parameter can be a list with lists that has two elements.
c = dict(zip(('one', 'two'), (1, 2)))
d = dict([['two', 2], ['one', 1]])
zip method has two parameters, and iterate over the elements in each of the two elements to zip a list of list that contains two elements from each parameters.

Of course, you can add additional assignments so that they are added to the newly generated dictionary.

Using dictionary

For getting all the items in a dictionary, you need to use items().
d = {'banana': 3, 'apple':4, 'pear': 1, 'orange': 2}
print d
print d.items()
{'orange': 2, 'pear': 1, 'banana': 3, 'apple': 4}
[('orange', 2), ('pear', 1), ('banana', 3), ('apple', 4)]

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