Introduction

We have already become acquainted with lists in the previous chapter. In this chapter of our online Python course we will present the dictionaries and the operators and methods on dictionaries. Python programs or scripts without lists and dictionaries are nearly inconceivable. Like lists dictionaries can easily be changed, can be shrunk and grown ad libitum at run time. They shrink and grow without the necessity of making copies. Dictionaries can be contained in lists and vice versa. But what’s the difference between lists and dictionaries? Lists are ordered sets of objects, whereas dictionaries are unordered sets. But the main difference is that items in dictionaries are accessed via keys and not via their position. A dictionary is an associative array (also known as hashes). Any key of the dictionary is associated (or mapped) to a value. The values of a dictionary can be any Python data type. So dictionaries are unordered key-value-pairs.

Dictionary don’t support the sequence operation of the sequence data types like strings, tuples and lists. Dictionaries belong to the built-in mapping type. They are the sole representative of this kind!

At the end of this chapter, we will show how a dictionary can be turned into one list, containing (key,value)-tuples or two lists, i.e. one with the keys and one with the values. This transformation can be done reversely as well. Continue reading Dictionaries →