TYPES 25 For user-defined classes, str and repr can be defined/redefined using the special operators str and repr . These are briefly described later on; for more, refer to the official Python documentation [38]. repr always has a default value. Another important characteristic of a Python string is that, like a list, it is an iterable object. 1 2 3 4 5 6 7 for i in 'hello': print i h e l l o list The main methods of a Python list are append, insert, and delete: 1 2 3 4 5 6 7 8 9 10 a = [1, 2, 3] print type(a). | TYPES 25 1 2 3 4 5 6 7 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 1 2 3 4 1 2 3 4 5 6 For user-defined classes str and repr can be defined redefined using the special operators str and __repr These are briefly described later on for more refer to the official Python documentation 38 . repr always has a default value. Another important characteristic of a Python string is that like a list it is an iterable object. for i in hello print i h e l l o list The main methods of a Python list are append insert and delete a 1 2 3 print type a type list 8 2 7 del a 0 print a 2 7 3 8 print len a 4 Lists can be sliced print a 3 2 7 3 print a 1 7 3 8 print a -2 3 8 and concatenated a 2 3 b 5 6 print a b 2 3 5 6 A list is iterable you can loop over it a 1 2 3 for i in a print i 1 2 3 26 THE PYTHON LANGUAGE The elements of a list do not have to be of the same type they can be any type of Python object. tuple A tuple is like a list but its size and elements are immutable while in a list they are mutable. If a tuple element is an object the object attributes are mutable. A tuple is delimited by round brackets. 1 a 1 2 3 So while this works for a list 1 a 1 2 3 2 a 1 5 3 print a 4 1 5 3 the element assignment does not work for a tuple 1 a 1 2 3 2 print a 1 32 4 a 1 5 5 Traceback most recent call last 6 File stdin line 1 in module 7 TypeError tuple object does not support item assignment The tuple like the list is an iterable object. Notice that a tuple consisting of a single element must include a trailing comma as shown below 1 a 1 2 print type a 3 type int 4 a 1 5 print type a 6 type tuple Tuples are very useful for efficient packing of objects because of their immutability and the brackets are often optional 1 a 2 3 hello 2 x y z a 3 print x 42 5 print z 6 hello diet A Python dictionary is a hash table that maps a key object to a value object. For example TYPES 27 1 2 3 4 5 6 7 8 9 1 2 3 4 5 1 2 3 4 5 6 7 1 2 3 4 5 6 7 8 1 2 a k v k2 3 a k v a k2 3 k True .
