A Comprehensive Introduction to Python Programming and ... - MSDL

1.2 Language Features 9 / 75
>> list = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>> list[1:7]
[1, 2, 3, 4, 5, 6]
>>
It is possible to assign a list to a slice to modify part of an existing list, as shown
below. Assigning an empty list to a slice deleted the slice from the original list.
Listing 4: Slice Assignment
>> list = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>> list[1:6] = [’a’, ’b’]
[0, ’a’, ’b’, 6, 7, 8, 9, 10]
>>
The colon operator has some interesting defaults. When its left-hand side is not
specified, it defaults to 0. When its right-hand side is not specified, it defaults to the
length of the list. Therefore, the Python instruction list name[:] will return the
entire list.
The built-in function len( ) can be used to obtain the length of a list. It is also
possible to concatenate lists by using the ’+’ operator.
1.2.4.2 Tuples
Tuples simply consist of a series of values enclosed within parentheses. Here is an
example of a tuple:
(’arial’, 10, ’bold’)
Tuples work exactly like lists, except for the fact that they are immutable, which
means that their elements cannot be modified in place. However, the values stored in
the components of a tuple can be modified. In other words, a tuple should be thought
of as holding references (or pointers) to other objects. Consider the following two
examples. The first one shows that trying to change the elements of a tuple is not
allowed. The second one shows that it is possible to modify a mutable element which
is inside of a tuple. Note the fundamental difference between the two examples.
Listing 5: Tuple Example 1
>> list = [’a’, ’f’, ’c’]
>> tuple = (10, list, ’string constant’)
>> tuple[1]
[’a’, ’f’, ’c’]
>> tuple[1] = [’some’, ’other’, ’list’] 5