List Methods
Lists are objects and thus have methods. Table 11, List Methods gives some of the most commonly used list methods.
|
Method |
Description |
|---|---|
|
L.append(v) |
Appends value v to list L. |
|
L.clear() |
Removes all items from list L. |
|
L.count(v) |
Returns the number of occurrences of v in list L. |
|
L.extend(v) |
Appends the items in v to L. |
|
L.index(v) |
Returns the index of the first occurrence of v in L—an error is raised if v doesn’t occur in L. |
|
L.index(v, beg) |
Returns the index of the first occurrence of v at or after index beg in L—an error is raised if v doesn’t occur in that part of L. |
|
L.index(v, beg, end) |
Returns the index of the first occurrence of v between indices beg (inclusive) and end (exclusive) in L; an error is raised if v doesn’t occur in that part of L. |
|
L.insert(i, v) |
Inserts value v at index i in list L, shifting subsequent items to make room. |
|
L.pop() |
Removes and returns the last item of L (which must be nonempty). |
|
L.remove(v) |
Removes the first occurrence of value v from list L. |
|
L.reverse() |
Reverses the order of the values in list L. |
|
L.sort() |
Sorts the values in list L in ascending order (for strings with the same letter case, it sorts in alphabetical order). |
|
L.sort(reverse=True) |
Sorts the values in list L in descending order (for strings with the same letter case, it sorts in reverse alphabetical order). |
Here is a sample interaction showing how we can use list methods to construct a list of many colors:
| | >>> colors = ['red', 'orange', 'green'] |
| | >>> colors.extend(['black', 'blue']) |
| | >>> colors |
| | ['red', 'orange', 'green', 'black', 'blue'] |
| | >>> colors.append('purple') |
| | >>> colors |
| | ['red', 'orange', 'green', 'black', 'blue', 'purple'] |
| | >>> colors.insert(2, 'yellow') |
| | >>> colors |
| | ['red', 'orange', 'yellow', 'green', 'black', 'blue', 'purple'] |
| | >>> colors.remove('black') |
| | >>> colors |
| | ['red', 'orange', 'yellow', 'green', 'blue', 'purple'] |
All the methods shown here modify the list instead of creating a new list. The same is true for the methods clear, reverse, sort, and pop. Of those methods, only pop returns a value other than None. (pop returns the item that was removed from the list.) In fact, the only method that returns a list is copy, which is equivalent to L[:].
Finally, a call to append isn’t the same as using +. First, append appends a single value, while + expects two lists as operands. Second, append modifies the list rather than creating a new one.