Built-in class list

• Unlike ranges, lists are mutable — their elements can be modified, new elements can be added, and existing elements can be removed, they can also be sliced and subscripted.

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Literals, operators, functions, and methods

• The empty list literal is []

• If s is a list then len(s) is the number of elements in s.

• If s is a list then del s[a:b] removes the elements from s with indices a through b-1.

• The + operator can combine two lists to produce a new list. If s and t are lists, then u = s + t makes u a new list. The number of elements in u is len(s) + len(t). List u corresponds to the list of values in s concatenated with the list of values in t.

• The append() method adds a new element to the end of a list. If s is a list, then s.append(x) grows the size of s by one by appending an element x to the end of list s.

• Method clear() can clear out the elements of a list. If s is a list, then s.clear() removes all elements from s.

• Method copy() produces a copy of its list. If s is a list, then s.copy() returns a new list, which has the same values as s.

• Method count() counts occurrences in a list. If s is a list, then s.count(x) returns the number of elements in s equal to x.

• The in and not in operators determine whether values are or are not part of a list. If s is a list, then x in s is True when x is one of the elements of s, and x not in s is true when x is not one of the elements of s.

• The index() method has several forms for inspecting a list. Suppose s is a list, x is a value, and n is the length of s (i.e., n = len(s).

• s.index(x) determines the index of the first occurrence of x in list s.

• s.index(x, i) determines the index of the first occurrence of x in list s among the elements with indices i ... n-1.

• s.index(x, i, j) determines the index of the first occurrence of x in list s among the elements with indices i ... j-1.

Note, if index() cannot find x in s then an error occurs.

• The insert() method inserts a new element into a list. If s is a list, then s.insert(a, x) grows the size of s by one by inserting a new element x into s at index a.

• The pop() method removes an element from a list and retrieve its value. There are two forms of the pop() method. Suppose s is a list.

• s.pop() returns the last element in s and also removes it from the list s.

• s.pop(i) returns the element with index i from its list s and also removes it from the list s.

Method pop() differs from the related method remove() in that pop()'s argument is an index to remove a value from while remove()'s is a value to remove from the list s.

• The remove() method can be used to remove a value from a list. If s is a list, then s.remove(x) removes the first occurrence of x from s.

Method remove() differs from the related method pop() in that remove()'s argument is a value to be removed while pop()'s is an index to remove a value from.

• The reverse() method can be used to reverse values in a list. If s is a list, then s.reverse() reverses the order of element values in s.

• Method sort() puts its list into sorted order. If s is a list, then s.sort() rearranges the elements of s into non-descending order.

• The built-in function max() returns the "largest" value in a list. If s is a list, max(s) is an element of s that has the largest value. Function max() requires the elements of the list to be comparable (usually meaning they all have the same type).

• The built-in function min() returns the "smallest" value in a list. If s is a list, min(s) is an element of s that has the smallest value. Function min() requires the elements of the list to be comparable (usually meaning they all have the same type).

• The built-in function sorted() returns a new list whose elements are in sorted order. If s is a list, then sorted(s) returns a new list whose elements are those of s but in sorted order. Function sorted() requires the elements of the list to be comparable (usually meaning they all have the same type).

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Common usage patterns

To accumulate something across all elements of a list. Suppose s is a list.

# initialize result to 0, 1, [] or '' depending on what is being built

result = ...

# process elements of s one by one

for element in s:

    # examine element to determine its part in the accumulation.

    ...

    # add the computed part to the accumulation.

    ...

Build a new list by converting the elements of an existing list to values of a different type. Suppose s is a list.

# t is to be new list, it has has no elements as of yet

t = []

# process elements of s one by one

for element in s :

    # examine element to determine its conversion value; e.g.,

    # string to number

    value = ...

    # add the value to the accumulation list

    t.append( value )

 

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