Syntax has some extra quirks to accommodate these. Lists are mutable, and their elements are usually homogeneous and areĪ special problem is the construction of tuples containing 0 or 1 items: the (or even by attribute in the case of namedtuples). Tuples are immutable, and usually contain an heterogeneous sequence ofĮlements that are accessed via unpacking (see later in this section) or indexing Though tuples may seem similar to lists, they are often used in different Items of a tuple, however it is possible to create tuples which contain mutable It is not possible to assign to the individual Parentheses, although often parentheses are necessary anyway (if the tuple is Tuples are interpreted correctly they may be input with or without surrounding v = (, ) > v (, )Īs you see, on output tuples are always enclosed in parentheses, so that nested t = 88888 Traceback (most recent call last):įile "", line 1, in TypeError: 'tuple' object does not support item assignment > # but they can contain mutable objects. List comprehensions can contain complex expressions and nested functions: > vec = > # create a new list with the values doubled > # filter the list to exclude negative numbers > # apply a function to all the elements > # call a method on each element > freshfruit = > # create a list of 2-tuples like (number, square) > # the tuple must be parenthesized, otherwise an error is raised > įile "", line 1 ^ Synta圎rror: invalid syntax > # flatten a list using a listcomp with two 'for' > vec =, , ] > Reverse the elements of the list, in place.Īn example that uses most of the list methods: Return the number of times x appears in the list. Return the index in the list of the first item whose value is x. Will see this notation frequently in the Python Library Reference.) list. Is optional, not that you should type square brackets at that position. Square brackets around the i in the method signature denote that the parameter Is specified, a.pop() removes and returns the last item in the list. Remove the item at the given position in the list, and return it. Remove the first item from the list whose value is x. ![]() ![]() The list, and a.insert(len(a), x) is equivalent to a.append(x). ![]() The first argument is the index of theĮlement before which to insert, so a.insert(0, x) inserts at the front of extend ( L )Įxtend the list by appending all the items in the given list equivalent to Here are all of the methods of listĪdd an item to the end of the list equivalent to a =. The list data type has some more methods.
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