> min(timeit.repeat(lambda: append(, "abcdefghijklmnopqrstuvwxyz"))) The following functions do the same thing: def append(alist, iterable): You may wonder what is more performant, since append can be used to achieve the same outcome as extend. Total time for all appends is linear at O(n), and that time allocated per append, becomes O(1). This means that we get the benefits of a larger than needed memory reallocation up front, but we may pay for it on the next marginal reallocation with an even larger one. * sequence of appends() in the presence of a poorly-performing * enough to give linear-time amortized behavior over a long Regarding "amortized" - from the list object implementation source: /* This over-allocates proportional to the list size, making room append() adds to the complexity, making it equivalent to that of extend, and since extend's iteration is implemented in C, it will always be faster if you intend to append successive items from an iterable onto a list. ![]() Time ComplexityĪppend has ( amortized) constant time complexity, O(1). It also works like extend, in that the second iterable can be any kind of iterable.ĭon't get confused - my_list = my_list + another_list is not equivalent to += - it gives you a brand new list assigned to my_list. My_list += another_list modifies the list in-place (it is the in-place operator, and lists are mutable objects, as we've seen) so it does not create a new list. My_list + another_list creates a third list in memory, so you can return the result of it, but it requires that the second iterable be a list. Operator Overload, _add_ ( +) and _iadd_ ( +=)īoth + and += operators are defined for list. Keep in mind that a string is an iterable, so if you extend a list with a string, you'll append each character as you iterate over the string (which may not be what you want): > my_list.extend('baz') So with extend, each element of the iterable gets appended onto the list. extend() method extends a list by appending elements from an iterable: my_list.extend(iterable) #^^^^^^^^^- single item at the end of the list. If you append another list onto a list, the first list will be a single object at the end of the list (which may not be what you want): > another_list = So keep in mind that a list is an object. Whatever the object is, whether a number, a string, another list, or something else, it gets added onto the end of my_list as a single entry on the list. ![]() append() method appends an object to the end of the list. The length of the list will increase by however many elements were in the iterable argument. extend() iterates over its argument adding each element to the list, extending the list. The length of the list itself will increase by one. append() adds its argument as a single element to the end of a list. What is the difference between the list methods append and extend?
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