More About Lists#

List Access#

In addition to sequence access …

  • L.append(elem): append elem to the list

  • L.extend(l): extend L with another sequence l

  • L.insert(i, elem): insert elem at position i (same as L[i:i] = elem)

  • L.pop(i): remove element at i from the list (and return its value)

  • L.sort(): sort the list in place. Elements must be comparable ⟶ careful with mixed lists!

  • L.reverse(): reverses the list in place

  • sorted(L): return a sorted copy of the list

  • reversed(L): returns a reversed copy of the list

List Methods: Examples#

>>> l = [3, 2, 5]
>>> l.append(3)
>>> l
[3, 2, 5, 3]
>>> l.extend([3, 2])
>>> l.sort()
>>> l
[2, 2, 3, 3, 3, 5]
>>> l.reverse()
>>> l
[5, 3, 3, 3, 2, 2]
>>> sorted(l)
[2, 2, 3, 3, 3, 5]

List Comprehension#

The best way to write good code is to write as little code as possible …

Best explained by example#
>>> [i**2 for i in [1, 2, 3]]
[1, 4, 9]
Traditional alternative#
def square_numbers(numbers):
    ret = []
    for i in numbers:
        ret.append(i**2)
    return ret
sqn = square_numbers([1,2,3])