Methods on Lists
Table of Contents
list.append(x)
Add an item x to the end of the list.
a = [1, 2, 3, 4, 5]
x = 100 # integer
a.append(x)
print(a) # [1, 2, 3, 4, 5, 100]
assert a[len(a) - 1 :] == [x]
b = ["s1", "s2"] # iterable
a.append(b)
print(a) # [1, 2, 3, 4, 5, 100, ['s1', 's2']
assert a[len(a) - 1 :] == [b]list.extend(iterable)
Extend the list by iterating over and appending all the items from the iterable
a = [1, 2, 3, 4, 5]
b = [100, 200, 300]
a.extend(b)
print(a) # [1, 2, 3, 4, 5, 100, 200, 300]list.insert(i, x)
At position i, insert item x
a = [1, 2, 3, 4, 5]
s = "a_string"
b = ["an", "iterable"]
a.insert(0, s) # insert at the beginning
print(a) # ['a_string', 1, 2, 3, 4, 5]
a.insert(len(a), b) # insert at the end
print(a) # ['a_string', 1, 2, 3, 4, 5, ['an', 'iterable']]
mid_element = len(a) // 2
a.insert(mid_element, "median") # insert at the middle
print(a) # ['a_string', 1, 2, 'median', 3, 4, 5, ['an', 'iterable']]list.remove(x)
Remove only the first instance of x (in place, nothing returned)
a = [1, 2, 3, 4, 5, "s", "z", "s"]
a.remove("s")
print(a) # [1, 2, 3, 4, 5, 'z', 's']list.pop([i])
Remove the item at the given position in the list, and return it. If no index is specified, a.pop() removes and returns the last item in the list.
a = [1, 2, 3, 4, 5]
a.pop() # 5
print(a) # [1, 2, 3, 4]
a.pop(0) # 1
print(a) # [2, 3, 4]
mid_element = len(a) // 2
a.pop(mid_element) # 3
print(a) # [2, 4]list.clear()
Remove all items from the list. Equivalent to del a[:]
a = [1, 2, 3, 4, 5]
a.clear()
print(a) # []list.count(x)
Return the number of times x appears in the list.
a = ["a", "b", "c"] * 3
print(a) # ['a', 'b', 'c', 'a', 'b', 'c', 'a', 'b', 'c']
x = "b"
a.count(x) # 3list.sort(*, key=None, reverse=False)
Sort the items of the list in place
a = [0, 3, 8, 2, 1, 10, 9]
a.sort()
print(a) # [0, 1, 2, 3, 8, 9, 10]
a.sort(reverse=True)
print(a) # [10, 9, 8, 3, 2, 1, 0]When sorting with a key, the order is determined by the return of the lambda function.
b = [3, 4, 0, -4, -3]
cubic = [(x, x ** 3) for x in b] # (x, f(x)=x^3)
print(cubic) # [(3, 27), (4, 64), (0, 0), (-4, -64), (-3, -27)]
b.sort(key=lambda x: x ** 3)
print(b) # [-4, -3, 0, 3, 4]
cubic.sort(key=lambda x: x[1])
print(cubic) # [(-4, -64), (-3, -27), (0, 0), (3, 27), (4, 64)]
assert b == [c[0] for c in cubic]list.reverse()
Reverse the elements of the list in place.
a = ["one", "to", "many"]
a.reverse()
print(a) # ['many', 'to', 'one']list.copy()
Return a shallow copy of the list. Equivalent to a[:]
a = ["a", "b", "c", "d"]
b = a.copy() # shallow copy
assert hex(id(a)) != hex(id(b))
assert b == a[:] and b is not a # same contents, different objects