Lists
Store an ordered collection of items and change it as you go.
A list holds several values in order, inside square brackets. Lists can grow, shrink and change, which makes them Python's most used collection.
Python
marks = [78, 92, 65]
print(marks)
print(marks[0], marks[-1])
print(len(marks))Output
[78, 92, 65] 78 65 3
Changing a list
Python
tasks = ["read", "code"]
tasks.append("sleep") # add to the end
tasks.insert(0, "wake up") # add at a position
tasks[2] = "write code" # replace an item
print(tasks)
tasks.remove("read") # remove by value
last = tasks.pop() # remove and return the last item
print(tasks, last)Output
['wake up', 'read', 'write code', 'sleep'] ['wake up', 'write code'] sleep
Sorting and searching
Python
nums = [42, 7, 19, 7, 88]
print(sorted(nums)) # new sorted list
print(max(nums), min(nums), sum(nums))
print(nums.count(7), nums.index(19))
nums.sort(reverse=True) # sorts the list itself
print(nums)Output
[7, 7, 19, 42, 88] 88 7 163 2 2 [88, 42, 19, 7, 7]
List comprehensions
A list comprehension builds a new list from an existing one in a single line. Read it as "give me this expression, for each item, if a condition holds".
Python
numbers = range(1, 11)
squares = [n * n for n in numbers]
evens = [n for n in numbers if n % 2 == 0]
print(squares)
print(evens)Output
[1, 4, 9, 16, 25, 36, 49, 64, 81, 100] [2, 4, 6, 8, 10]