Lists
Python has a number of built-in composite data structures: tuples, lists, sets, dictionaries. Here we take a look at lists and dictionaries.
A list stores many values in a single structure.
events = [267, 1332, 1772, 1994, 493, 1373, 1044, 156, 1515, 1788] # array of years
print('events:', events)
print('length:', len(events))
print('first item of events is', events[0]) # indexing starts witgh 0
events[2] = 1773 # individual elements are mutable
print('events is now:', events)
events.append(1239) # append at the end
events.append(606) # append at the end
print('events is now:', events)
events.pop(4) # remove element #4
print('events is now:', events)
events.remove(267) # remove by value (first occurrence)
a = [] # start with an empty list
a.append('Vancouver')
a.append('Toronto')
a.append('Kelowna')
print(a)
a[3] # will give an error message (past the end of the array)
a[-1] # display the last element; what's the other way?
a[:] # will display all elements
a[1:] # all elements starting from #1
a[:1] # ending with but not including #1
Lists can be heterogeneous and nested:
a = [11, 21., 3.5]
b = ['Mercury', 'Venus', 'Earth']
c = 'hello'
nestedList = [a, b, c]
print(nestedList)
Question 5.1: double subsetting
How would you extract element “Earth” fromnestedList?
You can search inside a list:
'Venus' in b # returns True
'Pluto' in b # returns False
b.index('Venus') # returns 1 (positional index)
nestedList[1].index('Venus') # same
And you sort lists alphabetically:
b.sort()
b # returns ['Earth', 'Mercury', 'Venus']