This Lists and Arrays lesson is for a beginner. Read the short notes, run each example, then change one name or number and run it again.
A Python list is the array you will use most. Indexing is fast. Inserting at the front moves every later item.
Store items that you read by position in a list. Store items that you read by name in a dict.
Example 1: Start here
append is cheap. insert(0, value) is not, once the list is long.
items = ["Python", "SQL", "Git"] # a list; the values stay in this order
print(items[1])
items.append("Excel") # add one item at the end of the list
print(items)
Example 2: Walk the values
Lists and Arrays starts by visiting one value at a time. Read the printed lines from top to bottom.
values = [21, 3, 11, 7] # a list; the values stay in this order
for value in values: # repeat the indented lines once per value
print(value)
Example 3: Keep the largest
Many data-structure lessons reduce a list to one answer. This one remembers the largest number seen so far.
values = [21, 3, 11, 7] # a list; the values stay in this order
best = values[0] # the first value
for value in values: # repeat the indented lines once per value
if value > best: # run the indented lines only when this is true
best = value # another name for the same value
print(best)
Example 4: Search for a target
A search asks one yes-or-no question: is the target in the collection? Lists and Arrays builds on that question.
values = [3, 21, 11] # a list; the values stay in this order
target = 21 # a whole number
print(target in values) # in is True when the value is found
append is cheap. insert(0, value) is not, once the list is long.
