This Bubble Sort lesson is for a beginner. Read the short notes, run each example, then change one name or number and run it again.
Bubble sort walks the list and swaps neighbours that are out of order. Large values drift to the end.
It is easy to see and slow on long lists. Use it to learn swaps, not to sort production data.
Example 1: Start here
The copy keeps the caller list unchanged.
def bubble(items): # define the function; it runs when you call it
items = items[:] # a separate copy
for i in range(len(items)): # repeat once per number; range stops before the last
for j in range(len(items) - 1 - i): # repeat once per number; range stops before the last
if items[j] > items[j + 1]: # run the indented lines only when this is true
items[j], items[j + 1] = items[j + 1], items[j] # swap the two values
return items # send this value back to the caller
print(bubble([4, 1, 3]))
Example 2: Walk the values
Bubble Sort starts by visiting one value at a time. Read the printed lines from top to bottom.
values = [13, 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 = [13, 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? Bubble Sort builds on that question.
values = [3, 13, 11] # a list; the values stay in this order
target = 13 # a whole number
print(target in values) # in is True when the value is found
The copy keeps the caller list unchanged.
