This Copy Lists lesson is for a beginner. Read the short notes, run each example, then change one name or number and run it again.
Assigning a list to a second name shares one list. copy builds a new list with the same items.
A slice of the whole list, skills[:], is another way to copy. Both are shallow: a list stored inside is still shared.
Example 1: Start here
fresh stays [Python, SQL]. skills and alias both gain Git.
skills = ["Python", "SQL"] # a list; the values stay in this order
alias = skills # another name for the same value
fresh = skills.copy() # a separate copy
alias.append("Git") # add one item at the end of the list
print(skills)
print(fresh)
Example 2: Copy before you change
copy gives you a separate list. Appending to one does not change the other.
scores = [70, 80] # a list; the values stay in this order
backup = scores.copy() # a separate copy
scores.append(90) # add one item at the end of the list
print(backup)
print(scores)
Example 3: A slice copy
scores[:] is another way to copy the whole list.
scores = [70, 80, 90] # a list; the values stay in this order
backup = scores[:] # a separate copy
print(backup)
Example 4: Two names, one list
Assignment does not copy. Both names see the appended 90.
scores = [70, 80] # a list; the values stay in this order
alias = scores # another name for the same value
alias.append(90) # add one item at the end of the list
print(scores)
fresh stays [Python, SQL]. skills and alias both gain Git.
