Lists

A list is an ordered, changeable sequence of values. Lists hold anything, and are the default container for a collection of records.

genes = ["TP53", "BRCA1", "EGFR"]

print(genes[0])
print(genes[-1])
print(len(genes))

Changing a list

genes = ["TP53", "BRCA1"]

genes.append("EGFR")
genes.insert(0, "KRAS")
genes.remove("BRCA1")
print(genes)

popped = genes.pop()
print(popped, genes)

Sorting

sort() changes the list in place and returns None. sorted() returns a new list and leaves the original alone.

depths = [30, 12, 45, 7]

print(sorted(depths))
print(sorted(depths, reverse=True))
print(depths)

depths.sort()
print(depths)

Sort by something other than the value itself with key:

genes = ["TP53", "BRCA1", "EGFR"]
print(sorted(genes, key=len))

Slicing returns a copy

depths = [30, 12, 45, 7]
first_two = depths[:2]
first_two[0] = 999
print(depths[0])

Assigning a list to a second name does not copy it. Both names refer to the same list.

a = [1, 2, 3]
b = a
b.append(4)
print(a)

Use a.copy() or a[:] when you need an independent list.

Task

Write top_n(values, n). It receives a list of integers and returns the n largest, in descending order, as a list. Do not modify the input list.