Comprehensions

A comprehension builds a list from an existing sequence in one expression.

depths = [30, 12, 45, 7]

doubled = [depth * 2 for depth in depths]
print(doubled)

This is the same as building the list with a loop, and is the normal way to write it in Python.

Filtering

An if at the end keeps only the items that match.

depths = [30, 12, 45, 7]

passing = [depth for depth in depths if depth >= 30]
print(passing)

Transforming and filtering together

genes = ["tp53", "brca1", "egfr"]
print([gene.upper() for gene in genes if len(gene) == 4])

Dictionary and set comprehensions

The same syntax builds dictionaries and sets.

genes = ["TP53", "BRCA1"]
depths = [120, 88]

lookup = {gene: depth for gene, depth in zip(genes, depths)}
print(lookup)

sequence = "ATGGCCA"
print(sorted({base for base in sequence}))

When not to use one

A comprehension should fit on one or two lines and do one thing. If it needs several conditions, or a try, write a normal loop.

Task

Write passing_genes(records). It receives a list of (gene, depth) tuples and returns a list of gene names whose depth is 30 or more, uppercased, sorted alphabetically. Use a comprehension.