Functional Programming

notes from the field.

In general,

new_collection = collection.map(function)

is a short-cut for:

new_collection[]
for (element in collection)
 new_collection[] += function(element)

And:

new_collection = collection.filter(function)

is a short-cut for:

new_collection[]
for (element in collection):
  if function(element):
    new_collection[] += function(element)

this

doubled = [1, 2, 3, 4, 5].map(x => x * 2)

is equivalent to:

doubled[]
for (x in [1, 2, 3, 4, 5]):
  doubled[] += x * 2

that

Example

you want to remove all the gcp images not in use, get all the current live instance, find their template, find the image in the template and "subtract" those from the list of all images.

source_images = instance
  .map(i => i.get_template)
  .map(i => i.get_source_image)

to_delete = gci.get_all()
  .filter(i => !source_images[i])
  .filter(i => i.age > 1m)

for i in to_delete:
  i.delete()