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Structured data in environment variables: nested dictionaries and lists
def normalise_environment(key_values):
''' Converts denormalised dict of (string -> string) pairs, where the first string
is treated as a path into a nested list/dictionary structure
"FOO__1__BAR": "setting-1",
"FOO__1__BAZ": "setting-2",
"FOO__2__FOO": "setting-3",
"FOO__2__BAR": "setting-4",
"FIZZ": "setting-5",
to the nested structure that this represents
"FOO": [{
"BAR": "setting-1",
"BAZ": "setting-2",
}, {
"FOO": "setting-3",
"BAR": "setting-4",
"FIZZ": "setting-5",
If all the keys for that level parse as integers, then it's treated as a list
with the actual keys only used for sorting
This function is recursive, but it would be extremely difficult to hit a stack
limit, and this function would typically by called once at the start of a
program, so efficiency isn't too much of a concern.
Copyright (c) 2018 Department for International Trade. All rights reserved.
This work is licensed under the terms of the MIT license.
For a copy, see
# Separator is chosen to
# - show the structure of variables fairly easily;
# - avoid problems, since underscores are usual in environment variables
separator = '__'
def get_first_component(key):
return key.split(separator)[0]
def get_later_components(key):
return separator.join(key.split(separator)[1:])
without_more_components = {
key: value
for key, value in key_values.items()
if not get_later_components(key)
with_more_components = {
key: value
for key, value in key_values.items()
if get_later_components(key)
def grouped_by_first_component(items):
def by_first_component(item):
return get_first_component(item[0])
# groupby requires the items to be sorted by the grouping key
return itertools.groupby(
sorted(items, key=by_first_component),
def items_with_first_component(items, first_component):
return {
get_later_components(key): value
for key, value in items
if get_first_component(key) == first_component
nested_structured_dict = {
**without_more_components, **{
first_component: normalise_environment(
items_with_first_component(items, first_component))
for first_component, items in grouped_by_first_component(with_more_components.items())
def all_keys_are_ints():
def is_int(string):
return True
except ValueError:
return False
return all([is_int(key) for key, value in nested_structured_dict.items()])
def list_sorted_by_int_key():
return [
for key, value in sorted(
key=lambda key_value: int(key_value[0])
return \
list_sorted_by_int_key() if all_keys_are_ints() else \
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