def validate_jmespath_for_set(expression):
# Validates a limited jmespath expression to determine if we can set a value
# based on it. Only works with dotted paths.
if not expression or expression == '.':
raise InvalidExpressionError(expression=expression)
for invalid in ['[', ']', '*']:
if invalid in expression:
raise InvalidExpressionError(expression=expression)
def set_value_from_jmespath(source, expression, value, is_first=True):
# This takes a (limited) jmespath-like expression & can set a value based
# on it.
# Limitations:
# * Only handles dotted lookups
# * No offsets/wildcards/slices/etc.
if is_first:
validate_jmespath_for_set(expression)
bits = expression.split('.', 1)
current_key, remainder = bits[0], bits[1] if len(bits) > 1 else ''
if not current_key:
raise InvalidExpressionError(expression=expression)
if remainder:
if not current_key in source:
# We've got something in the expression that's not present in the
# source (new key). If there's any more bits, we'll set the key with
# an empty dictionary.
source[current_key] = {}
return set_value_from_jmespath(
source[current_key],
remainder,
value,
is_first=False
)
# If we're down to a single key, set it.
source[current_key] = value