def apply_replacements(conf: Property) -> Property:
"""Apply a set of replacement values to a config file, returning a new copy.
The replacements are found in a 'Replacements' block in the property.
These replace %values% starting and ending with percents. A double-percent
allows literal percents. Unassigned values are an error.
"""
replace = {}
new_conf = Property(conf.real_name, [])
# Strip the replacement blocks from the config, and save the values.
for prop in conf:
if prop.name == 'replacements':
for rep_prop in prop:
replace[rep_prop.name.strip('%')] = rep_prop.value
else:
new_conf.append(prop)
def rep_func(match: Match):
"""Does the replacement."""
var = match.group(1)
if not var: # %% becomes %.
return '%'
try:
return replace[var.casefold()]
except KeyError:
raise ValueError('Unresolved variable: {!r}\n{}'.format(
var, replace))
for prop in new_conf.iter_tree(blocks=True):
prop.name = RE_PERCENT_VAR.sub(rep_func, prop.real_name)
if not prop.has_children():
prop.value = RE_PERCENT_VAR.sub(rep_func, prop.value)
return new_conf
