name : _transformations.py import re try: from inspect import Parameter, signature except ImportError: signature = None from inspect import getfullargspec _EMPTY_SENTINEL = object() def inc(x): """ Add one to the current value """ return x + 1 def dec(x): """ Subtract one from the current value """ return x - 1 def discard(evolver, key): """ Discard the element and returns a structure without the discarded elements """ try: del evolver[key] except KeyError: pass # Matchers def rex(expr): """ Regular expression matcher to use together with transform functions """ r = re.compile(expr) return lambda key: isinstance(key, str) and r.match(key) def ny(_): """ Matcher that matches any value """ return True # Support functions def _chunks(l, n): for i in range(0, len(l), n): yield l[i:i + n] def transform(structure, transformations): r = structure for path, command in _chunks(transformations, 2): r = _do_to_path(r, path, command) return r def _do_to_path(structure, path, command): if not path: return command(structure) if callable(command) else command kvs = _get_keys_and_values(structure, path[0]) return _update_structure(structure, kvs, path[1:], command) def _items(structure): try: return structure.items() except AttributeError: # Support wider range of structures by adding a transform_items() or similar? return list(enumerate(structure)) def _get(structure, key, default): try: if hasattr(structure, '__getitem__'): return structure[key] return getattr(structure, key) except (IndexError, KeyError): return default def _get_keys_and_values(structure, key_spec): if callable(key_spec): # Support predicates as callable objects in the path arity = _get_arity(key_spec) if arity == 1: # Unary predicates are called with the "key" of the path # - eg a key in a mapping, an index in a sequence. return [(k, v) for k, v in _items(structure) if key_spec(k)] elif arity == 2: # Binary predicates are called with the key and the corresponding # value. return [(k, v) for k, v in _items(structure) if key_spec(k, v)] else: # Other arities are an error. raise ValueError( "callable in transform path must take 1 or 2 arguments" ) # Non-callables are used as-is as a key. return [(key_spec, _get(structure, key_spec, _EMPTY_SENTINEL))] if signature is None: def _get_arity(f): argspec = getfullargspec(f) return len(argspec.args) - len(argspec.defaults or ()) else: def _get_arity(f): return sum( 1 for p in signature(f).parameters.values() if p.default is Parameter.empty and p.kind in (Parameter.POSITIONAL_ONLY, Parameter.POSITIONAL_OR_KEYWORD) ) def _update_structure(structure, kvs, path, command): from pyrsistent._pmap import pmap e = structure.evolver() if not path and command is discard: # Do this in reverse to avoid index problems with vectors. See #92. for k, v in reversed(kvs): discard(e, k) else: for k, v in kvs: is_empty = False if v is _EMPTY_SENTINEL: if command is discard: # If nothing there when discarding just move on, do not introduce new nodes continue # Allow expansion of structure but make sure to cover the case # when an empty pmap is added as leaf node. See #154. is_empty = True v = pmap() result = _do_to_path(v, path, command) if result is not v or is_empty: e[k] = result return e.persistent()