Viewing file:  _transformations.py (3.5 KB) -rw-r--r--
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import re
import six
try:
from inspect import Parameter, signature
except ImportError:
signature = None
try:
from inspect import getfullargspec as getargspec
except ImportError:
from inspect import getargspec
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, six.string_types) 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):
from pyrsistent._pmap import pmap
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, pmap()))]
if signature is None:
def _get_arity(f):
argspec = getargspec(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):
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:
result = _do_to_path(v, path, command)
if result is not v:
e[k] = result
return e.persistent()
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