Source code for glom.core

"""*glom gets results.*

If there was ever a Python example of "big things come in small
packages", ``glom`` might be it.

The ``glom`` package has one central entrypoint,
:func:`glom.glom`. Everything else in the package revolves around that
one function.

A couple of conventional terms you'll see repeated many times below:

* **target** - glom is built to work on any data, so we simply
  refer to the object being accessed as the *"target"*
* **spec** - *(aka "glomspec", short for specification)* The
  accompanying template used to specify the structure of the return

Now that you know the terms, let's take a look around glom's powerful


from __future__ import print_function

import sys
import pdb
import weakref
import operator
from abc import ABCMeta
from pprint import pprint
from collections import OrderedDict

from boltons.typeutils import make_sentinel
from boltons.iterutils import is_iterable

PY2 = (sys.version_info[0] == 2)
if PY2:
    _AbstractIterableBase = object
    from .chainmap_backport import ChainMap
    basestring = str
    _AbstractIterableBase = ABCMeta('_AbstractIterableBase', (object,), {})
    from collections import ChainMap

_type_type = type

_MISSING = make_sentinel('_MISSING')
SKIP =  make_sentinel('SKIP')
SKIP.__doc__ = """
The ``SKIP`` singleton can be returned from a function or included
via a :class:`~glom.Literal` to cancel assignment into the output

>>> target = {'a': 'b'}
>>> spec = {'a': lambda t: t['a'] if t['a'] == 'a' else SKIP}
>>> glom(target, spec)
>>> target = {'a': 'a'}
>>> glom(target, spec)
{'a': 'a'}

Mostly used to drop keys from dicts (as above) or filter objects from

.. note::

   SKIP was known as OMIT in versions 18.3.1 and prior. Versions 19+
   will remove the OMIT alias entirely.
OMIT = SKIP  # backwards compat, remove in 19+

STOP = make_sentinel('STOP')
STOP.__doc__ = """
The ``STOP`` singleton can be used to halt iteration of a list or
execution of a tuple of subspecs.

>>> target = range(10)
>>> spec = [lambda x: x if x < 5 else STOP]
>>> glom(target, spec)
[0, 1, 2, 3, 4]

[docs]class GlomError(Exception): """The base exception for all the errors that might be raised from :func:`glom` processing logic. By default, exceptions raised from within functions passed to glom (e.g., ``len``, ``sum``, any ``lambda``) will not be wrapped in a GlomError. """ pass
[docs]class PathAccessError(AttributeError, KeyError, IndexError, GlomError): """This :exc:`GlomError` subtype represents a failure to access an attribute as dictated by the spec. The most commonly-seen error when using glom, it maintains a copy of the original exception and produces a readable error message for easy debugging. If you see this error, you may want to: * Check the target data is accurate using :class:`~glom.Inspect` * Catch the exception and return a semantically meaningful error message * Use :class:`glom.Coalesce` to specify a default * Use the top-level ``default`` kwarg on :func:`~glom.glom()` In any case, be glad you got this error and not the one it was wrapping! Args: exc (Exception): The error that arose when we tried to access *path*. Typically an instance of KeyError, AttributeError, IndexError, or TypeError, and sometimes others. path (Path): The full Path glom was in the middle of accessing when the error occurred. part_idx (int): The index of the part of the *path* that caused the error. >>> target = {'a': {'b': None}} >>> glom(target, 'a.b.c') Traceback (most recent call last): ... PathAccessError: could not access 'c', part 2 of Path('a', 'b', 'c'), got error: ... """ def __init__(self, exc, path, part_idx): self.exc = exc self.path = path self.part_idx = part_idx def __repr__(self): cn = self.__class__.__name__ return '%s(%r, %r, %r)' % (cn, self.exc, self.path, self.part_idx) def __str__(self): return ('could not access %r, part %r of %r, got error: %r' % (self.path.values()[self.part_idx], self.part_idx, self.path, self.exc))
[docs]class CoalesceError(GlomError): """This :exc:`GlomError` subtype is raised from within a :class:`Coalesce` spec's processing, when none of the subspecs match and no default is provided. The exception object itself keeps track of several values which may be useful for processing: Args: coal_obj (Coalesce): The original failing spec, see :class:`Coalesce`'s docs for details. skipped (list): A list of ignored values and exceptions, in the order that their respective subspecs appear in the original *coal_obj*. path: Like many GlomErrors, this exception knows the path at which it occurred. >>> target = {} >>> glom(target, Coalesce('a', 'b')) Traceback (most recent call last): ... CoalesceError: no valid values found. Tried ('a', 'b') and got (PathAccessError, PathAccessError) ... """ def __init__(self, coal_obj, skipped, path): self.coal_obj = coal_obj self.skipped = skipped self.path = path def __repr__(self): cn = self.__class__.__name__ return '%s(%r, %r, %r)' % (cn, self.coal_obj, self.skipped, self.path) def __str__(self): missed_specs = tuple(self.coal_obj.subspecs) skipped_vals = [v.__class__.__name__ if isinstance(v, self.coal_obj.skip_exc) else '<skipped %s>' % v.__class__.__name__ for v in self.skipped] msg = ('no valid values found. Tried %r and got (%s)' % (missed_specs, ', '.join(skipped_vals))) if self.coal_obj.skip is not _MISSING: msg += ', skip set to %r' % (self.coal_obj.skip,) if self.coal_obj.skip_exc is not GlomError: msg += ', skip_exc set to %r' % (self.coal_obj.skip_exc,) if self.path is not None: msg += ' (at path %r)' % (self.path,) return msg
[docs]class UnregisteredTarget(GlomError): """This :class:`GlomError` subtype is raised when a spec calls for an unsupported action on a target type. For instance, trying to iterate on an non-iterable target: >>> glom(object(), ['a.b.c']) Traceback (most recent call last): ... UnregisteredTarget: target type 'object' not registered for 'iterate', expected one of registered types: (...) It should be noted that this is a pretty uncommon occurrence in production glom usage. See the :ref:`setup-and-registration` section for details on how to avoid this error. An UnregisteredTarget takes and tracks a few values: Args: op (str): The name of the operation being performed ('get' or 'iterate') target_type (type): The type of the target being processed. type_map (dict): A mapping of target types that do support this operation path: The path at which the error occurred. """ def __init__(self, op, target_type, type_map, path): self.op = op self.target_type = target_type self.type_map = type_map self.path = path def __repr__(self): cn = self.__class__.__name__ # <type %r> is because Python 3 inexplicably changed the type # repr from <type *> to <class *> return ('%s(%r, <type %r>, %r, %r)' % (cn, self.op, self.target_type.__name__, self.type_map, self.path)) def __str__(self): if not self.type_map: return ("glom() called without registering any types for operation '%s'. see" " glom.register() or Glommer's constructor for details." % (self.op,)) reg_types = sorted([t.__name__ for t, h in self.type_map.items() if h]) reg_types_str = '()' if not reg_types else ('(%s)' % ', '.join(reg_types)) msg = ("target type %r not registered for '%s', expected one of" " registered types: %s" % (self.target_type.__name__, self.op, reg_types_str)) if self.path: msg += ' (at %r)' % (self.path,) return msg
[docs]class Path(object): """Path objects specify explicit paths when the default ``'a.b.c'``-style general access syntax won't work or isn't desirable. Use this to wrap ints, datetimes, and other valid keys, as well as strings with dots that shouldn't be expanded. >>> target = {'a': {'b': 'c', 'd.e': 'f', 2: 3}} >>> glom(target, Path('a', 2)) 3 >>> glom(target, Path('a', 'd.e')) 'f' Paths can be used to join together other Path objects, as well as :data:`~glom.T` objects: >>> Path(T['a'], T['b']) T['a']['b'] >>> Path(Path('a', 'b'), Path('c', 'd')) Path('a', 'b', 'c', 'd') Paths also support indexing and slicing, with each access returning a new Path object: >>> path = Path('a', 'b', 1, 2) >>> path[0] Path('a') >>> path[-2:] Path(1, 2) """ def __init__(self, *path_parts): if not path_parts: self.path_t = T return if isinstance(path_parts[0], TType): path_t = path_parts[0] offset = 1 else: path_t = T offset = 0 for part in path_parts[offset:]: if isinstance(part, Path): part = part.path_t if isinstance(part, TType): sub_parts = _T_PATHS[part] if sub_parts[0] is not T: raise ValueError('path segment must be path from T, not %r' % sub_parts[0]) i = 1 while i < len(sub_parts): path_t = _t_child(path_t, sub_parts[i], sub_parts[i + 1]) i += 2 else: path_t = _t_child(path_t, 'P', part) self.path_t = path_t @classmethod def from_text(cls, text): """Make a Path from .-delimited text: >>> Path.from_text('a.b.c') Path('a', 'b', 'c') """ return cls(*text.split('.')) def glomit(self, target, scope): # The entrypoint for the Path extension return _t_eval(target, self.path_t, scope) def __len__(self): return (len(_T_PATHS[self.path_t]) - 1) // 2 def __eq__(self, other): if type(other) is Path: return _T_PATHS[self.path_t] == _T_PATHS[other.path_t] elif type(other) is TType: return _T_PATHS[self.path_t] == _T_PATHS[other] return False def __ne__(self, other): return not self == other def values(self): """ Returns a tuple of values referenced in this path. >>> Path(T.a.b, 'c', T['d']).values() ('a', 'b', 'c', 'd') """ cur_t_path = _T_PATHS[self.path_t] return cur_t_path[2::2] def items(self): """ Returns a tuple of (operation, value) pairs. >>> Path(T.a.b, 'c', T['d']).items() (('.', 'a'), ('.', 'b'), ('P', 'c'), ('[', 'd')) """ cur_t_path = _T_PATHS[self.path_t] return tuple(zip(cur_t_path[1::2], cur_t_path[2::2])) def startswith(self, other): if isinstance(other, basestring): other = Path(other) if isinstance(other, Path): other = other.path_t if not isinstance(other, TType): raise TypeError('can only check if Path starts with string, Path or T') o_path = _T_PATHS[other] return _T_PATHS[self.path_t][:len(o_path)] == o_path def from_t(self): '''return the same path but starting from T''' t_path = _T_PATHS[self.path_t] if t_path[0] is S: new_t = TType() _T_PATHS[new_t] = (T,) + t_path[1:] return Path(new_t) return self def __getitem__(self, i): cur_t_path = _T_PATHS[self.path_t] try: step = i.step start = i.start if i.start is not None else 0 stop = i.stop start = (start * 2) + 1 if start >= 0 else (start * 2) + len(cur_t_path) if stop is not None: stop = (stop * 2) + 1 if stop >= 0 else (stop * 2) + len(cur_t_path) except AttributeError: step = 1 start = (i * 2) + 1 if i >= 0 else (i * 2) + len(cur_t_path) if start < 0 or start > len(cur_t_path): raise IndexError('Path index out of range') stop = ((i + 1) * 2) + 1 if i >= 0 else ((i + 1) * 2) + len(cur_t_path) new_t = TType() new_path = cur_t_path[start:stop] if step is not None and step != 1: new_path = tuple(zip(new_path[::2], new_path[1::2]))[::step] new_path = sum(new_path, ()) _T_PATHS[new_t] = (cur_t_path[0],) + new_path return Path(new_t) def __repr__(self): return _format_path(_T_PATHS[self.path_t][1:])
def _format_path(t_path): path_parts, cur_t_path = [], [] i = 0 while i < len(t_path): op, arg = t_path[i], t_path[i + 1] i += 2 if op == 'P': if cur_t_path: path_parts.append(cur_t_path) cur_t_path = [] path_parts.append(arg) else: cur_t_path.append(op) cur_t_path.append(arg) if path_parts and cur_t_path: path_parts.append(cur_t_path) if path_parts or not cur_t_path: return 'Path(%s)' % ', '.join([_format_t(part) if type(part) is list else repr(part) for part in path_parts]) return _format_t(cur_t_path)
[docs]class Literal(object): """Literal objects specify literal values in rare cases when part of the spec should not be interpreted as a glommable subspec. Wherever a Literal object is encountered in a spec, it is replaced with its wrapped *value* in the output. >>> target = {'a': {'b': 'c'}} >>> spec = {'a': 'a.b', 'readability': Literal('counts')} >>> pprint(glom(target, spec)) {'a': 'c', 'readability': 'counts'} Instead of accessing ``'counts'`` as a key like it did with ``'a.b'``, :func:`~glom.glom` just unwrapped the literal and included the value. :class:`~glom.Literal` takes one argument, the literal value that should appear in the glom output. This could also be achieved with a callable, e.g., ``lambda x: 'literal_string'`` in the spec, but using a :class:`~glom.Literal` object adds explicitness, code clarity, and a clean :func:`repr`. """ def __init__(self, value): self.value = value def glomit(self, target, scope): return self.value def __repr__(self): cn = self.__class__.__name__ return '%s(%r)' % (cn, self.value)
[docs]class Spec(object): """Spec objects serve three purposes, here they are, roughly ordered by utility: 1. As a form of compiled or "curried" glom call, similar to Python's built-in :func:`re.compile`. 2. A marker as an object as representing a spec rather than a literal value in certain cases where that might be ambiguous. 3. A way to update the scope within another Spec. In the second usage, Spec objects are the complement to :class:`~glom.Literal`, wrapping a value and marking that it should be interpreted as a glom spec, rather than a literal value. This is useful in places where it would be interpreted as a value by default. (Such as T[key], Call(func) where key and func are assumed to be literal values and not specs.) Args: spec: The glom spec. scope (dict): additional values to add to the scope when evaluating this Spec """ def __init__(self, spec, scope=None): self.spec = spec self.scope = scope or {} def glom(self, target, **kw): scope = dict(self.scope) scope.update(kw.get('scope', {})) kw['scope'] = scope return glom(target, self.spec, **kw) def glomit(self, target, scope): scope.update(self.scope) return scope[glom](target, self.spec, scope) def __repr__(self): cn = self.__class__.__name__ if self.scope: return '%s(%r, scope=%r)' % (cn, self.spec, self.scope) return '%s(%r)' % (cn, self.spec)
[docs]class Coalesce(object): """Coalesce objects specify fallback behavior for a list of subspecs. Subspecs are passed as positional arguments, and keyword arguments control defaults. Each subspec is evaluated in turn, and if none match, a :exc:`CoalesceError` is raised, or a default is returned, depending on the options used. .. note:: This operation may seem very familar if you have experience with `SQL`_ or even `C# and others`_. In practice, this fallback behavior's simplicity is only surpassed by its utility: >>> target = {'c': 'd'} >>> glom(target, Coalesce('a', 'b', 'c')) 'd' glom tries to get ``'a'`` from ``target``, but gets a KeyError. Rather than raise a :exc:`~glom.PathAccessError` as usual, glom *coalesces* into the next subspec, ``'b'``. The process repeats until it gets to ``'c'``, which returns our value, ``'d'``. If our value weren't present, we'd see: >>> target = {} >>> glom(target, Coalesce('a', 'b')) Traceback (most recent call last): ... CoalesceError: no valid values found. Tried ('a', 'b') and got (PathAccessError, PathAccessError) ... Same process, but because ``target`` is empty, we get a :exc:`CoalesceError`. If we want to avoid an exception, and we know which value we want by default, we can set *default*: >>> target = {} >>> glom(target, Coalesce('a', 'b', 'c'), default='d-fault') 'd-fault' ``'a'``, ``'b'``, and ``'c'`` weren't present so we got ``'d-fault'``. Args: subspecs: One or more glommable subspecs default: A value to return if no subspec results in a valid value default_factory: A callable whose result will be returned as a default skip: A value, tuple of values, or predicate function representing values to ignore skip_exc: An exception or tuple of exception types to catch and move on to the next subspec. Defaults to :exc:`GlomError`, the parent type of all glom runtime exceptions. If all subspecs produce skipped values or exceptions, a :exc:`CoalesceError` will be raised. For more examples, check out the :doc:`tutorial`, which makes extensive use of Coalesce. .. _SQL: .. _C# and others: """ def __init__(self, *subspecs, **kwargs): self.subspecs = subspecs self.default = kwargs.pop('default', _MISSING) self.default_factory = kwargs.pop('default_factory', _MISSING) if self.default and self.default_factory: raise ValueError('expected one of "default" or "default_factory", not both') self.skip = kwargs.pop('skip', _MISSING) if self.skip is _MISSING: self.skip_func = lambda v: False elif callable(self.skip): self.skip_func = self.skip elif isinstance(self.skip, tuple): self.skip_func = lambda v: v in self.skip else: self.skip_func = lambda v: v == self.skip self.skip_exc = kwargs.pop('skip_exc', GlomError) if kwargs: raise TypeError('unexpected keyword args: %r' % (sorted(kwargs.keys()),)) def glomit(self, target, scope): skipped = [] for subspec in self.subspecs: try: ret = scope[glom](target, subspec, scope) if not self.skip_func(ret): break skipped.append(ret) except self.skip_exc as e: skipped.append(e) continue else: if self.default is not _MISSING: ret = self.default elif self.default_factory is not _MISSING: ret = self.default_factory() else: raise CoalesceError(self, skipped, scope[Path]) return ret
[docs]class Inspect(object): """The :class:`~glom.Inspect` specifier type provides a way to get visibility into glom's evaluation of a specification, enabling debugging of those tricky problems that may arise with unexpected data. :class:`~glom.Inspect` can be inserted into an existing spec in one of two ways. First, as a wrapper around the spec in question, or second, as an argument-less placeholder wherever a spec could be. :class:`~glom.Inspect` supports several modes, controlled by keyword arguments. Its default, no-argument mode, simply echos the state of the glom at the point where it appears: >>> target = {'a': {'b': {}}} >>> val = glom(target, Inspect('a.b')) # wrapping a spec --- path: ['a.b'] target: {'a': {'b': {}}} output: {} --- Debugging behavior aside, :class:`~glom.Inspect` has no effect on values in the target, spec, or result. Args: echo (bool): Whether to print the path, target, and output of each inspected glom. Defaults to True. recursive (bool): Whether or not the Inspect should be applied at every level, at or below the spec that it wraps. Defaults to False. breakpoint (bool): This flag controls whether a debugging prompt should appear before evaluating each inspected spec. Can also take a callable. Defaults to False. post_mortem (bool): This flag controls whether exceptions should be caught and interactively debugged with :mod:`pdb` on inspected specs. All arguments above are keyword-only to avoid overlap with a wrapped spec. .. note:: Just like ``pdb.set_trace()``, be careful about leaving stray ``Inspect()`` instances in production glom specs. """ def __init__(self, *a, **kw): self.wrapped = a[0] if a else Path() self.recursive = kw.pop('recursive', False) self.echo = kw.pop('echo', True) breakpoint = kw.pop('breakpoint', False) if breakpoint is True: breakpoint = pdb.set_trace if breakpoint and not callable(breakpoint): raise TypeError('breakpoint expected bool or callable, not: %r' % breakpoint) self.breakpoint = breakpoint post_mortem = kw.pop('post_mortem', False) if post_mortem is True: post_mortem = pdb.post_mortem if post_mortem and not callable(post_mortem): raise TypeError('post_mortem expected bool or callable, not: %r' % post_mortem) self.post_mortem = post_mortem def __repr__(self): return '<INSPECT>' def glomit(self, target, scope): # stash the real handler under Inspect, # and replace the child handler with a trace callback scope[Inspect] = scope[glom] scope[glom] = self._trace return scope[glom](target, self.wrapped, scope) def _trace(self, target, spec, scope): if not self.recursive: scope[glom] = scope[Inspect] if self.echo: print('---') print('path: ', scope[Path] + [spec]) print('target:', target) if self.breakpoint: self.breakpoint() try: ret = scope[Inspect](target, self.wrapped, scope) except Exception: if self.post_mortem: self.post_mortem() raise if self.echo: print('output:', ret) print('---') return ret
[docs]class Call(object): """:class:`Call` specifies when a target should be passed to a function, *func*. :class:`Call` is similar to :func:`~functools.partial` in that it is no more powerful than ``lambda`` or other functions, but it is designed to be more readable, with a better ``repr``. Args: func (callable): a function or other callable to be called with the target :class:`Call` combines well with :attr:`~glom.T` to construct objects. For instance, to generate a dict and then pass it to a constructor: >>> class ExampleClass(object): ... def __init__(self, attr): ... self.attr = attr ... >>> target = {'attr': 3.14} >>> glom(target, Call(ExampleClass, kwargs=T)).attr 3.14 This does the same as ``glom(target, lambda target: ExampleClass(**target))``, but it's easy to see which one reads better. .. note:: ``Call`` is mostly for functions. Use a :attr:`~glom.T` object if you need to call a method. """ def __init__(self, func=None, args=None, kwargs=None): if func is None: func = T if not (callable(func) or isinstance(func, (Spec, TType))): raise TypeError('expected func to be a callable or T' ' expression, not: %r' % (func,)) if args is None: args = () if kwargs is None: kwargs = {} self.func, self.args, self.kwargs = func, args, kwargs def glomit(self, target, scope): 'run against the current target' def _eval(t): if type(t) in (Spec, TType): return scope[glom](target, t, scope) return t if type(self.args) is TType: args = _eval(self.args) else: args = [_eval(a) for a in self.args] if type(self.kwargs) is TType: kwargs = _eval(self.kwargs) else: kwargs = {name: _eval(val) for name, val in self.kwargs.items()} return _eval(self.func)(*args, **kwargs) def __repr__(self): cn = self.__class__.__name__ return '%s(%r, args=%r, kwargs=%r)' % (cn, self.func, self.args, self.kwargs)
class TType(object): """``T``, short for "target". A singleton object that enables object-oriented expression of a glom specification. .. note:: ``T`` is a singleton, and does not need to be constructed. Basically, think of ``T`` as your data's stunt double. Everything that you do to ``T`` will be recorded and executed during the :func:`glom` call. Take this example: >>> spec = T['a']['b']['c'] >>> target = {'a': {'b': {'c': 'd'}}} >>> glom(target, spec) 'd' So far, we've relied on the ``'a.b.c'``-style shorthand for access, or used the :class:`~glom.Path` objects, but if you want to explicitly do attribute and key lookups, look no further than ``T``. But T doesn't stop with unambiguous access. You can also call methods and perform almost any action you would with a normal object: >>> spec = ('a', (T['b'].items(), list)) # reviewed below >>> glom(target, spec) [('c', 'd')] A ``T`` object can go anywhere in the spec. As seen in the example above, we access ``'a'``, use a ``T`` to get ``'b'`` and iterate over its ``items``, turning them into a ``list``. You can even use ``T`` with :class:`~glom.Call` to construct objects: >>> class ExampleClass(object): ... def __init__(self, attr): ... self.attr = attr ... >>> target = {'attr': 3.14} >>> glom(target, Call(ExampleClass, kwargs=T)).attr 3.14 On a further note, while ``lambda`` works great in glom specs, and can be very handy at times, ``T`` and :class:`~glom.Call` eliminate the need for the vast majority of ``lambda`` usage with glom. Unlike ``lambda`` and other functions, ``T`` roundtrips beautifully and transparently: >>> T['a'].b['c']('success') T['a'].b['c']('success') ``T``-related access errors raise a :exc:`~glom.PathAccessError` during the :func:`~glom.glom` call. .. note:: While ``T`` is clearly useful, powerful, and here to stay, its semantics are still being refined. Currently, operations beyond method calls and attribute/item access are considered experimental and should not be relied upon. """ __slots__ = ('__weakref__',) def __getattr__(self, name): if name.startswith('__'): raise AttributeError('T instances reserve dunder attributes') return _t_child(self, '.', name) def __getitem__(self, item): if item is UP: newpath = _T_PATHS[self][:-2] if not newpath: return T t = TType() _T_PATHS[t] = _T_PATHS[self][:-2] return t return _t_child(self, '[', item) def __call__(self, *args, **kwargs): return _t_child(self, '(', (args, kwargs)) def __repr__(self): t_path = _T_PATHS[self] return _format_t(t_path[1:], t_path[0]) def __getstate__(self): t_path = _T_PATHS[self] return tuple(('T' if t_path[0] is T else 'S',) + t_path[1:]) def __setstate__(self, state): _T_PATHS[self] = (T if state[0] == 'T' else S,) + state[1:] _T_PATHS = weakref.WeakKeyDictionary() def _t_child(parent, operation, arg): t = TType() _T_PATHS[t] = _T_PATHS[parent] + (operation, arg) return t def _t_eval(target, _t, scope): t_path = _T_PATHS[_t] i = 1 if t_path[0] is T: cur = target elif t_path[0] is S: cur = scope else: raise ValueError('TType instance with invalid root object') while i < len(t_path): op, arg = t_path[i], t_path[i + 1] if type(arg) in (Spec, TType): arg = scope[glom](target, arg, scope) if op == '.': try: cur = getattr(cur, arg) except AttributeError as e: raise PathAccessError(e, Path(_t), i // 2) elif op == '[': try: cur = cur[arg] except (KeyError, IndexError, TypeError) as e: raise PathAccessError(e, Path(_t), i // 2) elif op == 'P': # Path type stuff (fuzzy match) get = scope[TargetRegistry].get_handler('get', cur, path=t_path[2:i+2:2]) try: cur = get(cur, arg) except Exception as e: raise PathAccessError(e, Path(_t), i // 2) elif op == '(': args, kwargs = arg scope[Path] += t_path[2:i+2:2] cur = scope[glom]( target, Call(cur, args, kwargs), scope) # call with target rather than cur, # because it is probably more intuitive # if args to the call "reset" their path # e.g. "T.a" should mean the same thing # in both of these specs: T.a and T.b(T.a) i += 2 return cur T = TType() # target aka Mr. T aka "this" S = TType() # like T, but means grab stuff from Scope, not Target _T_PATHS[T] = (T,) _T_PATHS[S] = (S,) UP = make_sentinel('UP') def _format_t(path, root=T): def kwarg_fmt(kw): if isinstance(kw, str): return kw return repr(kw) prepr = ['T' if root is T else 'S'] i = 0 while i < len(path): op, arg = path[i], path[i + 1] if op == '.': prepr.append('.' + arg) elif op == '[': prepr.append("[%r]" % (arg,)) elif op == '(': args, kwargs = arg prepr.append("(%s)" % ", ".join([repr(a) for a in args] + ["%s=%r" % (kwarg_fmt(k), v) for k, v in kwargs.items()])) elif op == 'P': return _format_path(path) i += 2 return "".join(prepr)
[docs]class CheckError(GlomError): """This :exc:`GlomError` subtype is raised when target data fails to pass a :class:`Check`'s specified validation. An uncaught ``CheckError`` looks like this:: >>> target = {'a': {'b': 'c'}} >>> glom(target, {'b': ('a.b', Check(type=int))}) Traceback (most recent call last): ... CheckError: target at path ['a.b'] failed check, got error: "expected type to be 'int', found type 'str'" If the ``Check`` contains more than one condition, there may be more than one error message. The string rendition of the ``CheckError`` will include all messages. You can also catch the ``CheckError`` and programmatically access messages through the ``msgs`` attribute on the ``CheckError`` instance. .. note:: As of 2018-07-05 (glom v18.2.0), the validation subsystem is still very new. Exact error message formatting may be enhanced in future releases. """ def __init__(self, msgs, check, path): self.msgs = msgs self.check_obj = check self.path = path def __repr__(self): cn = self.__class__.__name__ return '%s(%r, %r, %r)' % (cn, self.msgs, self.check_obj, self.path) def __str__(self): msg = 'target at path %s failed check,' % self.path if self.check_obj.spec is not T: msg += ' subtarget at %r' % (self.check_obj.spec,) if len(self.msgs) == 1: msg += ' got error: %r' % (self.msgs[0],) else: msg += ' got %s errors: %r' % (len(self.msgs), self.msgs) return msg
RAISE = make_sentinel('RAISE') # flag object for "raise on check failure"
[docs]class Check(object): """Check objects are used to make assertions about the target data, and either pass through the data or raise exceptions if there is a problem. If any check condition fails, a :class:`~glom.CheckError` is raised. Args: spec: a sub-spec to extract the data to which other assertions will be checked (defaults to applying checks to the target itself) type: a type or sequence of types to be checked for exact match equal_to: a value to be checked for equality match ("==") validate: a callable or list of callables, each representing a check condition. If one or more return False or raise an exception, the Check will fail. instance_of: a type or sequence of types to be checked with isinstance() one_of: an iterable of values, any of which can match the target ("in") default: an optional default value to replace the value when the check fails (if default is not specified, GlomCheckError will be raised) Aside from *spec*, all arguments are keyword arguments. Each argument, except for *default*, represent a check condition. Multiple checks can be passed, and if all check conditions are left unset, Check defaults to performing a basic truthy check on the value. """ # TODO: the next level of Check would be to play with the Scope to # allow checking to continue across the same level of # dictionary. Basically, collect as many errors as possible before # raising the unified CheckError. def __init__(self, spec=T, **kwargs): self.spec = spec self.default = kwargs.pop('default', RAISE) def _get_arg_val(name, cond, func, val, can_be_empty=True): if val is _MISSING: return () if not is_iterable(val): val = (val,) elif not val and not can_be_empty: raise ValueError('expected %r argument to contain at least one value,' ' not: %r' % (name, val)) for v in val: if not func(v): raise ValueError('expected %r argument to be %s, not: %r' % (name, cond, v)) return val # if there are other common validation functions, maybe a # small set of special strings would work as valid arguments # to validate, too. def truthy(val): return bool(val) validate = kwargs.pop('validate', _MISSING if kwargs else truthy) type_arg = kwargs.pop('type', _MISSING) instance_of = kwargs.pop('instance_of', _MISSING) equal_to = kwargs.pop('equal_to', _MISSING) one_of = kwargs.pop('one_of', _MISSING) if kwargs: raise TypeError('unexpected keyword arguments: %r' % kwargs.keys()) self.validators = _get_arg_val('validate', 'callable', callable, validate) self.instance_of = _get_arg_val('instance_of', 'a type', lambda x: isinstance(x, type), instance_of, False) self.types = _get_arg_val('type', 'a type', lambda x: isinstance(x, type), type_arg, False) if equal_to is not _MISSING: self.vals = (equal_to,) if one_of is not _MISSING: raise TypeError('expected "one_of" argument to be unset when' ' "equal_to" argument is passed') elif one_of is not _MISSING: if not is_iterable(one_of): raise ValueError('expected "one_of" argument to be iterable' ' , not: %r' % one_of) if not one_of: raise ValueError('expected "one_of" to contain at least' ' one value, not: %r' % (one_of,)) self.vals = one_of else: self.vals = () return class _ValidationError(Exception): "for internal use inside of Check only" pass def glomit(self, target, scope): ret = target errs = [] if self.spec is not T: target = scope[glom](target, self.spec, scope) if self.types and type(target) not in self.types: if self.default is not RAISE: return self.default errs.append('expected type to be %r, found type %r' % (self.types[0].__name__ if len(self.types) == 1 else tuple([t.__name__ for t in self.types]), type(target).__name__)) if self.vals and target not in self.vals: if self.default is not RAISE: return self.default if len(self.vals) == 1: errs.append("expected {}, found {}".format(self.vals[0], target)) else: errs.append('expected one of {}, found {}'.format(self.vals, target)) if self.validators: for i, validator in enumerate(self.validators): try: res = validator(target) if res is False: raise self._ValidationError except Exception as e: msg = ('expected %r check to validate target' % getattr(validator, '__name__', None) or ('#%s' % i)) if type(e) is self._ValidationError: if self.default is not RAISE: return self.default else: msg += ' (got exception: %r)' % e errs.append(msg) if self.instance_of and not isinstance(target, self.instance_of): # TODO: can these early returns be done without so much copy-paste? # (early return to avoid potentially expensive or even error-causeing # string formats) if self.default is not RAISE: return self.default errs.append('expected instance of %r, found instance of %r' % (self.instance_of[0].__name__ if len(self.instance_of) == 1 else tuple([t.__name__ for t in self.instance_of]), type(target).__name__)) if errs: # TODO: due to the usage of basic path (not a Path # object), the format can be a bit inconsistent here # (e.g., 'a.b' and ['a', 'b']) raise CheckError(errs, self, scope[Path]) return ret
class _AbstractIterable(_AbstractIterableBase): __metaclass__ = ABCMeta @classmethod def __subclasshook__(cls, C): if C in (str, bytes): return False return callable(getattr(C, "__iter__", None)) def _get_sequence_item(target, index): return target[int(index)] # handlers are 3-arg callables, with args (spec, target, scope) # spec is the first argument for convenience in the case # that the handler is a method of the spec type def _handle_dict(target, spec, scope): ret = type(spec)() # TODO: works for dict + ordereddict, but sufficient for all? for field, subspec in spec.items(): val = scope[glom](target, subspec, scope) if val is SKIP: continue if type(field) in (Spec, TType): field = scope[glom](target, field, scope) ret[field] = val return ret def _handle_list(target, spec, scope): subspec = spec[0] iterate = scope[TargetRegistry].get_handler('iterate', target, path=scope[Path]) try: iterator = iterate(target) except Exception as e: raise TypeError('failed to iterate on instance of type %r at %r (got %r)' % (target.__class__.__name__, Path(*scope[Path]), e)) ret = [] for i, t in enumerate(iterator): val = scope[glom](t, subspec, scope.new_child({Path: scope[Path] + [i]})) if val is SKIP: continue if val is STOP: break ret.append(val) return ret def _handle_tuple(target, spec, scope): res = target for subspec in spec: nxt = scope[glom](res, subspec, scope) if nxt is SKIP: continue if nxt is STOP: break res = nxt if not isinstance(subspec, list): scope[Path] += [getattr(subspec, '__name__', subspec)] return res class TargetRegistry(object): ''' responsible for registration of target types for iteration and attribute walking ''' def __init__(self, register_default_types=True): self._op_type_map = {} self._op_type_tree = {} # see _register_fuzzy_type for details self._op_auto_map = OrderedDict() # op name to function that returns handler function self._register_builtin_ops() if register_default_types: self._register_default_types() return def get_handler(self, op, obj, path=None, raise_exc=True): """for an operation and object **instance**, obj, return the closest-matching handler function, raising UnregisteredTarget if no handler can be found for *obj* (or False if raise_exc=False) """ ret = False obj_type = type(obj) type_map = self.get_type_map(op) if type_map: try: ret = type_map[obj_type] except KeyError: type_tree = self._op_type_tree.get(op, {}) closest = self._get_closest_type(obj, type_tree=type_tree) if closest is None: ret = False else: ret = type_map[closest] if ret is False and raise_exc: raise UnregisteredTarget(op, obj_type, type_map=type_map, path=path) return ret def get_type_map(self, op): try: return self._op_type_map[op] except KeyError: return OrderedDict() def _get_closest_type(self, obj, type_tree): default = None for cur_type, sub_tree in type_tree.items(): if isinstance(obj, cur_type): sub_type = self._get_closest_type(obj, type_tree=sub_tree) ret = cur_type if sub_type is None else sub_type return ret return default def _register_default_types(self): self.register(object) self.register(dict, get=operator.getitem) self.register(list, get=_get_sequence_item) self.register(tuple, get=_get_sequence_item) self.register(_AbstractIterable, iterate=iter) def _register_fuzzy_type(self, op, new_type, _type_tree=None): """Build a "type tree", an OrderedDict mapping registered types to their subtypes The type tree's invariant is that a key in the mapping is a valid parent type of all its children. Order is preserved such that non-overlapping parts of the subtree take precedence by which was most recently added. """ if _type_tree is None: try: _type_tree = self._op_type_tree[op] except KeyError: _type_tree = self._op_type_tree[op] = OrderedDict() registered = False for cur_type, sub_tree in list(_type_tree.items()): if issubclass(cur_type, new_type): sub_tree = _type_tree.pop(cur_type) # mutation for recursion brevity try: _type_tree[new_type][cur_type] = sub_tree except KeyError: _type_tree[new_type] = OrderedDict({cur_type: sub_tree}) registered = True elif issubclass(new_type, cur_type): _type_tree[cur_type] = self._register_fuzzy_type(op, new_type, _type_tree=sub_tree) registered = True if not registered: _type_tree[new_type] = OrderedDict() return _type_tree def register(self, target_type, **kwargs): if not isinstance(target_type, type): raise TypeError('register expected a type, not an instance: %r' % (target_type,)) exact = kwargs.pop('exact', None) new_op_map = dict(kwargs) for op_name in sorted(set(self._op_auto_map.keys()) | set(new_op_map.keys())): cur_type_map = self._op_type_map.setdefault(op_name, OrderedDict()) if op_name in new_op_map: handler = new_op_map[op_name] elif target_type in cur_type_map: handler = cur_type_map[target_type] else: try: handler = self._op_auto_map[op_name](target_type) except Exception as e: raise TypeError('error while determining support for operation' ' "%s" on target type: %s (got %r)' % (op_name, target_type.__name__, e)) if handler is not False and not callable(handler): raise TypeError('expected handler for op "%s" to be' ' callable or False, not: %r' % (op_name, handler)) new_op_map[op_name] = handler for op_name, handler in new_op_map.items(): self._op_type_map[op_name][target_type] = handler if not exact: for op_name in new_op_map: self._register_fuzzy_type(op_name, target_type) return def register_op(self, op_name, auto_func=None, exact=False): """add operations beyond the builtins ('get' and 'iterate' at the time of writing). auto_func is a function that when passed a type, returns a handler associated with op_name if it's supported, or False if it's not. See glom.core.register_op() for the global version used by extensions. """ if not isinstance(op_name, basestring): raise TypeError('expected op_name to be a text name, not: %r' % (op_name,)) if auto_func is None: auto_func = lambda t: False elif not callable(auto_func): raise TypeError('expected auto_func to be callable, not: %r' % (auto_func,)) # determine support for any previously known types known_types = set(sum([list(m.keys()) for m in self._op_type_map.values()], [])) type_map = self._op_type_map.get(op_name, OrderedDict()) type_tree = self._op_type_tree.get(op_name, OrderedDict()) for t in known_types: if t in type_map: continue try: handler = auto_func(t) except Exception as e: raise TypeError('error while determining support for operation' ' "%s" on target type: %s (got %r)' % (op_name, t.__name__, e)) if handler is not False and not callable(handler): raise TypeError('expected handler for op "%s" to be' ' callable or False, not: %r' % (op_name, handler)) type_map[t] = handler if not exact: for t in known_types: self._register_fuzzy_type(op_name, t, _type_tree=type_tree) self._op_type_map[op_name] = type_map self._op_type_tree[op_name] = type_tree self._op_auto_map[op_name] = auto_func def _register_builtin_ops(self): def _get_iterable_handler(type_obj): return iter if callable(getattr(type_obj, '__iter__', None)) else False self.register_op('iterate', _get_iterable_handler) self.register_op('get', lambda _: getattr) _DEFAULT_SCOPE = ChainMap({})
[docs]def glom(target, spec, **kwargs): """Access or construct a value from a given *target* based on the specification declared by *spec*. Accessing nested data, aka deep-get: >>> target = {'a': {'b': 'c'}} >>> glom(target, 'a.b') 'c' Here the *spec* was just a string denoting a path, ``'a.b.``. As simple as it should be. The next example shows how to use nested data to access many fields at once, and make a new nested structure. Constructing, or restructuring more-complicated nested data: >>> target = {'a': {'b': 'c', 'd': 'e'}, 'f': 'g', 'h': [0, 1, 2]} >>> spec = {'a': 'a.b', 'd': 'a.d', 'h': ('h', [lambda x: x * 2])} >>> output = glom(target, spec) >>> pprint(output) {'a': 'c', 'd': 'e', 'h': [0, 2, 4]} ``glom`` also takes a keyword-argument, *default*. When set, if a ``glom`` operation fails with a :exc:`GlomError`, the *default* will be returned, very much like :meth:`dict.get()`: >>> glom(target, 'a.xx', default='nada') 'nada' The *skip_exc* keyword argument controls which errors should be ignored. >>> glom({}, lambda x: 100.0 / len(x), default=0.0, skip_exc=ZeroDivisionError) 0.0 Args: target (object): the object on which the glom will operate. spec (object): Specification of the output object in the form of a dict, list, tuple, string, other glom construct, or any composition of these. default (object): An optional default to return in the case an exception, specified by *skip_exc*, is raised. skip_exc (Exception): An optional exception or tuple of exceptions to ignore and return *default* (None if omitted). If *skip_exc* and *default* are both not set, glom raises errors through. scope (dict): Additional data that can be accessed via S inside the glom-spec. It's a small API with big functionality, and glom's power is only surpassed by its intuitiveness. Give it a whirl! """ # TODO: check spec up front default = kwargs.pop('default', None if 'skip_exc' in kwargs else _MISSING) skip_exc = kwargs.pop('skip_exc', () if default is _MISSING else GlomError) scope = _DEFAULT_SCOPE.new_child({ Path: kwargs.pop('path', []), Inspect: kwargs.pop('inspector', None) }) scope.update(kwargs.pop('scope', {})) if kwargs: raise TypeError('unexpected keyword args: %r' % sorted(kwargs.keys())) try: ret = _glom(target, spec, scope) except skip_exc: if default is _MISSING: raise ret = default return ret
def _glom(target, spec, scope): scope = scope.new_child() scope[T] = target scope[Spec] = spec if isinstance(spec, TType): # must go first, due to callability return _t_eval(target, spec, scope) elif callable(getattr(spec, 'glomit', None)): return spec.glomit(target, scope) elif isinstance(spec, dict): return _handle_dict(target, spec, scope) elif isinstance(spec, list): return _handle_list(target, spec, scope) elif isinstance(spec, tuple): return _handle_tuple(target, spec, scope) elif isinstance(spec, basestring): return Path.from_text(spec).glomit(target, scope) elif callable(spec): return spec(target) raise TypeError('expected spec to be dict, list, tuple, callable, string,' ' or other Spec-like type, not: %r' % (spec,)) _DEFAULT_SCOPE.update({ glom: _glom, TargetRegistry: TargetRegistry(register_default_types=True), })
[docs]def register(target_type, **kwargs): """Register *target_type* so :meth:`~Glommer.glom()` will know how to handle instances of that type as targets. Args: target_type (type): A type expected to appear in a glom() call target get (callable): A function which takes a target object and a name, acting as a default accessor. Defaults to :func:`getattr`. iterate (callable): A function which takes a target object and returns an iterator. Defaults to :func:`iter` if *target_type* appears to be iterable. exact (bool): Whether or not to match instances of subtypes of *target_type*. .. note:: The module-level :func:`register()` function affects the module-level :func:`glom()` function's behavior. If this global effect is undesirable for your application, or you're implementing a library, consider instantiating a :class:`Glommer` instance, and using the :meth:`~Glommer.register()` and :meth:`Glommer.glom()` methods instead. """ _DEFAULT_SCOPE[TargetRegistry].register(target_type, **kwargs) return
def register_op(op_name, **kwargs): """For extension authors needing to add operations beyond the builtin 'get' and 'iterate' to the default scope. See TargetRegistry for more details. """ _DEFAULT_SCOPE[TargetRegistry].register_op(op_name, **kwargs) return
[docs]class Glommer(object): """All the wholesome goodness that it takes to make glom work. This type mostly serves to encapsulate the type registration context so that advanced uses of glom don't need to worry about stepping on each other's toes. Glommer objects are lightweight and, once instantiated, provide the :func:`glom()` method we know and love: >>> glommer = Glommer() >>> glommer.glom({}, 'a.b.c', default='d') 'd' >>> Glommer().glom({'vals': list(range(3))}, ('vals', len)) 3 Instances also provide :meth:`~Glommer.register()` method for localized control over type handling. Args: register_default_types (bool): Whether or not to enable the handling behaviors of the default :func:`glom()`. These default actions include dict access, list and iterable iteration, and generic object attribute access. Defaults to True. """ def __init__(self, **kwargs): register_default_types = kwargs.pop('register_default_types', True) scope = kwargs.pop('scope', _DEFAULT_SCOPE) # this "freezes" the scope in at the time of construction self.scope = ChainMap(dict(scope)) self.scope[TargetRegistry] = TargetRegistry(register_default_types=register_default_types) def register(self, target_type, **kwargs): """Register *target_type* so :meth:`~Glommer.glom()` will know how to handle instances of that type as targets. Args: target_type (type): A type expected to appear in a glom() call target get (callable): A function which takes a target object and a name, acting as a default accessor. Defaults to :func:`getattr`. iterate (callable): A function which takes a target object and returns an iterator. Defaults to :func:`iter` if *target_type* appears to be iterable. exact (bool): Whether or not to match instances of subtypes of *target_type*. .. note:: The module-level :func:`register()` function affects the module-level :func:`glom()` function's behavior. If this global effect is undesirable for your application, or you're implementing a library, consider instantiating a :class:`Glommer` instance, and using the :meth:`~Glommer.register()` and :meth:`Glommer.glom()` methods instead. """ exact = kwargs.pop('exact', False) self.scope[TargetRegistry].register(target_type, exact=exact, **kwargs) return def glom(self, target, spec, **kwargs): return glom(target, spec, scope=self.scope, **kwargs)
"""TODO: * "Restructuring Data" / "Restructured Data" * More subspecs * Inspect - mostly done, but performance checking * Specifier types for all the shorthands (e.g., Assign() for {}, Iterate() for []), allows adding more options in situations that need them. (Call and Target have better aesthetics and repr compared to lambdas, but are otherwise no more capable) * Call * If callable is not intrinsically sufficient for good error reporting, make whatever method it has compatible with the _glom() signature * skip_exc and default arguments to Call, like glom(), for easy try/except * Target * Effectively a path, but with an unambiguous getitem/getattr. (should Path and Target merge??) * Path note: path is ambiguous wrt what access is performed (getitem or getattr), should this be rectified, or is it ok to have TARGET be a more powerful alternative? * More supported target types * Django and SQLAlchemy Models and QuerySets * API for (bypassing) registering known 3rd party integrations like the above * Top-level option to collect all the errors instead of just the first. * This will probably require another context object in addition to inspector and path. * check_spec / audit_spec * Forward check all types (remap?) * Call(func) <- func must take exactly one argument and have the rest fulfilled by args/kwargs * lambdas must also take one argument * empty coalesces? * stray Inspect objects * testing todo: properties that raise exception, other operators that raise exceptions. * Inspect stuff should come out on stderr ## Django models registration: glom.register(django.db.models.Manager, iterate=lambda m: m.all()) glom.register(django.db.models.QuerySet, iterate=lambda qs: qs.all()) * Support unregistering target types * Eventually: Support registering handlers for new spec types in the main glom function. allows users to handle types beyond the glom builtins. Will require really defining the function interface for what a glom takes; currently: target, spec, _path, _inspect. * What to do with empty list and empty tuple (in spec)? * Flag (and exception type) to gather all errors, instead of raising the first * Contact example glom(contact, { 'name': 'name', # simple get-attr 'primary_email': '', # multi-level get-attr 'emails': ('email_set', ['email']), # get-attr + sequence unpack + fetch one attr 'roles': ('vendor_roles', [{'role': 'role'}]), # get-attr + sequence unpack + sub-glom }) """