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
  value.

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

"""

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

PY2 = (sys.version_info[0] == 2)
if PY2:
    _AbstractIterableBase = object
else:
    basestring = str
    _AbstractIterableBase = ABCMeta('_AbstractIterableBase', (object,), {})


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

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

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

"""


[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. path_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', index 2 in path Path('a', 'b', 'c'), got error: ... """ def __init__(self, exc, path, path_idx): self.exc = exc self.path = path self.path_idx = path_idx def __repr__(self): cn = self.__class__.__name__ return '%s(%r, %r, %r)' % (cn, self.exc, self.path, self.path_idx) def __str__(self): return ('could not access %r, index %r in path %r, got error: %r' % (self.path[self.path_idx], self.path_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__ return ('%s(%r, %r, %r, %r)' % (cn, self.op, self.target_type, self.type_map, self.path)) def __str__(self): if not self.type_map: return ("glom() called without registering any types. see glom.register()" " or Glommer's constructor for details.") reg_types = sorted([t.__name__ for t, h in self.type_map.items() if getattr(h, self.op, None)]) 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
class TargetHandler(object): """The TargetHandler is a construct used internally to register general actions on types of targets. The logic for matching a target to its handler based on type is in :meth:`Glommer._get_handler()`. """ def __init__(self, type_obj, get=None, iterate=None): self.type = type_obj if iterate is None: if callable(getattr(type_obj, '__iter__', None)): iterate = iter else: iterate = False if iterate is not False and not callable(iterate): raise ValueError('expected iterable type or callable for iterate, not: %r' % iterate) self.iterate = iterate if get is None: get = getattr if get is not False and not callable(get): raise ValueError('expected callable for get, not: %r' % (get,)) self.get = get
[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' """ def __init__(self, *path_parts): self.path_parts = list(path_parts) def append(self, part): self.path_parts.append(part) def __getitem__(self, idx): return self.path_parts.__getitem__(idx) def __repr__(self): cn = self.__class__.__name__ return '%s(%s)' % (cn, ', '.join([repr(p) for p in self.path_parts]))
[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 __repr__(self): cn = self.__class__.__name__ return '%s(%r)' % (cn, self.value)
class Spec(object): """Spec objects are the complement to Literals, wrapping a value and marking that it should be interpreted as a glom spec, rather than a literal value in places where it would be interpreted as a value by defualt. (Such as T[key], Call(func) where key and func are assumed to be literal values and not specs.) Args: value: The glom spec. """ def __init__(self, value): self.value = value def __repr__(self): cn = self.__class__.__name__ return '%s(%r)' % (cn, self.value)
[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 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: https://en.wikipedia.org/w/index.php?title=Null_(SQL)&oldid=833093792#COALESCE .. _C# and others: https://en.wikipedia.org/w/index.php?title=Null_coalescing_operator&oldid=839493322#C# """ def __init__(self, *subspecs, **kwargs): self.subspecs = subspecs self.default = kwargs.pop('default', _MISSING) 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()),))
[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>'
[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, args=None, kwargs=None): if not callable(func): raise TypeError('Call constructor expected func to be a callable,' ' not: %r' % func) if args is None: args = () if kwargs is None: kwargs = {} if not (callable(func) or isinstance(func, _TType)): raise TypeError('func must be a callable or child of T') self.func, self.args, self.kwargs = func, args, kwargs def __call__(self, target, path, inspector, recurse): 'run against the current target' def eval(t): if type(t) in (Spec, _TType): return recurse(target, t, path, inspector) 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): return 'Call(%r, args=%r, kwargs=%r)' % (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') .. 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. Error types and messages are also being rationalized to match those of :class:`glom.Path`. """ __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): return "T" + _path_fmt(_T_PATHS[self]) _T_PATHS = weakref.WeakKeyDictionary() def _t_child(parent, operation, arg): t = _TType() _T_PATHS[t] = _T_PATHS[parent] + (operation, arg) return t # TODO: merge _t_eval with Path access somewhat and remove these exceptions. # T should be a valid path segment, we just need to keep path/path_idx up to date on the PAE class GlomAttributeError(GlomError, AttributeError): pass class GlomKeyError(GlomError, KeyError): pass class GlomIndexError(GlomError, IndexError): pass class GlomTypeError(GlomError, TypeError): pass def _path_fmt(path): def kwarg_fmt(kw): if isinstance(kw, str): return kw return repr(kw) prepr = [] i = 0 # TODO: % not format() while i < len(path): op, arg = path[i], path[i + 1] if op == '.': prepr.append('.' + arg) elif op == '[': prepr.append("[{0!r}]".format(arg)) elif op == '(': args, kwargs = arg prepr.append("({})".format( ", ".join( [repr(a) for a in args] + ["{}={}".format(kwarg_fmt(k), repr(v)) for k, v in kwargs.items()]))) i += 2 return "".join(prepr) def _t_eval(_t, target, path, inspector, recurse): t_path = _T_PATHS[_t] i = 0 cur = target while i < len(t_path): op, arg = t_path[i], t_path[i + 1] if type(arg) in (Spec, _TType): arg = recurse(target, arg, path, inspector) if op == '.': cur = getattr(cur, arg, _MISSING) if cur is _MISSING: raise GlomAttributeError(_path_fmt(t_path[:i+2])) elif op == '[': try: cur = cur[arg] except KeyError as e: path = _path_fmt(t_path[:i+2]) raise GlomKeyError(path) except IndexError: raise GlomIndexError(_path_fmt(t_path[:i+2])) except TypeError: raise GlomTypeError(_path_fmt(t_path[:i+2])) elif op == '(': args, kwargs = arg cur = recurse( # TODO: mutate path correctly target, Call(cur, args, kwargs), path, inspector) # 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" _T_PATHS[T] = () UP = make_sentinel('UP') 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)]
[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, register_default_types=True): self._type_map = OrderedDict() self._type_tree = OrderedDict() # see _register_fuzzy_type for details if register_default_types: self._register_default_types() self._unreg_handler = TargetHandler(None, get=False, iterate=False) return def _get_handler(self, obj): "return the closest-matching type config for an object *instance*, obj" try: return self._type_map[type(obj)] except KeyError: pass closest = self._get_closest_type(obj) if closest is None: return self._unreg_handler return self._type_map[closest] def _get_closest_type(self, obj, _type_tree=None): type_tree = _type_tree if _type_tree is not None else self._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, operator.getitem) self.register(list, _get_sequence_item) self.register(tuple, _get_sequence_item) self.register(_AbstractIterable, iterate=iter) def _register_fuzzy_type(self, 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. """ type_tree = _type_tree if _type_tree is not None else self._type_tree 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(new_type, _type_tree=sub_tree) registered = True if not registered: type_tree[new_type] = OrderedDict() return type_tree def register(self, target_type, get=None, iterate=None, exact=False): """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. """ if not isinstance(target_type, type): raise TypeError('register expected a type, not an instance: %r' % (target_type,)) self._type_map[target_type] = TargetHandler(target_type, get=get, iterate=iterate) if not exact: self._register_fuzzy_type(target_type) return def _get_path(self, target, path): try: parts = path.split('.') except (AttributeError, TypeError): parts = getattr(path, 'path_parts', None) if parts is None: raise TypeError('path expected str or Path object, not: %r' % path) cur, val = target, target for i, part in enumerate(parts): handler = self._get_handler(cur) if not handler.get: raise UnregisteredTarget('get', type(target), self._type_map, path=path[:i]) try: val = handler.get(cur, part) except Exception as e: raise PathAccessError(e, parts, i) cur = val return val def glom(self, 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. 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) path = kwargs.pop('path', []) inspector = kwargs.pop('inspector', None) if kwargs: raise TypeError('unexpected keyword args: %r' % sorted(kwargs.keys())) try: ret = self._glom(target, spec, path=path, inspector=inspector) except skip_exc: if default is _MISSING: raise ret = default return ret def _glom(self, target, spec, path, inspector): # TODO: de-recursivize this # TODO: rearrange the branching below by frequency of use # recursive self._glom() calls should pass path=path to elide the current # step, otherwise add the current spec in some fashion next_inspector = inspector if (inspector and inspector.recursive) else None if inspector: if inspector.echo: print('---') print('path: ', path + [spec]) print('target:', target) if inspector.breakpoint: inspector.breakpoint() if isinstance(spec, Inspect): try: ret = self._glom(target, spec.wrapped, path=path, inspector=spec) except Exception: if spec.post_mortem: spec.post_mortem() raise elif isinstance(spec, dict): ret = type(spec)() # TODO: works for dict + ordereddict, but sufficient for all? for field, subspec in spec.items(): val = self._glom(target, subspec, path=path, inspector=next_inspector) if val is OMIT: continue ret[field] = val elif isinstance(spec, list): subspec = spec[0] handler = self._get_handler(target) if not handler.iterate: raise UnregisteredTarget('iterate', type(target), self._type_map, path=path) try: iterator = handler.iterate(target) except TypeError as te: raise TypeError('failed to iterate on instance of type %r at %r (got %r)' % (target.__class__.__name__, Path(*path), te)) ret = [] for i, t in enumerate(iterator): val = self._glom(t, subspec, path=path + [i], inspector=inspector) if val is OMIT: continue ret.append(val) elif isinstance(spec, tuple): res = target for subspec in spec: res = self._glom(res, subspec, path=path, inspector=next_inspector) next_inspector = subspec if (isinstance(subspec, Inspect) and subspec.recursive) else next_inspector if not isinstance(subspec, list): path = path + [getattr(subspec, '__name__', subspec)] ret = res elif isinstance(spec, _TType): # NOTE: must come before callable b/c T is also callable ret = _t_eval(spec, target, path, inspector, self._glom) elif isinstance(spec, Call): ret = spec(target, path, inspector, self._glom) elif callable(spec): ret = spec(target) elif isinstance(spec, (basestring, Path)): try: ret = self._get_path(target, spec) except PathAccessError as pae: pae.path = Path(*(path + list(pae.path))) pae.path_idx += len(path) raise elif isinstance(spec, Coalesce): skipped = [] for subspec in spec.subspecs: try: ret = self._glom(target, subspec, path=path, inspector=next_inspector) if not spec.skip_func(ret): break skipped.append(ret) except spec.skip_exc as e: skipped.append(e) continue else: if spec.default is not _MISSING: ret = spec.default else: raise CoalesceError(spec, skipped, path) elif isinstance(spec, Literal): ret = spec.value elif isinstance(spec, Spec): # TODO: this could be switched to a while loop at the top for # performance, but don't want to mess around too much yet # while(type(target) is Spec): target = target.value ret = self._glom(target, spec.value, path=path, inspector=inspector) else: raise TypeError('expected spec to be dict, list, tuple,' ' callable, string, or other specifier type,' ' not: %r'% spec) if inspector and inspector.echo: print('output:', ret) print('---') return ret
_DEFAULT = Glommer(register_default_types=True) glom = _DEFAULT.glom register = _DEFAULT.register pass # this line prevents the docstring below from attaching to register """TODO: * "Restructuring Data" / "Restructured Data" * More subspecs * Inspect - mostly done, but performance checking * Check() - wraps a subspec, performing checking on its return. e.g., Check('a.b.c', type=int, value=1, action='raise') # action='omit' maybe also supported, other actions? * 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': 'primary_email.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 }) """