Source code for sunpy.util.metadata

This module provides a generalized dictionary class that deals with header
parsing, normalization, and maintaining coherence between keys and keycomments.
from collections import OrderedDict, namedtuple
from import Mapping

__all__ = ['MetaDict']

ModifiedItem = namedtuple('ModifiedItem', ['original', 'current'])
ModifiedItem.__repr__ = lambda t: f"(original={t.original}, current={t.current})"

[docs]class MetaDict(OrderedDict): """ A class to hold metadata associated with a `` derivative. This class handles everything in lower case. This allows case insensitive indexing. If the key 'keycomments' exists, its value must be a dictionary mapping keys in the :class:`MetaDict` to their comments. The casing of keys in the keycomments dictionary is not significant. If a key is removed from the :class:`MetaDict`, it will also be removed from the keycomments dictionary. Additionally, any extraneous keycomments will be removed when the :class:`MetaDict` is instantiated. Parameters ---------- save_original : bool, optional If `True` (the default), a copy of the original metadata will be saved to the `original_meta` property. Note that this keyword argument is required as an implementation detail to avoid recursion when saving the original contents. """ def __init__(self, *args, save_original=True): # Store all keys as lower-case to allow for case-insensitive indexing # OrderedDict can be instantiated from a list of lists or a tuple of tuples tags = dict() if args: args = list(args) adict = args[0] if isinstance(adict, MetaDict): self._original_meta = adict._original_meta if isinstance(adict, list) or isinstance(adict, tuple): items = adict elif isinstance(adict, Mapping): # Cast to a dict here, since a Mapping doesn't have to define # a .items() method (but has enough methods to be converted to # a dict) items = dict(adict).items() else: raise TypeError(f"Can not create a MetaDict from this input of type {type(adict)}") self._check_str_keys(items) tags = OrderedDict((k.lower(), v) for k, v in items) args[0] = tags super().__init__(*args) # Use `copy=True` to avoid mutating the caller's keycomments # dictionary (if they provided one). self._prune_keycomments(copy=True) if save_original and not hasattr(self, '_original_meta'): self._original_meta = MetaDict(*args, save_original=False) def __str__(self): return '\n'.join([f'{key}: {item}' for key, item in self.items()]) # Deliberately a property to prevent external modification @property def original_meta(self): """ A copy of the dictionary from when it was initialised. """ return self._original_meta @property def added_items(self): """ Items added since initialisation. """ return {k: self[k] for k in set(self) - set(self.original_meta)} @property def removed_items(self): """ Items removed since initialisation. """ return {k: self.original_meta[k] for k in set(self.original_meta) - set(self)} @property def modified_items(self): """ Items modified since initialisation. This is a mapping from ``key`` to ``[original_value, current_value]``. """ keys = set(self).intersection(set(self.original_meta)) return {k: ModifiedItem(self.original_meta[k], self[k]) for k in keys if self[k] != self.original_meta[k]}
[docs] def copy(self): """ Shallow copies this instance. """ copied = super().copy() # By default the above line will overwrite original_meta, so manually re-instate it copied._original_meta = self.original_meta return copied
@staticmethod def _check_str_keys(items): bad_keys = [] for k, v in items: if not isinstance(k, str): bad_keys.append(str(k)) if len(bad_keys): raise ValueError('All MetaDict keys must be strings, ' 'found the following non-compliant keys: ' + ', '.join(bad_keys)) def _prune_keycomments(self, copy=False): """ Remove keycomments for keys that are not contained in the MetaDict. Parameters ---------- copy : `bool`, optional Make a copy of the current keycomments dict before removing keys. """ if 'keycomments' not in self: return keycomments = self['keycomments'] if not isinstance(keycomments, dict): raise TypeError( "'keycomments' key must have a value of type `dict`. Found " "the following type: %r" % type(keycomments)) if copy: keycomments = keycomments.copy() for key in list(keycomments.keys()): if key not in self: del keycomments[key] self['keycomments'] = keycomments def __contains__(self, key): """ Override ``__contains__``. """ return OrderedDict.__contains__(self, key.lower()) def __getitem__(self, key): """ Override ``[]`` indexing. """ return OrderedDict.__getitem__(self, key.lower()) def __setitem__(self, key, value): """ Override ``[]`` indexing. """ return OrderedDict.__setitem__(self, key.lower(), value) # Note: `OrderedDict.popitem()` does not need to be overridden to prune # keycomments because it calls `__delitem__` internally. def __delitem__(self, key): """ Override ``del dict[key]`` key deletion. """ OrderedDict.__delitem__(self, key.lower()) self._prune_keycomments()
[docs] def item_hash(self): """ Create a hash based on the stored items. This relies on all the items themselves being hashable. For this reason the 'keycomments' item, which is a dict, is excluded from the hash. If creating the hash fails, returns `None`. """ self_copy = self.copy() self_copy.pop('keycomments', None) try: return hash(frozenset(self_copy.items())) except Exception: return
[docs] def get(self, key, default=None): """ Override ``.get()`` indexing. """ return OrderedDict.get(self, key.lower(), default)
[docs] def has_key(self, key): """ Override ``.has_key()`` to perform case-insensitively. """ return key.lower() in self
[docs] def pop(self, key, default=None): """ Override ``.pop()`` to perform case-insensitively. """ has_key = key in self result = OrderedDict.pop(self, key.lower(), default) if has_key: self._prune_keycomments() return result
[docs] def update(self, d2): """ Override ``.update()`` to perform case-insensitively. """ return OrderedDict.update(self, OrderedDict((k.lower(), v) for k, v in d2.items()))
[docs] def setdefault(self, key, default=None): """ Override ``.setdefault()`` to perform case-insensitively. """ return OrderedDict.setdefault(self, key.lower(), default)