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318 lines
9.5 KiB
Python
318 lines
9.5 KiB
Python
"""
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Parent of all field classes in :mod:`hachoir.field`.
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"""
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from hachoir.stream import InputFieldStream
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from hachoir.core.log import Logger
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from hachoir.core.tools import makePrintable
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from weakref import ref as weakref_ref
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class FieldError(Exception):
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"""
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Error raised by a :class:`Field`
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"""
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pass
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def joinPath(path, name):
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if path != "/":
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return "/".join((path, name))
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else:
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return "/%s" % name
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class MissingField(KeyError, FieldError):
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def __init__(self, field, key):
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KeyError.__init__(self)
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self.field = field
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self.key = key
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def __str__(self):
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return 'Can\'t get field "%s" from %s' % (self.key, self.field.path)
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class Field(Logger):
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static_size = None
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"""(optional) Helper to compute field size.
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May have types:
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None: field size is computed dynamically.
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int: field size, in bits.
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callable: function that receives the same arguments as the constructor,
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without ``parent``.
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"""
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is_field_set = False
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"""bool: True if this field contains other fields (ie. is a field set),
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False otherwise.
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"""
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def __init__(self, parent, name, size=None, description=None):
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"""Set default class attributes, set right address if None address is
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given.
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Args:
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parent (Field): Parent field of this field
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name (str): The name of the field, it must be unique in `parent`. If
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it ends with `[]`, end will be replaced with "[new_id]" (eg.
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"raw[]" becomes "raw[0]", next will be "raw[1]", and then
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"raw[2]", etc.)
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size (int, optional): Size of the field in bits. If `None` then it
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will be computed later.
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address (int, optional): Address in bit relative to the parent
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absolute address.
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description (str, optional): String description
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"""
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assert issubclass(parent.__class__, Field)
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assert (size is None) or (0 <= size)
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self._parent = parent
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if not name:
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raise ValueError("empty field name")
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self._name = name
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self._address = parent.nextFieldAddress()
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self._size = size
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self._description = description
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def _logger(self):
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return self.path
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def createDescription(self):
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"""Override in derived classes to provide :attr:`description`."""
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return ""
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@property
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def description(self):
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"""str: Informal description of this field. Cached.
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The description of a field may provide a general summary of its usage
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or for field sets it can be used to give a short indication of the
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contents without having to expand the node.
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"""
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if self._description is None:
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try:
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self._description = self.createDescription()
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if isinstance(self._description, str):
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self._description = makePrintable(
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self._description, "ISO-8859-1")
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except Exception as err:
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self.error("Error getting description: " + str(err))
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self._description = ""
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return self._description
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def __str__(self):
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"""Alias for :attr:`display`."""
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return self.display
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def __repr__(self):
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return "<%s path=%r, address=%s, size=%s>" % (
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self.__class__.__name__, self.path, self._address, self._size)
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def hasValue(self):
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"""bool: Check if field has a value."""
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return self.value is not None
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def createValue(self):
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"""Override in derived classes to provide :attr:`value`."""
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raise NotImplementedError()
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@property
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def value(self):
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"""Value of field."""
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try:
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return self.__value
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except AttributeError:
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try:
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self.__value = self.createValue()
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except Exception as err:
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self.error("Unable to create value: %s" % str(err))
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self.__value = None
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return self.__value
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@property
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def parent(self):
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"""GenericFieldSet: Parent of this field."""
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return self._parent
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def createDisplay(self):
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"""Override in derived classes to provide :attr:`display`."""
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return str(self.value)
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@property
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def display(self):
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"""str: Short, human-friendly string representing field contents."""
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try:
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return self.__display
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except AttributeError:
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try:
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self.__display = self.createDisplay()
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except Exception as err:
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self.error("Unable to create display: %s" % err)
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self.__display = ""
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return self.__display
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def createRawDisplay(self):
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value = self.value
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if isinstance(value, str):
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return makePrintable(value, "ASCII")
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else:
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return str(value)
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@property
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def raw_display(self):
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"""str: Represents raw field content"""
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try:
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return self.__raw_display
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except AttributeError:
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try:
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self.__raw_display = self.createRawDisplay()
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except Exception as err:
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self.error("Unable to create raw display: %s" % err)
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self.__raw_display = ""
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return self.__raw_display
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@property
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def name(self):
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"""str: Field name, unique in its parent field set list."""
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return self._name
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@property
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def index(self):
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"""int: index of the field in parent field set, starting from 0."""
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if not self._parent:
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return None
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return self._parent.getFieldIndex(self)
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@property
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def path(self):
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"""str: Full path of this field starting from the root field."""
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if not self._parent:
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return '/'
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names = []
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field = self
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while field is not None:
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names.append(field._name)
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field = field._parent
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names[-1] = ''
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return '/'.join(reversed(names))
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@property
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def address(self):
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"""int: Relative address to parent address, in bits."""
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return self._address
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@property
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def absolute_address(self):
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"""int: Absolute address (from beginning of stream), in bits."""
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address = self._address
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current = self._parent
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while current:
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address += current._address
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current = current._parent
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return address
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@property
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def size(self):
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"""int: Size of this field, in bits. Cached."""
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return self._size
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def _getField(self, name, const):
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if name.strip("."):
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return None
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field = self
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for index in range(1, len(name)):
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field = field._parent
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if field is None:
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break
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return field
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def getField(self, key, const=True):
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"""
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Args:
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key (str): relative or absolute path for the desired field.
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const (bool): For field sets, whether to consume additional input to
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find a matching field.
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Returns:
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Field: The field matching the provided path.
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"""
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if key:
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if key[0] == "/":
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if self._parent:
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current = self._parent.root
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else:
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current = self
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if len(key) == 1:
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return current
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key = key[1:]
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else:
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current = self
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for part in key.split("/"):
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field = current._getField(part, const)
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if field is None:
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raise MissingField(current, part)
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current = field
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return current
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raise KeyError("Key must not be an empty string!")
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def __getitem__(self, key):
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"""Alias for :meth:`getField`, with ``const=False``"""
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return self.getField(key, False)
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def __contains__(self, key):
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"""Check whether a field set contains the provided field.
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Args:
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key (str): The path to the field.
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Returns:
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bool
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"""
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try:
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return self.getField(key, False) is not None
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except FieldError:
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return False
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def _createInputStream(self, **args):
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"""Override in derived classes to provide the input stream returned by
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:meth:`getSubIStream`.
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Returns:
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InputFieldStream
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"""
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assert self._parent
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return InputFieldStream(self, **args)
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def getSubIStream(self):
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"""
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Returns:
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InputFieldStream: an input stream containing the field content.
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"""
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if hasattr(self, "_sub_istream"):
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stream = self._sub_istream()
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else:
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stream = None
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if stream is None:
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stream = self._createInputStream()
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self._sub_istream = weakref_ref(stream)
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return stream
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def setSubIStream(self, createInputStream):
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"""
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Args:
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createInputStream (``callback(cis, **args)``): Function to use in place of
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:meth:`_createInputStream`. Receives the previous value of
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``_createInputStream`` as its first argument, for chaining.
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"""
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cis = self._createInputStream
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self._createInputStream = lambda **args: createInputStream(cis, **args)
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def __bool__(self):
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"""Method called by code like "if field: (...)".
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Always returns True
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"""
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return True
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def getFieldType(self):
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return self.__class__.__name__
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