Module `fpdf.syntax`

Classes & functions that represent core elements of the PDF syntax

Most of what happens in a PDF happens in objects, which are formatted like so:

3 0 obj
<</Type /Page
/Parent 1 0 R
/Resources 2 0 R
/Contents 4 0 R>>
endobj

The first line says that this is the third object in the structure of the document.

There are 8 kinds of objects (Adobe Reference, 51):

Boolean values
Integer and real numbers
Strings
Names
Arrays
Dictionaries
Streams
The null object

The << in the second line and the >> in the line preceding endobj denote that it is a dictionary object. Dictionaries map Names to other objects.

Names are the strings preceded by /, valid Names do not have to start with a capital letter, they can be any ascii characters, # and two characters can escape non-printable ascii characters, described on page 57.

3 0 obj means what follows here is the third object, but the name Type (represented here by /Type) is mapped to an indirect object reference: 0 obj vs 0 R.

The structure of this data, in python/dict form, is thus:

third_obj = {
  '/Type': '/Page'),
  '/Parent': iobj_ref(1),
  '/Resources': iobj_ref(2),
  '/Contents': iobj_ref(4),
}

Content streams are of the form:

4 0 obj
<</Filter /ASCIIHexDecode /Length 22>>
stream
68656c6c6f20776f726c64
endstream
endobj

The contents of this module are internal to fpdf2, and not part of the public API. They may change at any time without prior warning or any deprecation period, in non-backward-compatible ways.

Functions

def build_obj_dict(key_values): Build the PDF Object associative map to serialize, based on a key-values dict. The property names are converted from snake_case to CamelCase, and prefixed with a slash character "/".
def camel_case(snake_case)
def clear_empty_fields(d)
def create_dictionary_string(dict_, open_dict='<<', close_dict='>>', field_join='\n', key_value_join=' ', has_empty_fields=False): format dictionary as PDF dictionary

@param dict_: dictionary of values to render @param open_dict: string to open PDF dictionary @param close_dict: string to close PDF dictionary @param field_join: string to join fields with @param key_value_join: string to join key to value with @param has_empty_fields: whether or not to clear_empty_fields first.
def create_list_string(list_): format list of strings as PDF array
def create_stream(stream, encryption_handler=None, obj_id=None)
def iobj_ref(n): format an indirect PDF Object reference from its id number

Classes

class Destination

Helper class that provides a standard way to create an ABC using inheritance.

Expand source code Browse git

class Destination(ABC):
    def serialize(self, _security_handler=None, _obj_id=None):
        raise NotImplementedError

Ancestors

abc.ABC

Subclasses

DestinationXYZ

Methods

def serialize(self)

class DestinationXYZ (page, top, left=0, zoom='null')

Helper class that provides a standard way to create an ABC using inheritance.

Expand source code Browse git

class DestinationXYZ(Destination):
    def __init__(self, page, top, left=0, zoom="null"):
        self.page_number = page
        self.top = top
        self.left = left
        self.zoom = zoom
        self.page_ref = None

    def __eq__(self, dest):
        return (
            self.page_number == dest.page_number
            and self.top == dest.top
            and self.left == dest.left
            and self.zoom == dest.zoom
        )

    def __hash__(self):
        return hash((self.page_number, self.top, self.left, self.zoom))

    def __repr__(self):
        return f'DestinationXYZ(page_number={self.page_number}, top={self.top}, left={self.left}, zoom="{self.zoom}", page_ref={self.page_ref})'

    def serialize(self, _security_handler=None, _obj_id=None):
        left = round(self.left, 2) if isinstance(self.left, float) else self.left
        top = round(self.top, 2) if isinstance(self.top, float) else self.top
        assert self.page_ref
        return f"[{self.page_ref} /XYZ {left} {top} {self.zoom}]"

Ancestors

Destination
abc.ABC

Methods

def serialize(self)

class Name (...)

str subclass signifying a PDF name, which are emitted differently than normal strings.

Expand source code Browse git

class Name(str):
    """str subclass signifying a PDF name, which are emitted differently than normal strings."""

    NAME_ESC = re.compile(
        b"[^" + bytes(v for v in range(33, 127) if v not in b"()<>[]{}/%#\\") + b"]"
    )

    def serialize(self, _security_handler=None, _obj_id=None) -> str:
        escaped = self.NAME_ESC.sub(
            lambda m: b"#%02X" % m[0][0], self.encode()
        ).decode()
        return f"/{escaped}"

Ancestors

builtins.str

Class variables

var NAME_ESC

Methods

def serialize(self) ‑> str

class PDFArray (*args, **kwargs)

Built-in mutable sequence.

If no argument is given, the constructor creates a new empty list. The argument must be an iterable if specified.

Expand source code Browse git

class PDFArray(list):
    def serialize(self, _security_handler=None, _obj_id=None):
        if all(isinstance(elem, str) for elem in self):
            serialized_elems = " ".join(self)
        elif all(isinstance(elem, int) for elem in self):
            serialized_elems = " ".join(str(elem) for elem in self)
        else:
            serialized_elems = "\n".join(
                (
                    elem.ref
                    if isinstance(elem, PDFObject)
                    else elem.serialize(
                        _security_handler=_security_handler, _obj_id=_obj_id
                    )
                )
                for elem in self
            )
        return f"[{serialized_elems}]"

Ancestors

builtins.list

Methods

def serialize(self)

class PDFContentStream (contents, compress=False)

Main features of this class: * delay ID assignement * implement serializing

Expand source code Browse git

class PDFContentStream(PDFObject):
    # Passed to zlib.compress() - In range 0-9 - Default is currently equivalent to 6:
    _COMPRESSION_LEVEL = -1

    def __init__(self, contents, compress=False):
        super().__init__()
        self._contents = (
            zlib.compress(contents, level=self._COMPRESSION_LEVEL)
            if compress
            else contents
        )
        self.filter = Name("FlateDecode") if compress else None
        self.length = len(self._contents)

    # method override
    def content_stream(self):
        return self._contents

    # method override
    def serialize(self, obj_dict=None, _security_handler=None):
        if _security_handler:
            assert not obj_dict
            if not isinstance(self._contents, (bytearray, bytes)):
                self._contents = self._contents.encode("latin-1")
            self._contents = _security_handler.encrypt(self._contents, self.id)
            self.length = len(self._contents)
        return super().serialize(obj_dict, _security_handler)

Ancestors

PDFObject

Subclasses

Inherited members

PDFObject:
- content_stream
- serialize

class PDFDate (date: datetime.datetime, with_tz=False, encrypt=False)

Args

date : datetime: self-explanatory
with_tz : bool: should the timezone be encoded in included in the date?
encrypt : bool: if document encryption is enabled, should this string be encrypted?

Expand source code Browse git

class PDFDate:
    def __init__(self, date: datetime, with_tz=False, encrypt=False):
        """
        Args:
            date (datetime): self-explanatory
            with_tz (bool): should the timezone be encoded in included in the date?
            encrypt (bool): if document encryption is enabled, should this string be encrypted?
        """
        self.date = date
        self.with_tz = with_tz
        self.encrypt = encrypt

    def __repr__(self):
        return f"PDFDate({self.date}, with_tz={self.with_tz}, encrypt={self.encrypt})"

    def serialize(self, _security_handler=None, _obj_id=None):
        if self.with_tz:
            assert self.date.tzinfo
            if self.date.tzinfo == timezone.utc:
                out_str = f"D:{self.date:%Y%m%d%H%M%SZ}"
            else:
                out_str = f"D:{self.date:%Y%m%d%H%M%S%z}"
                out_str = out_str[:-2] + "'" + out_str[-2:] + "'"
        else:
            out_str = f"D:{self.date:%Y%m%d%H%M%S}"
        if _security_handler and self.encrypt:
            assert _obj_id
            return _security_handler.encrypt_string(out_str, _obj_id)
        return f"({out_str})"

Methods

def serialize(self)

class PDFObject

Main features of this class: * delay ID assignement * implement serializing

Expand source code Browse git

class PDFObject:
    """
    Main features of this class:
    * delay ID assignement
    * implement serializing
    """

    # Note: several child classes use __slots__ to save up some memory

    def __init__(self):
        self._id = None

    @property
    def id(self):
        if self._id is None:
            raise AttributeError(
                f"{self.__class__.__name__} has not been assigned an ID yet"
            )
        return self._id

    @id.setter
    def id(self, n):
        self._id = n

    @property
    def ref(self):
        return iobj_ref(self.id)

    def serialize(self, obj_dict=None, _security_handler=None):
        "Serialize the PDF object as an obj<</>>endobj text block"
        output = []
        output.append(f"{self.id} 0 obj")
        output.append("<<")
        if not obj_dict:
            obj_dict = self._build_obj_dict(_security_handler)
        output.append(create_dictionary_string(obj_dict, open_dict="", close_dict=""))
        output.append(">>")
        content_stream = self.content_stream()
        if content_stream:
            output.append(create_stream(content_stream))
        output.append("endobj")
        return "\n".join(output)

    # pylint: disable=no-self-use
    def content_stream(self):
        "Subclasses can override this method to indicate the presence of a content stream"
        return b""

    def _build_obj_dict(self, security_handler=None):
        """
        Build the PDF Object associative map to serialize,
        based on this class instance properties.
        The property names are converted from snake_case to CamelCase,
        and prefixed with a slash character "/".
        """
        return build_obj_dict(
            {key: getattr(self, key) for key in dir(self)},
            _security_handler=security_handler,
            _obj_id=self.id,
        )

Subclasses

Instance variables

prop id

Expand source code

@property
def id(self):
    if self._id is None:
        raise AttributeError(
            f"{self.__class__.__name__} has not been assigned an ID yet"
        )
    return self._id

prop ref

Expand source code

@property
def ref(self):
    return iobj_ref(self.id)

Methods

def content_stream(self): Subclasses can override this method to indicate the presence of a content stream
def serialize(self, obj_dict=None): Serialize the PDF object as an obj<>endobj text block

class PDFString (content, encrypt=False)

str(object='') -> str str(bytes_or_buffer[, encoding[, errors]]) -> str

Create a new string object from the given object. If encoding or errors is specified, then the object must expose a data buffer that will be decoded using the given encoding and error handler. Otherwise, returns the result of object.str() (if defined) or repr(object). encoding defaults to sys.getdefaultencoding(). errors defaults to 'strict'.

Expand source code Browse git

class PDFString(str):
    USE_HEX_ENCODING = True
    """
    Setting this to False can reduce the encoded strings size,
    but then there can be a risk of badly encoding some unicode strings - cf. issue #458
    """

    def __new__(cls, content, encrypt=False):
        """
        Args:
            content (str): text
            encrypt (bool): if document encryption is enabled, should this string be encrypted?
        """
        self = super().__new__(cls, content)
        self.encrypt = encrypt
        return self

    def serialize(self, _security_handler=None, _obj_id=None):
        if _security_handler and self.encrypt:
            assert _obj_id
            return _security_handler.encrypt_string(self, _obj_id)
        try:
            self.encode("ascii")
            # => this string only contains ASCII characters, no need for special encoding:
            return f"({self})"
        except UnicodeEncodeError:
            pass
        if self.USE_HEX_ENCODING:
            # Using the "Hexadecimal String" format defined in the PDF spec:
            hex_str = hexlify(BOM_UTF16_BE + self.encode("utf-16-be")).decode("latin-1")
            return f"<{hex_str}>"
        return f'({self.encode("UTF-16").decode("latin-1")})'

Ancestors

builtins.str

Class variables

var USE_HEX_ENCODING: Setting this to False can reduce the encoded strings size, but then there can be a risk of badly encoding some unicode strings - cf. issue #458

Methods

def serialize(self)

class Raw (...)

str subclass signifying raw data to be directly emitted to PDF without transformation.

Expand source code Browse git

class Raw(str):
    """str subclass signifying raw data to be directly emitted to PDF without transformation."""

Ancestors

builtins.str