Module `fpdf.syntax`

PDF Syntax Helpers

Functions in this module take variable input and produce PDF Syntax features.

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

In this case, the ASCIIHexDecode filter is used because "68656c6c6f20776f726c64" is "hello world" in ascii, and 22 is the length of that string.

Expand source code

"""**PDF Syntax Helpers**

Functions in this module take variable input and produce PDF Syntax features.

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
```

In this case, the ASCIIHexDecode filter is used because
"68656c6c6f20776f726c64" is "hello world" in ascii, and 22 is the length of that string.
"""
import re, zlib
from abc import ABC
from binascii import hexlify
from codecs import BOM_UTF16_BE


def clear_empty_fields(d):
    return {k: v for k, v in d.items() if v}


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.
    """
    if has_empty_fields:
        dict_ = clear_empty_fields(dict_)

    return "".join(
        [
            open_dict,
            field_join.join(key_value_join.join((k, str(v))) for k, v in dict_.items()),
            close_dict,
        ]
    )


def create_list_string(list_):
    """format list of strings as PDF array"""
    return f"[{' '.join(list_)}]"


def iobj_ref(n):
    """format an indirect PDF Object reference from its id number"""
    return f"{n} 0 R"


def create_stream(stream, encryption_handler=None, obj_id=None):
    if isinstance(stream, (bytearray, bytes)):
        stream = str(stream, "latin-1")
    if encryption_handler:
        encryption_handler.encrypt(stream, obj_id)
    return "\n".join(["stream", stream, "endstream"])


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


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}"


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

    # pylint: disable=redefined-builtin
    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)
        elif _security_handler:
            obj_dict = self._encrypt_obj_dict(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)

    def content_stream(self):
        "Subclass 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,
        )

    def _encrypt_obj_dict(self, obj_dict, security_handler):
        """Encrypt the strings present in the object dictionary"""
        for key in obj_dict:
            string = obj_dict[key]
            if (
                isinstance(string, str)
                and string.startswith("(")
                and string.endswith(")")
            ):
                obj_dict[key] = security_handler.encrypt(string[1:-1], self.id)
        return obj_dict


class PDFContentStream(PDFObject):
    def __init__(self, contents, compress=False):
        super().__init__()
        self._contents = zlib.compress(contents) 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

    def encrypt(self, security_handler):
        self._contents = security_handler.encrypt(self._contents, self.id)
        self.length = len(self._contents)


def build_obj_dict(key_values, _security_handler=None, _obj_id=None):
    """
    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 "/".
    """
    obj_dict = {}
    for key, value in key_values.items():
        if (
            callable(value)
            or key.startswith("_")
            or key in ("id", "ref")
            or value is None
        ):
            continue
        if hasattr(value, "value"):  # e.g. Enum subclass
            value = value.value
        if isinstance(value, PDFObject):  # indirect object reference
            value = value.ref
        elif hasattr(value, "serialize"):
            # e.g. PDFArray, PDFString, Name, Destination, Action...
            value = value.serialize(
                _security_handler=_security_handler, _obj_id=_obj_id
            )
        elif isinstance(value, bool):
            value = str(value).lower()
        if (
            _security_handler
            and isinstance(value, str)
            and value.startswith("(")
            and value.endswith(")")
        ):
            value = _security_handler.encrypt(value[1:-1], _obj_id)
        obj_dict[f"/{camel_case(key)}"] = value
    return obj_dict


def camel_case(snake_case):
    return "".join(x for x in snake_case.title() if x != "_")


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 serialize(self, _security_handler=None, _obj_id=None):
        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")})'


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(map(str, 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}]"


# cf. section 8.2.1 "Destinations" of the 2006 PDF spec 1.7:
class Destination(ABC):
    def serialize(self, _security_handler=None, _obj_id=None):
        raise NotImplementedError


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 __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}]"

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 "/".

Expand source code

def build_obj_dict(key_values, _security_handler=None, _obj_id=None):
    """
    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 "/".
    """
    obj_dict = {}
    for key, value in key_values.items():
        if (
            callable(value)
            or key.startswith("_")
            or key in ("id", "ref")
            or value is None
        ):
            continue
        if hasattr(value, "value"):  # e.g. Enum subclass
            value = value.value
        if isinstance(value, PDFObject):  # indirect object reference
            value = value.ref
        elif hasattr(value, "serialize"):
            # e.g. PDFArray, PDFString, Name, Destination, Action...
            value = value.serialize(
                _security_handler=_security_handler, _obj_id=_obj_id
            )
        elif isinstance(value, bool):
            value = str(value).lower()
        if (
            _security_handler
            and isinstance(value, str)
            and value.startswith("(")
            and value.endswith(")")
        ):
            value = _security_handler.encrypt(value[1:-1], _obj_id)
        obj_dict[f"/{camel_case(key)}"] = value
    return obj_dict

def camel_case(snake_case)

Expand source code

def camel_case(snake_case):
    return "".join(x for x in snake_case.title() if x != "_")

def clear_empty_fields(d)

Expand source code

def clear_empty_fields(d):
    return {k: v for k, v in d.items() if v}

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.

Expand source code

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.
    """
    if has_empty_fields:
        dict_ = clear_empty_fields(dict_)

    return "".join(
        [
            open_dict,
            field_join.join(key_value_join.join((k, str(v))) for k, v in dict_.items()),
            close_dict,
        ]
    )

def create_list_string(list_)

format list of strings as PDF array

Expand source code

def create_list_string(list_):
    """format list of strings as PDF array"""
    return f"[{' '.join(list_)}]"

def create_stream(stream, encryption_handler=None, obj_id=None)

Expand source code

def create_stream(stream, encryption_handler=None, obj_id=None):
    if isinstance(stream, (bytearray, bytes)):
        stream = str(stream, "latin-1")
    if encryption_handler:
        encryption_handler.encrypt(stream, obj_id)
    return "\n".join(["stream", stream, "endstream"])

def iobj_ref(n)

format an indirect PDF Object reference from its id number

Expand source code

def iobj_ref(n):
    """format an indirect PDF Object reference from its id number"""
    return f"{n} 0 R"

Classes

class Destination

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

Expand source code

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

Ancestors

abc.ABC

Subclasses

DestinationXYZ

Methods

def serialize(self)

Expand source code

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

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

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

Expand source code

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 __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)

Expand source code

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}]"

class Name (...)

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

Expand source code

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

Expand source code

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}"

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

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(map(str, 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)

Expand source code

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(map(str, 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}]"

class PDFContentStream (contents, compress=False)

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

Expand source code

class PDFContentStream(PDFObject):
    def __init__(self, contents, compress=False):
        super().__init__()
        self._contents = zlib.compress(contents) 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

    def encrypt(self, security_handler):
        self._contents = security_handler.encrypt(self._contents, self.id)
        self.length = len(self._contents)

Ancestors

PDFObject

Subclasses

Methods

def encrypt(self, security_handler)

Expand source code

def encrypt(self, security_handler):
    self._contents = security_handler.encrypt(self._contents, self.id)
    self.length = len(self._contents)

Inherited members

PDFObject:
- content_stream
- serialize

class PDFObject

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

Expand source code

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

    # pylint: disable=redefined-builtin
    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)
        elif _security_handler:
            obj_dict = self._encrypt_obj_dict(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)

    def content_stream(self):
        "Subclass 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,
        )

    def _encrypt_obj_dict(self, obj_dict, security_handler):
        """Encrypt the strings present in the object dictionary"""
        for key in obj_dict:
            string = obj_dict[key]
            if (
                isinstance(string, str)
                and string.startswith("(")
                and string.endswith(")")
            ):
                obj_dict[key] = security_handler.encrypt(string[1:-1], self.id)
        return obj_dict

Subclasses

Instance variables

var 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

var ref

Expand source code

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

Methods

def content_stream(self)

Subclass can override this method to indicate the presence of a content stream

Expand source code

def content_stream(self):
    "Subclass can override this method to indicate the presence of a content stream"
    return b""

def serialize(self, obj_dict=None)

Serialize the PDF object as an obj<>endobj text block

Expand source code

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)
    elif _security_handler:
        obj_dict = self._encrypt_obj_dict(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)

class PDFString (...)

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

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 serialize(self, _security_handler=None, _obj_id=None):
        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)

Expand source code

def serialize(self, _security_handler=None, _obj_id=None):
    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")})'

class Raw (...)

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

Expand source code

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

Ancestors

builtins.str