GeezerVison

API

This article introduces the principles.

Quick access to specific articles:

• High-level API
• Low-level API

Pure functions

Most functions are pure and are exposed both as basic functions and as instance methods of a Doc object: in the function signatures found in the following sections, a doc first argument can read as self. For example both samples are equivalent:

>>> #Function pattern
>>> from pdfsyntax import readfile, metadata
>>> doc = readfile("samples/simple_text_string.pdf")
>>> m = metadata(doc)

>>> #Method pattern
>>> import pdfsyntax as pdf
>>> doc = pdf.readfile("samples/simple_text_string.pdf")
>>> m = doc.metadata()

Every time a function is applied to a Doc object, the function returns a new object built as a shallow copy of the input.

Incremental updates

PDFSyntax tracks document incremental updates made possible by appending new or updated objects at the end of an original PDF file (and the matching XREF section). A revision, if greater than 0, indicates that incremental updates have been appended.By default, a newly opened document by PDFSyntax is ready to write modifications in the next revision.The rewind function rolls back to the previous revision. The commit function closes the current revision and open the next one.

For example this file contains 2 revisions (0 and 1) and PDFSyntax has initialized the doc object to open revision 2:

>>> import pdfsyntax as pdf
>>> doc = pdf.readfile("samples/add_text_annotation.pdf")
>>> doc
<PDF Doc in revision 2 with 0 modified object(s)>

The rewind function rolls back to the previous revision. Let's rewind to revision 0:

>>> doc = pdf.rewind(doc) # to revision 1
>>> doc = pdf.rewind(doc) # to revision 0
>>> doc
<PDF Doc in revision 0 with 7 modified object(s)>

After one or several modifications, the commit function closes the current revision and opens the next one:

>>> doc = pdf.rotate(doc)
>>> doc = pdf.commit(doc)
>>> doc
<PDF Doc in revision 1 with 0 modified object(s)>

Squashing

By default incremental updates stack up but it is possible to squash a document in order to combine all revisions into a single one. in this example the last document is equivalent to the first one (same appearance), but it is only made of one revision. As this revision is like a document started from scratch, its revision is 0 and all its 7 internal objects look like new ones:

>>> doc90 = pdf.rotate(doc)
>>> doc90
<PDF Doc in revision 1 with 1 modified object(s)>
>>> docs = pdf.squash(doc90)
>>> docs
<PDF Doc in revision 0 with 7 modified object(s)>

File I/O

The writefile function dumps the document with all the incremental updates appended at the end of the original data.

>>> from pdfsyntax import readfile, writefile
>>> doc = readfile("samples/simple_text_string.pdf")
>>> doc90 = pdf.rotate(doc)
>>> writefile(doc90, "rotated_doc.pdf")

TO BE CONTINUED