Preview-generator Documentation

Presentation

preview-generator is a library for generating preview - thumbnails, pdf, text and json overview for all your file-based content. This module gives you access to jpeg, pdf, text, html and json preview of virtually any kind of file. It also includes a cache mechanism so you do not have to care about preview storage.

By creating this module, the goal was to delegate the responsibility of building preview of files managed by tracim.

Supported file formats

Here is an overview of supported file formats:

Installation

Dependencies:

apt-get install zlib1g-dev libjpeg-dev python3-pythonmagick inkscape xvfb poppler-utils libfile-mimeinfo-perl qpdf

At the moment there are issues with the exiftool package on debian, so you'll need to install it manually:

# Exiftool
wget https://sno.phy.queensu.ca/~phil/exiftool/Image-ExifTool-11.11.tar.gz
gzip -dc Image-ExifTool-11.11.tar.gz | tar -xf -
cd Image-ExifTool-11.11
perl Makefile.PL
sudo make install

After installing dependencies, you can install preview-generator using pip:

pip install preview-generator

Optional dependencies:

To handle previews for office documents you will need LibreOffice, if you don't have it already:

apt-get install libreoffice

To check dependencies, you can run:

preview --check-dependencies

Usage

Here are some examples of code

Basic Usage

Most basic usage, create a jpeg from a png, default size 256x256

from preview_generator.manager import PreviewManager

cache_path = '/tmp/preview_cache'
file_to_preview_path = '/tmp/an_image.png'

manager = PreviewManager(cache_path, create_folder= True)
path_to_preview_image = manager.get_jpeg_preview(file_to_preview_path)

Preview an image with a specific size

You can choose the size of your image using params width and height.

from preview_generator.manager import PreviewManager

cache_path = '/tmp/preview_cache'
file_to_preview_path = '/tmp/an_image.png'

manager = PreviewManager(cache_path, create_folder= True)
path_to_preview_image = manager.get_jpeg_preview(file_to_preview_path, width=1000, height=500)

Preview a pdf or an office document as a jpeg

from preview_generator.manager import PreviewManager

cache_path = '/tmp/preview_cache'
pdf_or_odt_to_preview_path = '/tmp/a_pdf.pdf'

manager = PreviewManager(cache_path, create_folder= True)
path_to_preview_image = manager.get_jpeg_preview(pdf_or_odt_to_preview_path)

By default it will generate the preview of the first page of the document. Using params page, you can you pick the page you want to preview.

page number starts at 0, if you want to preview the second page of your document then the argument will be 1 `page=1`

from preview_generator.manager import PreviewManager

cache_path = '/tmp/preview_cache'
pdf_or_odt_to_preview_path = '/tmp/a_pdf.pdf'

manager = PreviewManager(cache_path, create_folder= True)
path_to_preview_image = manager.get_jpeg_preview(pdf_or_odt_to_preview_path, page=1)

Generate a pdf preview of a libreoffice text document

from preview_generator.manager import PreviewManager
manager = PreviewManager('/tmp/cache/', create_folder= True)
pdf_file_path = manager.get_pdf_preview('/home/user/Documents/report.odt', page=2)
print('Preview created at path : ', thumbnail_file_path)

For Office types into PDF :

cache_path = '/tmp/previews'
preview_manager = PreviewManager(cache_path, create_folder= True)
path_to_preview = preview_manager.get_pdf_preview(file_path,page=page_id)

-> Will create a preview from an office file into a pdf file

args :

file_path : the String of the path where is the file you want to get the preview

page : the int of the page you want to get. If not mentioned all the pages will be returned. First page is page 0

returns :

str: path to the preview file

For images(GIF, BMP, PNG, JPEG, PDF) into jpeg :

cache_path = '/tmp/previews'
preview_manager = PreviewManager(cache_path, create_folder= True)
path_to_preview = preview_manager.get_jpeg_preview(file_path,height=1024,width=526)

-> Will create a preview from an image file into a jpeg file of size 1024 * 526

args :

file_path : the String of the path where is the file you want to get the preview

height : height of the preview in pixels

width : width of the preview in pixels. If not mentioned, width will be the same as height

returns :

str: path to the preview file

Other conversions :

The principle is the same as above

Zip to text or html : will build a list of files into texte/html inside the json

Office to jpeg : will build the pdf out of the office file and then build the jpeg.

Text to text : mainly just a copy stored in the cache

Command Line

For test purposes, you can use preview from the command line, giving the file to preview as a parameter:

preview demo.pdf

Or multiple files:

preview *.pdf

Cache mechanism

Naming :

The name of the preview generated in the cache directory will be :

{file_name}-[{size}-]{file_md5sum}[({page})]{extension}

file_name = the name of the file you asked for a preview without the extension.

size = the size you asked for the preview. In case of a Jpeg preview.

file_md5sum = the md5sum of the entire path of the file. To avoid conflicts like files that have the same name but are in different directory.

page = the page asked in case of pdf or office document preview.

extensions = the extension of the preview (.jpeg for a jpeg, .txt for a text, etc)

Example :

These scripts :

GIF to JPEG :

import os
from preview_generator.manager import PreviewManager
current_dir = os.path.dirname(os.path.abspath(__file__)) +'/'

manager = PreviewManager(path=current_dir + 'cache')
path_to_preview = manager.get_jpeg_preview(
    file_path=current_dir + 'the_gif.gif',
    height=512,
    width=512,
)

print('Preview created at path : ', path_to_preview)

will print

Preview created at path : the_gif-512x512-60dc9ef46936cc4fff2fe60bb07d4260.jpeg

ODT to JPEG :

import os
from preview_generator.manager import PreviewManager
current_dir = os.path.dirname(os.path.abspath(__file__)) +'/'

manager = PreviewManager(path=current_dir + 'cache')
path_to_file = manager.get_jpeg_preview(
    file_path=current_dir + 'the_odt.odt',
    page=1,
    height=1024,
    width=1024,
)

print('Preview created at path : ', path_to_preview)

will print

Preview created at path : the_odt-1024x1024-c8b37debbc45fa96466e5e1382f6bd2e-page1.jpeg

ZIP to Text :

import os
from preview_generator.manager import PreviewManager
current_dir = os.path.dirname(os.path.abspath(__file__)) +'/'

manager = PreviewManager(path=current_dir + 'cache')
path_to_file = manager.get_text_preview(
    file_path=current_dir + 'the_zip.zip',
)

print('Preview created at path : ', path_to_file)

will print

Preview created at path : the_zip-a733739af8006558720be26c4dc5569a.txt

Adding new feature :

Before all, I'd be glad if you could share your new feature with everybody. So if you want to, you can fork it on github ( https://github.com/algoo/preview-generator) (see Developer’s Kit) and submit new features.

If you want to add a new preview builder to handle documents of type foo into jpeg (for example) here is how to proceed :

• Warning If you need to look at other builders to find out how to proceed, avoid looking at any of the Office to something. It is a particular case and could misslead you.
• Create a new class FooPreviewBuilder in a file foo_preview.py in preview_generator/preview
• Make him inherit from the logical PreviewBuilder class
  • if it handles several pages it will be class FooPreviewBuilder(PreviewBuilder)
  • for single page it will be class FooPreviewBuilder(OnePagePreviewBuilder)
  • ...
• define your own build_jpeg_preview(...) (in the case we want to make foo into jpeg) based on the same principle as other build_{type}_preview(...)
• Inside this build_jpeg_preview(...) you will call a method file_converter.foo_to_jpeg(...)
• Define your foo_to_jpeg(...) method in preview_generator.preview.file_converter.py
  • inputs must be a stream of bytes and optional informations like a number of pages, a size, ...
  • output must also be a stream of bytes
• Maybe you'll need to redefine some methods like get_page_number() or exists_preview() in your FooPreviewBuilder class

Developer’s Kit

Installation (dev) :

From scratch on a terminal :

• create your project directory (we will name it "the_project" but you can name it the way you want) : mkdir the_project

• cd the_project

• git clone https://github.com/algoo/preview-generator

• building your environment :

  • install python virtualenv builder : sudo apt install python3-venv
  • build your virtual env (env will be called "myenv", you can name it the way you want): python3 -m venv myenv
  • if it's not already, activate it : source myenv/bin/activate. (deactivate to deactivate)

• install dependencies :

  • Exiftool - Follow instruction on the main website: https://sno.phy.queensu.ca/~phil/exiftool/
  • apt-get install zlib1g-dev
  • apt-get install libjpeg-dev
  • apt-get install python3-pythonmagick
  • apt-get install inkscape
  • apt-get install xvfb
  • apt-get install poppler-utils
  • apt-get install qpdf
  • apt-get install libfile-mimeinfo-perl
  • pip install wand
  • pip install Pillow
  • pip install PyPDF2
  • pip install python-magic
  • pip install pyexifinfo
  • pip install packaging
  • pip install xvfbwrapper
  • pip install pdf2image
  • pip install pathlib
  • if you use python 3.5 or less pip install typing

# general dependencies
apt-get install zlib1g-dev libjpeg-dev python3-pythonmagick inkscape xvfb poppler-utils qpdf libfile-mimeinfo-perl
pip install wand Pillow PyPDF2 python-magic pyexifinfo packaging xvfbwrapper pdf2image pathlib
# Exiftool
wget https://sno.phy.queensu.ca/~phil/exiftool/Image-ExifTool-11.11.tar.gz
gzip -dc Image-ExifTool-11.11.tar.gz | tar -xf -
cd Image-ExifTool-11.11
perl Makefile.PL
sudo make install

If you need to preview scribus .sla files you will need scribus >= 1.5. If it's not available in your distribution you can use an AppImage.

Download the last AppImage from the official website https://www.scribus.net/downloads/unstable-branch/

mv /path/to/image/scribus-x.y.appimage /usr/local/bin/scribus
chmod +x /usr/local/bin/scribus

Code Convention :

When using subclass of generic abstract class, convention is to prefix it with name of the generic abstract class. For example:

ImagePreviewBuilderIMConvert(ImagePreviewBuilder)

Running Tests :

Pytest is a motor for unit testing

• pip install -e .[testing]
• go into the "tests" directory : cd path/to/you/project/directory/tests
• run pytest

Others checks :

Run mypy checks:

mypy --ignore-missing-imports --disallow-untyped-defs .

Code formatting using black:

black -l 100 preview_generator setup.py build_supported_mimetypes_table_rst.py tests

Sorting of import:

isort tests/**/*.py preview_generator/**/*.py setup.py build_supported_mimetypes_table_rst.py

Flake8 check(unused import, variable and many other checks):

flake8 preview_generator setup.py build_supported_mimetypes_table_rst.py tests

Contribute :

install preview_generator with dev dependencies (contains tests dependencies)

pip install -e '.[dev]

install pre-commit hooks:

pre-commit install

Launch test :

pytest

You now can commit and see if pre-commit is ok with your change.

License

MIT licensed. https://opensource.org/licenses/MIT