PyPreviewGenerator 0.1.19

Generation of file previews

Presentation

This module allows to generate jpeg, pdf, text or html preview for virtually any kind of files including a cache management. It allows to generate preview for a given page and put it in cache. The context of creation of this module (as an example of use context) was for Tracim, a github project (https://github.com/Tracim/tracim) where users can put file on a repository in order to share it with other users. The only way to find a file was with his name. Hence it was decided to generate previews of the files in order to ease the location of one. Only works on Linux.

It is distributed with MIT license (https://choosealicense.com/licenses/mit/)

Format handled

	JPEG	PDF	TEXT	HTML	JSON
PNG	☑				☑
JPEG	☑				☑
BMP	☑				☑
GIF	☑				☑
PDF	☑
Compressed files			☑	☑	☑
Office files (word, LibreOffice)	☑	☑
Text			☑

Installation

pip install PyPreviewGenerator

Requirement

Some packages are needed but may also be already on your OS. You can check if they are already installed or you can just try to install PyPreviewGenerator and if the pip install PyPreviewGenerator command fails, do :

apt-get install zlib1g-dev

apt-get install libjpeg-dev

and try pip install PyPreviewGenerator again.

This package uses several libraries :

• wand

• python-magick

• pillow

• PyPDF2

These should be automatically installed with the pip install PyPreviewGenerator command. But if some error occurs quoting one of these library, try to install them 1 by 1 with a simple pip install … to locate the library that causes the problem.

WARNING! about LibreOffice

If you want to use the conversion from an office file to pdf or jpeg, ensure that LibreOffice is already installed on the computer because the conversion is made by the Libreoffice’s export feature.

LibreOffice’s download page : https://fr.libreoffice.org/download/libreoffice-stable/

Usage

Getting a preview

from PyPreviewGenerator.manager import PreviewManager
manager = PreviewManager(path='/home/user/Pictures/')
path_to_file = manager.get_jpeg_preview(
  file_path='/home/user/Pictures/myfile.gif',
  height=100,
  width=100,
)
print('Preview created at path : ', path_to_file)

The preview manager

preview_manager = PreviewManager(cache_path)

args :

cache_path : a String of the path to the directory where the cache file will be stored

returns :

a PreviewManager Object

The builders

Here is the way it is meant to be used

For Office types into PDF :

preview_manager = PreviewManager(cache_path)
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 page you want to get. If not mentioned all the pages will be returned. First page is page 0

returns :

a FileIO stream of bytes of the pdf preview

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

preview_manager = PreviewManager(cache_path)
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 :

a FileIO stream of bytes of the jpeg preview

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

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 PyPreviewGenerator.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_gif.gif',
    height=512,
    width=512,
)

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

will print

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

ODT to JPEG :

import os
from PyPreviewGenerator.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_file)

will print

Preview created at path : the_odt-1024x1024-c8b37debbc45fa96466e5e1382f6bd2e(1).jpeg

ZIP to Text :

import os
from PyPreviewGenerator.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) 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 PyPreviewGenerator/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 you 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 PyPreviewGenerator.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