Initial implementation of OCR pluggable backends

mayan/apps/ocr/backends/__init__.py

@@ -0,0 +1,26 @@
+from __future__ import absolute_import
+
+from django.utils.importlib import import_module
+
+from ..conf.settings import BACKEND
+
+
+class BackendBase(object):
+    def execute(input_filename, language=None):
+        raise NotImplemented
+
+
+def get_ocr_backend():
+    """
+    Return the OCR backend using the path specified in the configuration
+    settings
+    """
+    try:
+        module = import_module(BACKEND)
+    except ImportError:
+        sys.stderr.write(u'\nWarning: No OCR backend named: %s\n\n' % BACKEND)
+        raise
+    else:
+        return module
+
+ocr_backend = get_ocr_backend()

mayan/apps/ocr/backends/tesseract.py

@@ -0,0 +1,45 @@
+from __future__ import absolute_import
+
+import codecs
+import os
+import subprocess
+import tempfile
+import sys
+
+from . import BackendBase
+from ..conf.settings import TESSERACT_PATH
+
+
+def Tesseract(BackendBase):
+    def execute(input_filename, language=None):
+        """
+        Execute the command line binary of tesseract
+        """
+        fd, filepath = tempfile.mkstemp()
+        os.close(fd)
+        ocr_output = os.extsep.join([filepath, u'txt'])
+        command = [unicode(TESSERACT_PATH), unicode(input_filename), unicode(filepath)]
+
+        if lang is not None:
+            command.extend([u'-l', language])
+
+        proc = subprocess.Popen(command, close_fds=True, stderr=subprocess.PIPE, stdout=subprocess.PIPE)
+        return_code = proc.wait()
+        if return_code != 0:
+            error_text = proc.stderr.read()
+            cleanup(filepath)
+            cleanup(ocr_output)
+            if lang:
+                # If tesseract gives an error with a language parameter
+                # re-run it with no parameter again
+                return run_tesseract(input_filename, language=None)
+            else:
+                raise TesseractError(error_text)
+
+        fd = codecs.open(ocr_output, 'r', 'utf-8')
+        text = fd.read().strip()
+        fd.close()
+
+        os.unlink(filepath)
+
+        return text