Use absolute import to work around circular builder/tesseract import …

…issues.

Unfortunately builders.py now imports psm_parameter from tesseract.py,
and tesseract.py imports DigitBuilder from builders.py. We could move
psm_parameter into util.py, but it needs get_version as well and it is
very much tesseract specific. I do not see a great solution for this and
keeping the circular import seems the least bad solution. We keep it
from breaking the program by using an explicit import of the module [0].

[0] https://stackoverflow.com/a/37126790

src/pyocr/builders.py

@@ -14,7 +14,7 @@
 import xml.dom.minidom
 import logging
 
-from .tesseract import psm_parameter
+import pyocr.tesseract
 from .util import to_unicode
 
 logger = logging.getLogger(__name__)
@@ -306,7 +306,7 @@ class TextBuilder(BaseBuilder):
     def __init__(self, tesseract_layout=3, cuneiform_dotmatrix=False,
                  cuneiform_fax=False, cuneiform_singlecolumn=False):
         file_ext = ["txt"]
-        tess_flags = [psm_parameter(), str(tesseract_layout)]
+        tess_flags = [pyocr.tesseract.psm_parameter(), str(tesseract_layout)]
         cun_args = ["-f", "text"]
         # Add custom cuneiform parameters if needed
         for par, arg in [(cuneiform_dotmatrix, "--dotmatrix"),
@@ -563,7 +563,7 @@ class WordBoxBuilder(BaseBuilder):
 
     def __init__(self, tesseract_layout=1):
         file_ext = ["html", "hocr"]
-        tess_flags = [psm_parameter(), str(tesseract_layout)]
+        tess_flags = [pyocr.tesseract.psm_parameter(), str(tesseract_layout)]
         tess_conf = ["hocr"]
         cun_args = ["-f", "hocr"]
         super(WordBoxBuilder, self).__init__(file_ext, tess_flags, tess_conf,
@@ -639,7 +639,7 @@ class LineBoxBuilder(BaseBuilder):
 
     def __init__(self, tesseract_layout=1):
         file_ext = ["html", "hocr"]
-        tess_flags = [psm_parameter(), str(tesseract_layout)]
+        tess_flags = [pyocr.tesseract.psm_parameter(), str(tesseract_layout)]
         tess_conf = ["hocr"]
         cun_args = ["-f", "hocr"]
         super(LineBoxBuilder, self).__init__(file_ext, tess_flags, tess_conf,