Restore PDFTextExtractionNotAllowed exception (#461)

* Restore PDFTextExtractionNotAllowed 

Restore PDFTextExtractionNotAllowed  exception class as an alias of the
new PDFTextExtractionNotAllowedError exception that was introduced in
6a9269b

Removing PDFTextExtractionNotAllowed is an API breakage that made
several tools fail break.

Signed-off-by: Philippe Ombredanne <pombredanne@nexb.com>

* Use PDFTextExtractionNotAllowed and prepare PDFTextExtractionNotAllowedError to be removed in the future

* Add line to CHANGELOG.md

Co-authored-by: Pieter Marsman <pietermarsman@gmail.com>

CHANGELOG.md

@@ -3,12 +3,17 @@ All notable changes in pdfminer.six will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
+## [20200726]
+
+### Fixed
+- Rename PDFTextExtractionNotAllowedError to PDFTextExtractionNotAllowed to revert breaking change ([#461](https://github.com/pdfminer/pdfminer.six/pull/461))
+
 ## [20200720]
 
 ### Added
 - Support for painting multiple rectangles at once ([#371](https://github.com/pdfminer/pdfminer.six/pull/371))
 
-## Fixed
+### Fixed
 - Always try to get CMap, not only for identity encodings ([#438](https://github.com/pdfminer/pdfminer.six/pull/438))
 - Validate image object in do_EI is a PDFStream ([#451](https://github.com/pdfminer/pdfminer.six/pull/451))
 

pdfminer/pdfdocument.py

@@ -46,10 +46,18 @@ class PDFTextExtractionNotAllowedWarning(UserWarning):
     pass
 
 
-class PDFTextExtractionNotAllowedError(PDFEncryptionError):
+class PDFTextExtractionNotAllowed(PDFEncryptionError):
     pass
 
 
+class PDFTextExtractionNotAllowedError(PDFTextExtractionNotAllowed):
+    def __init__(self, *args):
+        from warnings import warn
+        warn('PDFTextExtractionNotAllowedError will be removed in the future. '
+             'Use PDFTextExtractionNotAllowed instead.', DeprecationWarning)
+        super().__init__(*args)
+
+
 # some predefined literals and keywords.
 LITERAL_OBJSTM = LIT('ObjStm')
 LITERAL_XREF = LIT('XRef')