Whitelist +, #, ., - and – special characters

Author: mjenczmyk

setup.py

@@ -10,7 +10,7 @@
     'click==7.0',
     'google-api-python-client==1.6.3',
     'requests==2.20.0',
-    'python-slugify==1.2.6'
+    'python-slugify==4.0.0'
 ]
 
 dev_requirements = [

src/downloader.py

@@ -1,4 +1,5 @@
 import os
+import re
 import sys
 import time
 
@@ -23,7 +24,13 @@ class PacktConnectionError(ConnectionError):
 
 def slugify_product_name(title):
     """Return book title with spaces replaced by underscore and unicodes replaced by characters valid in filenames."""
-    return slugify(title, separator='_', lowercase=False)
+    return slugify(
+        title,
+        separator='_',
+        lowercase=False,
+        regex_pattern=re.compile(r'[^-a-zA-Z0-9\+\#\.\-\–]+'),
+        replacements=[['–', '-']]
+    )
 
 
 def wait_for_computation(predicate, timeout, retry_after):