seperate function "pretty_c14n" unsed in program "pretty_c14n.py"

pretty_c14n.py

+#!/usr/bin/env python3
+
+import sys
+from trans import pretty_c14n
+
+def error_and_exit(x):
+    print('ERROR: ', str(x), file=sys.stderr)
+    sys.exit(1)
+    
+if len(sys.argv) < 3:
+    error_and_exit('too few arguments')
+if sys.argv[1] == sys.argv[2]:
+    error_and_exit('"infile" and "outfile" must be different')
+
+infile = sys.argv[1]
+outfile = sys.argv[2]
+
+try:
+    with open(infile, 'r') as f1:
+        xml = f1.read()
+        with open(outfile, 'w') as f2: 
+            err, xml = pretty_c14n(xml)
+            if err:
+                error_and_exit(xml)
+            f2.write(xml)
+except Exception as error:
+    error_and_exit(error)
+    
+print('\nFile »' +  infile + '« was successfully canonized to file »' + \
+  outfile + '«\n')
+
+sys.exit(0)

trans.py

@@ -9,6 +9,20 @@ config = utils.config
 
 from pprint import pprint
 
+def pretty_c14n(_xml):
+    xml = _xml
+    err = False
+    try: 
+        xml = etree.canonicalize(xml, with_comments=True, strip_text=True)
+        # Bad side-effect of "prettify_xml": adds XML declaration again
+        xml = prettify_xml(xml, indent=2, debug=False)
+        xml = etree.canonicalize(xml, with_comments=True)
+    except Exception as error:
+        xml = str(error)
+        err = True
+        
+    return err, xml
+
 def cert_to_xml(cert_doc): 
     dcc_template = config['main_xml_template']
     ###pprint(config)
@@ -22,12 +36,12 @@ def cert_to_xml(cert_doc):
     cert_doc['DCC']['administrativeData']['dccSoftware'].append(s)
     try: 
         xml = render_template(dcc_template, doc=cert_doc['DCC'], utils=utils)
-        xml = etree.canonicalize(xml, with_comments=True, strip_text=True)
-        # Bad side-effect: adds XML declaration again
-        xml = prettify_xml(xml, indent=2, debug=False)
-        xml = etree.canonicalize(xml, with_comments=True)
+        err, xml = pretty_c14n(xml)
+        if err:
+            xml = '<error>' + xml + '</error>\n' 
+            
     except Exception as error:
         xml = '<error>' + str(error) + '</error>\n'
-    
+        
     return xml