From 9a0664f6c2fd1d3376c027eaf87592242c806e12 Mon Sep 17 00:00:00 2001
From: Pavel 'LEdoian' Turinsky <ledoian@matfyz.cz>
Date: Wed, 11 Mar 2020 23:07:58 +0100
Subject: [PATCH] =?UTF-8?q?TreeLib:=20Bezpe=C4=8Dn=C3=A9=20varianty=20.pre?=
 =?UTF-8?q?d=20a=20.father=5Fof=5Ffirst?=
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---
 seminar/treelib.py | 29 ++++++++++++++++-------------
 1 file changed, 16 insertions(+), 13 deletions(-)

diff --git a/seminar/treelib.py b/seminar/treelib.py
index ce956219..b2b106b2 100644
--- a/seminar/treelib.py
+++ b/seminar/treelib.py
@@ -10,23 +10,26 @@ def print_tree(node,indent=0):
 	if node.succ:
 		print_tree(node.succ, indent=indent)
 
+# Django je trošku hloupé, takže node.prev nevrací None, ale hází django.core.exceptions.ObjectDoesNotExist
+def safe_pred(node):
+	try:
+		return node.prev
+	except ObjectDoesNotExist:
+		return None
+
+# A to samé pro .father_of_first
+def safe_father_of_first(node):
+		return node.prev
+	except ObjectDoesNotExist:
+		return None
+
 ## Rodinné vztahy
 def get_parent(node):
-	pass
 	# Nejdřív získáme prvního potomka...
-	# Django je trošku hloupé, takže node.prev nevrací None, ale hází django.core.exceptions.ObjectDoesNotExist
-	while True:
-		try:
-			node = node.prev
-		except ObjectDoesNotExist:
-			# We rely here on the fact that the assignment will not happen if RHS throws an exception
-			break
+	while safe_pred(node) is not None:
+		node = safe_pred(node)
 	# ... a z prvního potomka umíme najít rodiče
-	# Django je pořád hloupé...
-	try:
-		return node.father_of_first
-	except ObjectDoesNotExist:
-		return None
+	return safe_father_of_first(node)
 
 # Obecný next: další Node v "the-right-order" pořadí (já, pak potomci, pak sousedé)
 def general_next(node):