Removing join function and using filter instead

q2/main.py

@@ -12,3 +12,23 @@ print(l)
 L = [["this"],["is"],["the"],["easiest"],["problem"],["of"],["this"],["outlab"]]
 l=collapse(L)
 print(l) 
+
+L = [["this"]]
+l=collapse(L)
+print(l)
+
+L = [[], ["Once", "upon", "a", "time"], ["in", "a", "galaxy", "far", "far", "away"]]
+l=collapse(L)
+print(l)
+
+L = [[str(2), "+", str(2)], ['='], [str(5)]]
+l=collapse(L)
+print(l)
+
+L = [[],[],[],[],[],[]]
+l=collapse(L)
+print(l)
+
+L = [[str(2), "+", str(2)], ['='], [str(5)]]
+l=collapse(L)
+print(l)
\ No newline at end of file

q2/output

 this is an interesting python programming exercise.
 this is a bad problem
 this is the easiest problem of this outlab
+this
+Once upon a time in a galaxy far far away
+2 + 2 = 5
+
+2 + 2 = 5
\ No newline at end of file

q2/q2.py

 import functools
-import operator
 
 def collapse(L) :
-    flat = functools.reduce(lambda x,y: operator.concat(x,y), L)
-    return " ".join(flat)
+    flat = functools.reduce(lambda x,y: x+y, L)
+    if flat:
+        return functools.reduce(lambda x,y: x + " " + y, flat)
+    else:
+        return ""