Modified shapeshifter function

python/damask/util.py

@@ -478,33 +478,26 @@ def shapeshifter(fro: _Tuple[int, ...],
     >>> (a * np.broadcast_to(b_extended,a.shape)).shape
     (3,4,2)
 
-
     """
-    if len(fro) == 0 and len(to) == 0: return ()
-
-    beg = dict(left ='(^.*\\b)',
-               right='(^.*?\\b)')
-    sep = dict(left ='(.*\\b)',
-               right='(.*?\\b)')
-    end = dict(left ='(.*?$)',
-               right='(.*$)')
-    fro = (1,) if len(fro) == 0 else fro
-    to  = (1,) if len(to) == 0 else to
-    try:
-        match = _re.match(beg[mode]
-                      +f',{sep[mode]}'.join(map(lambda x: f'{x}'
-                                                          if x>1 or (keep_ones and len(fro)>1) else
-                                                          '\\d+',fro))
-                      +f',{end[mode]}',','.join(map(str,to))+',')
-        assert match
-        grp = match.groups()
-    except AssertionError:
-        raise ValueError(f'shapes cannot be shifted {fro} --> {to}')
-    fill: _Any = ()
-    for g,d in zip(grp,fro+(None,)):
-        fill += (1,)*g.count(',')+(d,)
-    return fill[:-1]
+    if len(fro) == 0 and len(to) == 0: return tuple()
+    _fro = [1] if len(fro) == 0 else list(fro)[::-1 if mode=='left' else 1]
+    _to  = [1] if len(to)  == 0 else list(to) [::-1 if mode=='left' else 1]
 
+    final_shape: _List[int] = []
+    index = 0
+    for i,item in enumerate(_to):
+        if item==_fro[index]:
+            final_shape.append(item)
+            index+=1
+        else:
+            final_shape.append(1)
+            if _fro[index]==1 and not keep_ones:
+                index+=1
+        if index==len(_fro):
+            final_shape = final_shape+[1]*(len(_to)-i-1)
+            break
+    if index!=len(_fro): raise ValueError(f'shapes cannot be shifted {fro} --> {to}')
+    return tuple(final_shape[::-1] if mode=='left' else final_shape)
 
 def shapeblender(a: _Tuple[int, ...],
                  b: _Tuple[int, ...]) -> _Tuple[int, ...]: