# Compute perfect matchings in a graph

I am trying to calculate all the perfect matchings of a graph G (i. e., the subgraphs of G such that every two points are connected)

```
def matchings(G):
"""Returns a list of the perfect matchings of G.
It uses a recursive algorithm. Get a vertex x in G.
Since all the perfect matchings contain exactly one edge for every vertex,
we have that matchings(G) = {<x,y> U matchings(G\{x,y}) for y adjacent to x}.
"""
Ms=[] #List of mathchings
x = G.random_vertex()
for e in G.edges_incident(x):
H=G.copy()
H.delete_vertices([e[0],e[1]]
for M in matchings(H):
Ms.append(M.add_edge(e))
return Ms
```

But this gives me

```
line 14 for M in matchings(H):
SyntaxError: invalid syntax
```

I don't understand the error (the loop seems fine to me). What's wrong?