There may be a bug occured when I use 'global' keyword.

If loaded the ipython-autoimport module, It will be found that the x variable can not be changed by function which global keyword is inside.
```
x = "AAAAA"
def myfunc():
  global x
  x = "BBBBB"

myfunc()

print(x)
```

the correct output is "BBBBB", but "AAAAA" output when use ipython autoimport.
