I have these keys:

```
keep = ["a","c"]

```

My dict:

```
testdict = {'
'a':'vala',
'b':'valb',
'c':'valc',
'd':'vald'
}

```

Desired output:

```
testdict = {
'a':'vala',
'c':'valc'
}

```

I want to remove all keys that do not match the key in the list.
What is the fastest way to do this?

I tried:

```
for key, value in testdict.iteritems():
      if key not in keep:
         del testdict[key]

```

But the above gives me errors since the size is changing.