pandas equivalent of Stata's encode

I'm looking for a way to replicate the encode behaviour in Stata, which will convert a categorical string column into a number column.

x = pd.DataFrame({'cat':['A','A','B'], 'val':[10,20,30]})
x = x.set_index('cat')

Which results in:

     val
cat     
A     10
A     20
B     30

I'd like to convert the cat column from strings to integers, mapping each unique string to an (arbitrary) integer 1-to-1. It would result in:

     val
cat     
1     10
1     20
2     30

Or, just as good:

  cat  val
0   1   10
1   1   20
2   2   30

Any suggestions?

Many thanks as always, Rob