I used to do this. But then I realized I would be importing all symbols from std into my code. Including ones that might get defined in the future (similar to python's 'from foo import *'), which might conflict with some of my own symbols.
Hence, I now implicitly import each symbol I need with something like 'using std::map;' (similar to python's 'from foo import bar, bar2').
I've found that the 'using' statement can be used even inside a function to restrict the importation to just a single function.
Interesting; I never thought of that analogy to Python. I've just had it drilled into my head from everything I've ever read about C++ that "using namespace std" is terrible, and I shouldn't use it.
Except the analogy to Python lacks one critical point: C++ headers and Python imports do not work in nearly the same way. Do not EVER use a "using namespace <foo>" in a header file; any code that #include's such a header will pull this in.
In .cpp files it's ok (and almost required if you're using boost, unless you want boost::foo:bar::type everywhere). It still requires a bit of thought, though.