The most important part of a crypter is the stub, which is best to be done in assembly.
For the crypter itself it doesn't really matter what language you choose as long as you can do a nice GUI with it (most crypters have a GUI) and have easy access to the WinAPI (given that you want to crypt .exe files) i.e. to make some additional things like icon changing.
That's why .NET languages are often used. They have both: Easy usage of the WinAPI and the most used IDE Visual Studio has a GUI builder.
To get back to your question:
GUI programming in Python:
http://wiki.python.org/moin/GuiProgramming
WinAPI in Python:
http://sourceforge.net/projects/pywin32/
So yes, you can use Python.
If you want to keep the code for yourself, you should consider another language. Python is, even if converted to exe, easily converted back to readable code.
In that case i.e. C++ would be a better choice (without .NET, which has the same problem).
But you also have to learn assembly if you want to make it right.
It is possible without assembly, but you will have a worse result or have to rely on stubs written by others.