I don't know too much about c#, so maybe someone can expand upon whether that comes with it's own similar problems, but python has a few features and idiosyncrasies that I think will require you to later relearn things, that are common to most major languages, whereas I hear c# is very c-like.
things like using horizontal whitespace to block a subprogram. not have to declare any variables. and inheritance and classes in general are very awkward in python, and to me seem like bad starting points for learning about them. I know classes are something you're going to learn in the first few weeks, but they arrive precisely when programming starts to get really powerful and interesting. so why not already be in a language that will make them both easier to understand, and better prepare you for other languages.
Also, as others said, C# is popping up everywhere. it's getting bigger, where python seems to have it's place, but not one in constant large scale growth