Is it just because of dynamic typing we don't require a concept of interfaces(like in Java and C#) in python?
interface as a keyword and artifact was introduced by Java1 ( and C# took it from there ) to describe what the contract an object must adhere was.
But, interface has always been a key part of Object Oriented Paradigm and basically it represents the methods an object has to respond. Java just enforces this mechanism to provide statically type checking.
So, dynamic ( OO ) programming languages do use interfaces, even thought they don't statically check them. Just like other data types, for instance in Ruby:
@i = 1;
You don't have to declare
i of type
FixNum you just use it. Same goes for interfaces, they just flow. The trade-off is, you can't have a static check on that and failures are only show at runtime.
In the other hand Structural type ( or static duck type as I call it :P ) used by languages as Go or Scala, gives the best of both worlds.
1. See Daniel Earwicker comment about CORBA