how to declare variable type, C style in python

Python isn't necessarily easier/faster than C, though it's possible that it's simpler ;)

To clarify another statement you made, "you don't have to declare the data type" - it should be restated that you can't declare the data type. When you assign a value to a variable, the type of the value becomes the type of the variable. It's a subtle difference, but different nonetheless.

Edit: Python 3.5 introduced type hints which introduced a way to specify the type of a variable. This answer was written before this feature became available.

There is no way to declare variables in Python, since neither "declaration" nor "variables" in the C sense exist. This will bind the three names to the same object:

x = y = z = 0

Starting with Python 3.6, you can declare types of variables and funtions, like this :

explicit_number: type

or for a function

def function(explicit_number: type) -> type:
    pass

This example from this post: How to Use Static Type Checking in Python 3.6 is more explicit

from typing import Dict

def get_first_name(full_name: str) -> str:
    return full_name.split(" ")[0]

fallback_name: Dict[str, str] = {
    "first_name": "UserFirstName",
    "last_name": "UserLastName"
}

raw_name: str = input("Please enter your name: ")
first_name: str = get_first_name(raw_name)

# If the user didn't type anything in, use the fallback name
if not first_name:
    first_name = get_first_name(fallback_name)

print(f"Hi, {first_name}!")

See the docs for the typing module

Simply said: Typing in python is useful for hinting only.

x: int = 0
y: int = 0 
z: int = 0