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An @ symbol at the beginning of a line is used for class and function decorators: PEP 318: Decorators. Python Decorators - Python Wiki. The most common Python decorators are: @property. @classmethod. @staticmethod. An @ in the middle of a line is probably matrix multiplication: @ as a binary operator.
The % does two things, depending on its arguments. In this case, it acts as the modulo operator, meaning when its arguments are numbers, it divides the first by the second and returns the remainder. 34 % 10 == 4 since 34 divided by 10 is three, with a remainder of four.
When slicing in Python the third parameter is the step. As others mentioned, see Extended Slices for a nice overview. With this knowledge, [::3] just means that you have not specified any start or end indices for your slice. Since you have specified a step, 3, this will take every third entry of something starting at the first index. For example:
Floats and integers are comparable as they are numbers but are usually not equal to each other except when the float is basically the integer but with .0 added to the end. When using ==, if the two items are the same, it will return True. Otherwise, it will return False. You can use = to assign values to variables.
In Python 3.5 though, PEP 484 -- Type Hints attaches a single meaning to this: -> is used to indicate the type that the function returns. It also seems like this will be enforced in future versions as described in What about existing uses of annotations :
180. += adds another value with the variable's value and assigns the new value to the variable. -=, *=, /= does similar for subtraction, multiplication and division. Note that, as the currently most upvoted answer details, x += y is not the same thing as x = x + y, especially if x is a list.
(Additionally, Python specifies x % m to have the sign of m.) // is a division operation that returns an integer by discarding the remainder. This is the standard form of division using the / in most programming languages. However, Python 3 changed the behavior of / to perform floating-point division even if the arguments are integers.
All of the above answers were perfectly clear and complete, but just for the record I'd like to confirm that the meaning of * and ** in python has absolutely no similarity with the meaning of similar-looking operators in C. They are called the argument-unpacking and keyword-argument-unpacking operators.
From the Python 3 docs: The power operator has the same semantics as the built-in pow () function, when called with two arguments: it yields its left argument raised to the power of its right argument. The numeric arguments are first converted to a common type, and the result is of that type. It is equivalent to 2 16 = 65536, or pow(2, 16) Just ...
A Python dict, semantically used for keyword argument passing, is arbitrarily ordered. However, in Python 3.6+, keyword arguments are guaranteed to remember insertion order. "The order of elements in **kwargs now corresponds to the order in which keyword arguments were passed to the function." - What’s New In Python 3.6. In fact, all dicts in ...