I wonder know what's the difference between a = 1 and a == a?
i got two examples as following:

a = 2
def test():print ("a=", a)a == 3test()

and the result :

a = 2

the other example:

a = 2
def test():print ("a=", a)a = 3test()

and it turned out:

UnboundLocalError: local variable 'a' referenced before assignment

Is there anyone could explain the difference between "=" and "=="?

The difference between the two are:

• == is the operator to check if two objects are equivalent.

• = is the operator to assign value(s) to a variable.

Example:

>>> a = 5 # `=` operator
>>> a
5
>>> a == 5 # `==` operator
True
>>> 

Also the reason why your code returned an error, is because you already have a variable called a outside the function, so there you want to assign it again, it won't work.

Thanks to @SpencerWieczorek for a much better explanation of the part of explanation below the code:

Note: The second example the local a and the global a are entirely different variables. In order to use the global a you defined you would want to add global a at the start of the function. The local variable doesn't have anything to do with the global one and is not the reason for the error.